diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25e3f669b4..b3df440a3e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -74,6 +74,7 @@ These are only breaking changes for unformatted code.
 - New internal representation for uncurried functions using built-in type `function$<fun_type, arity>` this avoids having to declare all the possible arities ahead of time https://github.com/rescript-lang/rescript-compiler/pull/5870
 - PPX V3: allow uncurried `make` function and treat it like a curried one https://github.com/rescript-lang/rescript-compiler/pull/6081
 - Add support for `|>` in uncurried mode by desugaring it https://github.com/rescript-lang/rescript-compiler/pull/6083
+- Change the compilation of pattern matching for variants so it does not depends on variats being integers https://github.com/rescript-lang/rescript-compiler/pull/6085
 
 # 10.1.4
 
diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index 66e0fb4fba..1199eb5c0b 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -760,6 +760,9 @@ let string_equal ?comment (e0 : t) (e1 : t) : t =
 let is_type_number ?comment (e : t) : t =
   string_equal ?comment (typeof e) (str "number")
 
+let is_tag (e : t) : t =
+  string_equal ~comment:"tag" (typeof e) (str "number")
+
 let is_type_string ?comment (e : t) : t =
   string_equal ?comment (typeof e) (str "string")
 
diff --git a/jscomp/core/js_exp_make.mli b/jscomp/core/js_exp_make.mli
index 351663cceb..00959c53ae 100644
--- a/jscomp/core/js_exp_make.mli
+++ b/jscomp/core/js_exp_make.mli
@@ -199,6 +199,7 @@ val eq_null_undefined_boolean : ?comment:string -> t -> t -> t
 val neq_null_undefined_boolean : ?comment:string -> t -> t -> t
 
 val is_type_number : ?comment:string -> t -> t
+val is_tag : t -> t
 
 val is_type_string : ?comment:string -> t -> t
 
diff --git a/jscomp/core/lam_compile.ml b/jscomp/core/lam_compile.ml
index 2e56858873..a82dc4eb39 100644
--- a/jscomp/core/lam_compile.ml
+++ b/jscomp/core/lam_compile.ml
@@ -616,7 +616,7 @@ and compile_switch (switch_arg : Lam.t) (sw : Lam.lambda_switch)
         else
           (* [e] will be used twice  *)
           let dispatch e =
-            S.if_ (E.is_type_number e)
+            S.if_ (E.is_tag e)
               (compile_cases cxt e sw_consts sw_num_default get_const_name)
               (* default still needed, could simplified*)
               ~else_:
diff --git a/jscomp/core/lam_convert.ml b/jscomp/core/lam_convert.ml
index add8745cbc..87266c46d3 100644
--- a/jscomp/core/lam_convert.ml
+++ b/jscomp/core/lam_convert.ml
@@ -119,16 +119,16 @@ let lam_is_var (x : Lam.t) (y : Ident.t) =
 (** Make sure no int range overflow happens
     also we only check [int]
 *)
-let happens_to_be_diff (sw_consts : (int * Lambda.lambda) list) : int option =
+let happens_to_be_diff (sw_consts : (int * Lambda.lambda) list) sw_names : int option =
   match sw_consts with
   | ( a,
-      Lconst (Const_pointer (a0, Pt_constructor _) | Const_base (Const_int a0))
+      Lconst (Const_base (Const_int a0))
     )
     :: ( b,
          Lconst
-           (Const_pointer (b0, Pt_constructor _) | Const_base (Const_int b0)) )
+           (Const_base (Const_int b0)) )
     :: rest
-    when no_over_flow a && no_over_flow a0 && no_over_flow b && no_over_flow b0
+    when sw_names = None && no_over_flow a && no_over_flow a0 && no_over_flow b && no_over_flow b0
     ->
       let diff = a0 - a in
       if b0 - b = diff then
@@ -136,8 +136,7 @@ let happens_to_be_diff (sw_consts : (int * Lambda.lambda) list) : int option =
           Ext_list.for_all rest (fun (x, lam) ->
               match lam with
               | Lconst
-                  ( Const_pointer (x0, Pt_constructor _)
-                  | Const_base (Const_int x0) )
+                  ( Const_base (Const_int x0) )
                 when no_over_flow x0 && no_over_flow x ->
                   x0 - x = diff
               | _ -> false)
@@ -701,8 +700,9 @@ let convert (exports : Set_ident.t) (lam : Lambda.lambda) :
      sw_numblocks = 0;
      sw_consts;
      sw_numconsts;
+     sw_names;
     } -> (
-        match happens_to_be_diff sw_consts with
+        match happens_to_be_diff sw_consts sw_names with
         | Some 0 -> e
         | Some i ->
             prim ~primitive:Paddint
@@ -712,7 +712,7 @@ let convert (exports : Set_ident.t) (lam : Lambda.lambda) :
                   Lam.const (Const_int { i = Int32.of_int i; comment = None });
                 ]
               Location.none
-        | None ->
+        | _ ->
             Lam.switch e
               {
                 sw_failaction = None;
diff --git a/jscomp/ml/matching.ml b/jscomp/ml/matching.ml
index 4802a3dbf8..6b140691f4 100644
--- a/jscomp/ml/matching.ml
+++ b/jscomp/ml/matching.ml
@@ -2348,19 +2348,25 @@ let combine_constructor sw_names loc arg ex_pat cstr partial ctx def
           match
             (cstr.cstr_consts, cstr.cstr_nonconsts, consts, nonconsts)
           with
-          | (1, 1, [0, act1], [0, act2]) ->
-           (* Typically, match on lists, will avoid isint primitive in that
-              case *)
+          | (1, 1, [0, act1], [0, act2])
+            when cstr.cstr_name = "::" || cstr.cstr_name = "[]" || Datarepr.constructor_has_optional_shape cstr
+           ->
+              (* Typically, match on lists, will avoid isint primitive in that
+                case *)
               let arg = 
                 if !Config.bs_only && Datarepr.constructor_has_optional_shape cstr then
                   Lprim(is_not_none_bs_primitve , [arg], loc)
                 else arg
               in 
                 Lifthenelse(arg, act2, act1)
-          | (2,0, [(i1,act1); (_,act2)],[]) ->
-            if i1 = 0 then Lifthenelse(arg, act2, act1)
-            else Lifthenelse (arg,act1,act2)                
-          | (n,0,_,[])  -> (* The type defines constant constructors only *)
+          | (2,0, [(i1,act1); (_,act2)],[]) when
+            (match act1, act2 with
+            | Lconst (Const_pointer (_, Pt_constructor _ )), _ -> false
+            | _, Lconst (Const_pointer (_, Pt_constructor _ )) -> false
+            | _ -> true) ->
+              if i1 = 0 then Lifthenelse(arg, act2, act1)
+              else Lifthenelse (arg, act1, act2)                
+          | (n,0,_,[]) when false (* relies on tag being an int *) -> (* The type defines constant constructors only *)
               call_switcher loc fail_opt arg 0 (n-1) consts sw_names
           | (n, _, _, _) ->
               let act0  =
@@ -2373,7 +2379,7 @@ let combine_constructor sw_names loc arg ex_pat cstr partial ctx def
                     else None
                 | None,_ -> same_actions nonconsts in
               match act0 with
-              | Some act ->
+              | Some act when false (* relies on tag being an int *) ->
                   Lifthenelse
                     (Lprim (Pisint, [arg], loc),
                      call_switcher loc
@@ -2381,7 +2387,7 @@ let combine_constructor sw_names loc arg ex_pat cstr partial ctx def
                        0 (n-1) consts sw_names,
                      act)
 (* Emit a switch, as bytecode implements this sophisticated instruction *)
-              | None ->
+              | _ ->
                   let sw =
                     {sw_numconsts = cstr.cstr_consts; sw_consts = consts;
                      sw_numblocks = cstr.cstr_nonconsts; sw_blocks = nonconsts;
diff --git a/jscomp/test/adt_optimize_test.js b/jscomp/test/adt_optimize_test.js
index 20f076855e..2ee94ba712 100644
--- a/jscomp/test/adt_optimize_test.js
+++ b/jscomp/test/adt_optimize_test.js
@@ -2,23 +2,58 @@
 
 
 function f(x) {
-  return x + 1 | 0;
+  switch (x) {
+    case /* A */0 :
+        return 1;
+    case /* B */1 :
+        return 2;
+    case /* C */2 :
+        return 3;
+    
+  }
 }
 
 function f_0(x) {
-  return x - 1 | 0;
+  switch (x) {
+    case /* A */0 :
+        return -1;
+    case /* B */1 :
+        return 0;
+    case /* C */2 :
+        return 1;
+    
+  }
 }
 
 function f2(param) {
   if (param >= 3) {
     return /* T003 */3;
-  } else {
-    return param;
+  }
+  switch (param) {
+    case 0 :
+        return /* T000 */0;
+    case 1 :
+        return /* T001 */1;
+    case 2 :
+        return /* T002 */2;
+    
   }
 }
 
 function f3(param) {
-  return param;
+  switch (param) {
+    case /* X0 */0 :
+        return /* Y0 */0;
+    case /* X1 */1 :
+        return /* Y1 */1;
+    case /* X2 */2 :
+        return /* Y2 */2;
+    case /* X3 */3 :
+        return /* Y3 */3;
+    case /* X4 */4 :
+        return /* Y4 */4;
+    
+  }
 }
 
 function f4(param) {
@@ -26,7 +61,7 @@ function f4(param) {
 }
 
 function f5(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* A */0 :
           return 1;
@@ -49,19 +84,21 @@ function f5(param) {
 }
 
 function f6(param) {
-  if (typeof param === "number") {
-    if (param >= 2) {
-      return 2;
-    } else {
-      return 0;
-    }
-  } else {
+  if (/* tag */typeof param !== "number") {
     return 1;
   }
+  switch (param) {
+    case /* A */0 :
+    case /* B */1 :
+        return 0;
+    case /* F */2 :
+        return 2;
+    
+  }
 }
 
 function f7(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* A */0 :
           return 1;
@@ -85,7 +122,7 @@ function f7(param) {
 }
 
 function f8(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* T60 */0 :
       case /* T61 */1 :
@@ -105,7 +142,7 @@ function f8(param) {
 }
 
 function f9(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     if (param === /* T63 */3) {
       return 3;
     } else {
@@ -124,7 +161,7 @@ function f9(param) {
 }
 
 function f10(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* T60 */0 :
           return 0;
@@ -150,7 +187,7 @@ function f10(param) {
 }
 
 function f11(x) {
-  if (typeof x === "number") {
+  if (/* tag */typeof x === "number") {
     return 2;
   }
   if (x.TAG === /* D */0) {
diff --git a/jscomp/test/bal_set_mini.js b/jscomp/test/bal_set_mini.js
index 3b79e9fc9e..b64f0025b7 100644
--- a/jscomp/test/bal_set_mini.js
+++ b/jscomp/test/bal_set_mini.js
@@ -2,10 +2,10 @@
 
 
 function height(param) {
-  if (param) {
-    return param._3;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._3;
   }
 }
 
@@ -24,7 +24,7 @@ function bal(l, v, r) {
   var hl = height(l);
   var hr = height(r);
   if (hl > (hr + 2 | 0)) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return /* Empty */0;
     }
     var lr = l._2;
@@ -32,10 +32,10 @@ function bal(l, v, r) {
     var ll = l._0;
     if (height(ll) >= height(lr)) {
       return create(ll, lv, create(lr, v, r));
-    } else if (lr) {
-      return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
-    } else {
+    } else if (/* tag */typeof lr === "number") {
       return /* Empty */0;
+    } else {
+      return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
     }
   }
   if (hr <= (hl + 2 | 0)) {
@@ -46,7 +46,7 @@ function bal(l, v, r) {
             _3: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (!r) {
+  if (/* tag */typeof r === "number") {
     return /* Empty */0;
   }
   var rr = r._2;
@@ -54,10 +54,10 @@ function bal(l, v, r) {
   var rl = r._0;
   if (height(rr) >= height(rl)) {
     return create(create(l, v, rl), rv, rr);
-  } else if (rl) {
-    return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
-  } else {
+  } else if (/* tag */typeof rl === "number") {
     return /* Empty */0;
+  } else {
+    return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
   }
 }
 
@@ -72,7 +72,7 @@ function compare_int(x, y) {
 }
 
 function add(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -97,11 +97,11 @@ function min_elt(_def, _param) {
   while(true) {
     var param = _param;
     var def = _def;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return def;
     }
     var l = param._0;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return param._1;
     }
     _param = l;
@@ -111,18 +111,18 @@ function min_elt(_def, _param) {
 }
 
 function remove_min_elt(l, v, r) {
-  if (l) {
-    return bal(remove_min_elt(l._0, l._1, l._2), v, r);
-  } else {
+  if (/* tag */typeof l === "number") {
     return r;
+  } else {
+    return bal(remove_min_elt(l._0, l._1, l._2), v, r);
   }
 }
 
 function internal_merge(l, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return r;
   }
-  if (!r) {
+  if (/* tag */typeof r === "number") {
     return l;
   }
   var rv = r._1;
@@ -130,7 +130,7 @@ function internal_merge(l, r) {
 }
 
 function remove(x, tree) {
-  if (!tree) {
+  if (/* tag */typeof tree === "number") {
     return /* Empty */0;
   }
   var r = tree._2;
@@ -149,7 +149,7 @@ function remove(x, tree) {
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = compare_int(x, param._1);
@@ -180,7 +180,7 @@ for(var i$2 = 0; i$2 <= 100000; ++i$2){
 
 var match = v;
 
-if (match) {
+if (/* tag */typeof match !== "number") {
   console.log("impossible");
 }
 
diff --git a/jscomp/test/bdd.js b/jscomp/test/bdd.js
index c8f6a5d75c..3c5a714d60 100644
--- a/jscomp/test/bdd.js
+++ b/jscomp/test/bdd.js
@@ -5,8 +5,12 @@ var Caml_array = require("../../lib/js/caml_array.js");
 function $$eval(_bdd, vars) {
   while(true) {
     var bdd = _bdd;
-    if (typeof bdd === "number") {
-      return bdd === 0;
+    if (/* tag */typeof bdd === "number") {
+      if (bdd === /* One */0) {
+        return true;
+      } else {
+        return false;
+      }
     }
     if (Caml_array.get(vars, bdd._1)) {
       _bdd = bdd._3;
@@ -18,11 +22,11 @@ function $$eval(_bdd, vars) {
 }
 
 function getId(bdd) {
-  if (typeof bdd === "number") {
-    if (bdd !== 0) {
-      return 0;
-    } else {
+  if (/* tag */typeof bdd === "number") {
+    if (bdd === /* One */0) {
       return 1;
+    } else {
+      return 0;
     }
   } else {
     return bdd._2;
@@ -60,7 +64,18 @@ function resize(newSize) {
         return ;
       }
       var n = bucket.hd;
-      if (typeof n === "number") {
+      if (/* tag */typeof n === "number") {
+        if (n === /* One */0) {
+          throw {
+                RE_EXN_ID: "Assert_failure",
+                _1: [
+                  "bdd.ml",
+                  54,
+                  27
+                ],
+                Error: new Error()
+              };
+        }
         throw {
               RE_EXN_ID: "Assert_failure",
               _1: [
@@ -70,14 +85,15 @@ function resize(newSize) {
               ],
               Error: new Error()
             };
+      } else {
+        var ind = hashVal(getId(n._0), getId(n._3), n._1) & newSz_1;
+        Caml_array.set(newArr, ind, {
+              hd: n,
+              tl: Caml_array.get(newArr, ind)
+            });
+        _bucket = bucket.tl;
+        continue ;
       }
-      var ind = hashVal(getId(n._0), getId(n._3), n._1) & newSz_1;
-      Caml_array.set(newArr, ind, {
-            hd: n,
-            tl: Caml_array.get(newArr, ind)
-          });
-      _bucket = bucket.tl;
-      continue ;
     };
   };
   for(var n = 0 ,n_finish = sz_1.contents; n <= n_finish; ++n){
@@ -124,7 +140,18 @@ function mkNode(low, v, high) {
     var b = _b;
     if (b) {
       var n = b.hd;
-      if (typeof n === "number") {
+      if (/* tag */typeof n === "number") {
+        if (n === /* One */0) {
+          throw {
+                RE_EXN_ID: "Assert_failure",
+                _1: [
+                  "bdd.ml",
+                  99,
+                  31
+                ],
+                Error: new Error()
+              };
+        }
         throw {
               RE_EXN_ID: "Assert_failure",
               _1: [
@@ -134,22 +161,24 @@ function mkNode(low, v, high) {
               ],
               Error: new Error()
             };
+      } else {
+        if (v === n._1 && idl === getId(n._0) && idh === getId(n._3)) {
+          return n;
+        }
+        _b = b.tl;
+        continue ;
       }
-      if (v === n._1 && idl === getId(n._0) && idh === getId(n._3)) {
-        return n;
-      }
-      _b = b.tl;
-      continue ;
+    } else {
+      var n_2 = (nodeC.contents = nodeC.contents + 1 | 0, nodeC.contents);
+      var n$1 = /* Node */{
+        _0: low,
+        _1: v,
+        _2: n_2,
+        _3: high
+      };
+      insert(getId(low), getId(high), v, ind, bucket, n$1);
+      return n$1;
     }
-    var n_2 = (nodeC.contents = nodeC.contents + 1 | 0, nodeC.contents);
-    var n$1 = /* Node */{
-      _0: low,
-      _1: v,
-      _2: n_2,
-      _3: high
-    };
-    insert(getId(low), getId(high), v, ind, bucket, n$1);
-    return n$1;
   };
 }
 
@@ -188,11 +217,11 @@ function hash(x, y) {
 }
 
 function not(n) {
-  if (typeof n === "number") {
-    if (n !== 0) {
-      return /* One */0;
-    } else {
+  if (/* tag */typeof n === "number") {
+    if (n === /* One */0) {
       return /* Zero */1;
+    } else {
+      return /* One */0;
     }
   }
   var id = n._2;
@@ -207,22 +236,22 @@ function not(n) {
 }
 
 function and2(n1, n2) {
-  if (typeof n1 === "number") {
-    if (n1 !== 0) {
-      return /* Zero */1;
-    } else {
+  if (/* tag */typeof n1 === "number") {
+    if (n1 === /* One */0) {
       return n2;
+    } else {
+      return /* Zero */1;
     }
   }
   var r1 = n1._3;
   var i1 = n1._2;
   var v1 = n1._1;
   var l1 = n1._0;
-  if (typeof n2 === "number") {
-    if (n2 !== 0) {
-      return /* Zero */1;
-    } else {
+  if (/* tag */typeof n2 === "number") {
+    if (n2 === /* One */0) {
       return n1;
+    } else {
+      return /* Zero */1;
     }
   }
   var r2 = n2._3;
@@ -254,22 +283,22 @@ function and2(n1, n2) {
 }
 
 function xor(n1, n2) {
-  if (typeof n1 === "number") {
-    if (n1 !== 0) {
-      return n2;
-    } else {
+  if (/* tag */typeof n1 === "number") {
+    if (n1 === /* One */0) {
       return not(n2);
+    } else {
+      return n2;
     }
   }
   var r1 = n1._3;
   var i1 = n1._2;
   var v1 = n1._1;
   var l1 = n1._0;
-  if (typeof n2 === "number") {
-    if (n2 !== 0) {
-      return n1;
-    } else {
+  if (/* tag */typeof n2 === "number") {
+    if (n2 === /* One */0) {
       return not(n1);
+    } else {
+      return n1;
     }
   }
   var r2 = n2._3;
diff --git a/jscomp/test/big_enum.js b/jscomp/test/big_enum.js
index 4da3da2481..1022a33d21 100644
--- a/jscomp/test/big_enum.js
+++ b/jscomp/test/big_enum.js
@@ -2,7 +2,609 @@
 
 
 function to_enum(param) {
-  return param;
+  switch (param) {
+    case /* A0 */0 :
+        return 0;
+    case /* A1 */1 :
+        return 1;
+    case /* A2 */2 :
+        return 2;
+    case /* A3 */3 :
+        return 3;
+    case /* A4 */4 :
+        return 4;
+    case /* A5 */5 :
+        return 5;
+    case /* A6 */6 :
+        return 6;
+    case /* A7 */7 :
+        return 7;
+    case /* A8 */8 :
+        return 8;
+    case /* A9 */9 :
+        return 9;
+    case /* A10 */10 :
+        return 10;
+    case /* A11 */11 :
+        return 11;
+    case /* A12 */12 :
+        return 12;
+    case /* A13 */13 :
+        return 13;
+    case /* A14 */14 :
+        return 14;
+    case /* A15 */15 :
+        return 15;
+    case /* A16 */16 :
+        return 16;
+    case /* A17 */17 :
+        return 17;
+    case /* A18 */18 :
+        return 18;
+    case /* A19 */19 :
+        return 19;
+    case /* A20 */20 :
+        return 20;
+    case /* A21 */21 :
+        return 21;
+    case /* A22 */22 :
+        return 22;
+    case /* A23 */23 :
+        return 23;
+    case /* A24 */24 :
+        return 24;
+    case /* A25 */25 :
+        return 25;
+    case /* A26 */26 :
+        return 26;
+    case /* A27 */27 :
+        return 27;
+    case /* A28 */28 :
+        return 28;
+    case /* A29 */29 :
+        return 29;
+    case /* A30 */30 :
+        return 30;
+    case /* A31 */31 :
+        return 31;
+    case /* A32 */32 :
+        return 32;
+    case /* A33 */33 :
+        return 33;
+    case /* A34 */34 :
+        return 34;
+    case /* A35 */35 :
+        return 35;
+    case /* A36 */36 :
+        return 36;
+    case /* A37 */37 :
+        return 37;
+    case /* A38 */38 :
+        return 38;
+    case /* A39 */39 :
+        return 39;
+    case /* A40 */40 :
+        return 40;
+    case /* A41 */41 :
+        return 41;
+    case /* A42 */42 :
+        return 42;
+    case /* A43 */43 :
+        return 43;
+    case /* A44 */44 :
+        return 44;
+    case /* A45 */45 :
+        return 45;
+    case /* A46 */46 :
+        return 46;
+    case /* A47 */47 :
+        return 47;
+    case /* A48 */48 :
+        return 48;
+    case /* A49 */49 :
+        return 49;
+    case /* A50 */50 :
+        return 50;
+    case /* A51 */51 :
+        return 51;
+    case /* A52 */52 :
+        return 52;
+    case /* A53 */53 :
+        return 53;
+    case /* A54 */54 :
+        return 54;
+    case /* A55 */55 :
+        return 55;
+    case /* A56 */56 :
+        return 56;
+    case /* A57 */57 :
+        return 57;
+    case /* A58 */58 :
+        return 58;
+    case /* A59 */59 :
+        return 59;
+    case /* A60 */60 :
+        return 60;
+    case /* A61 */61 :
+        return 61;
+    case /* A62 */62 :
+        return 62;
+    case /* A63 */63 :
+        return 63;
+    case /* A64 */64 :
+        return 64;
+    case /* A65 */65 :
+        return 65;
+    case /* A66 */66 :
+        return 66;
+    case /* A67 */67 :
+        return 67;
+    case /* A68 */68 :
+        return 68;
+    case /* A69 */69 :
+        return 69;
+    case /* A70 */70 :
+        return 70;
+    case /* A71 */71 :
+        return 71;
+    case /* A72 */72 :
+        return 72;
+    case /* A73 */73 :
+        return 73;
+    case /* A74 */74 :
+        return 74;
+    case /* A75 */75 :
+        return 75;
+    case /* A76 */76 :
+        return 76;
+    case /* A77 */77 :
+        return 77;
+    case /* A78 */78 :
+        return 78;
+    case /* A79 */79 :
+        return 79;
+    case /* A80 */80 :
+        return 80;
+    case /* A81 */81 :
+        return 81;
+    case /* A82 */82 :
+        return 82;
+    case /* A83 */83 :
+        return 83;
+    case /* A84 */84 :
+        return 84;
+    case /* A85 */85 :
+        return 85;
+    case /* A86 */86 :
+        return 86;
+    case /* A87 */87 :
+        return 87;
+    case /* A88 */88 :
+        return 88;
+    case /* A89 */89 :
+        return 89;
+    case /* A90 */90 :
+        return 90;
+    case /* A91 */91 :
+        return 91;
+    case /* A92 */92 :
+        return 92;
+    case /* A93 */93 :
+        return 93;
+    case /* A94 */94 :
+        return 94;
+    case /* A95 */95 :
+        return 95;
+    case /* A96 */96 :
+        return 96;
+    case /* A97 */97 :
+        return 97;
+    case /* A98 */98 :
+        return 98;
+    case /* A99 */99 :
+        return 99;
+    case /* A100 */100 :
+        return 100;
+    case /* A101 */101 :
+        return 101;
+    case /* A102 */102 :
+        return 102;
+    case /* A103 */103 :
+        return 103;
+    case /* A104 */104 :
+        return 104;
+    case /* A105 */105 :
+        return 105;
+    case /* A106 */106 :
+        return 106;
+    case /* A107 */107 :
+        return 107;
+    case /* A108 */108 :
+        return 108;
+    case /* A109 */109 :
+        return 109;
+    case /* A110 */110 :
+        return 110;
+    case /* A111 */111 :
+        return 111;
+    case /* A112 */112 :
+        return 112;
+    case /* A113 */113 :
+        return 113;
+    case /* A114 */114 :
+        return 114;
+    case /* A115 */115 :
+        return 115;
+    case /* A116 */116 :
+        return 116;
+    case /* A117 */117 :
+        return 117;
+    case /* A118 */118 :
+        return 118;
+    case /* A119 */119 :
+        return 119;
+    case /* A120 */120 :
+        return 120;
+    case /* A121 */121 :
+        return 121;
+    case /* A122 */122 :
+        return 122;
+    case /* A123 */123 :
+        return 123;
+    case /* A124 */124 :
+        return 124;
+    case /* A125 */125 :
+        return 125;
+    case /* A126 */126 :
+        return 126;
+    case /* A127 */127 :
+        return 127;
+    case /* A128 */128 :
+        return 128;
+    case /* A129 */129 :
+        return 129;
+    case /* A130 */130 :
+        return 130;
+    case /* A131 */131 :
+        return 131;
+    case /* A132 */132 :
+        return 132;
+    case /* A133 */133 :
+        return 133;
+    case /* A134 */134 :
+        return 134;
+    case /* A135 */135 :
+        return 135;
+    case /* A136 */136 :
+        return 136;
+    case /* A137 */137 :
+        return 137;
+    case /* A138 */138 :
+        return 138;
+    case /* A139 */139 :
+        return 139;
+    case /* A140 */140 :
+        return 140;
+    case /* A141 */141 :
+        return 141;
+    case /* A142 */142 :
+        return 142;
+    case /* A143 */143 :
+        return 143;
+    case /* A144 */144 :
+        return 144;
+    case /* A145 */145 :
+        return 145;
+    case /* A146 */146 :
+        return 146;
+    case /* A147 */147 :
+        return 147;
+    case /* A148 */148 :
+        return 148;
+    case /* A149 */149 :
+        return 149;
+    case /* A150 */150 :
+        return 150;
+    case /* A151 */151 :
+        return 151;
+    case /* A152 */152 :
+        return 152;
+    case /* A153 */153 :
+        return 153;
+    case /* A154 */154 :
+        return 154;
+    case /* A155 */155 :
+        return 155;
+    case /* A156 */156 :
+        return 156;
+    case /* A157 */157 :
+        return 157;
+    case /* A158 */158 :
+        return 158;
+    case /* A159 */159 :
+        return 159;
+    case /* A160 */160 :
+        return 160;
+    case /* A161 */161 :
+        return 161;
+    case /* A162 */162 :
+        return 162;
+    case /* A163 */163 :
+        return 163;
+    case /* A164 */164 :
+        return 164;
+    case /* A165 */165 :
+        return 165;
+    case /* A166 */166 :
+        return 166;
+    case /* A167 */167 :
+        return 167;
+    case /* A168 */168 :
+        return 168;
+    case /* A169 */169 :
+        return 169;
+    case /* A170 */170 :
+        return 170;
+    case /* A171 */171 :
+        return 171;
+    case /* A172 */172 :
+        return 172;
+    case /* A173 */173 :
+        return 173;
+    case /* A174 */174 :
+        return 174;
+    case /* A175 */175 :
+        return 175;
+    case /* A176 */176 :
+        return 176;
+    case /* A177 */177 :
+        return 177;
+    case /* A178 */178 :
+        return 178;
+    case /* A179 */179 :
+        return 179;
+    case /* A180 */180 :
+        return 180;
+    case /* A181 */181 :
+        return 181;
+    case /* A182 */182 :
+        return 182;
+    case /* A183 */183 :
+        return 183;
+    case /* A184 */184 :
+        return 184;
+    case /* A185 */185 :
+        return 185;
+    case /* A186 */186 :
+        return 186;
+    case /* A187 */187 :
+        return 187;
+    case /* A188 */188 :
+        return 188;
+    case /* A189 */189 :
+        return 189;
+    case /* A190 */190 :
+        return 190;
+    case /* A191 */191 :
+        return 191;
+    case /* A192 */192 :
+        return 192;
+    case /* A193 */193 :
+        return 193;
+    case /* A194 */194 :
+        return 194;
+    case /* A195 */195 :
+        return 195;
+    case /* A196 */196 :
+        return 196;
+    case /* A197 */197 :
+        return 197;
+    case /* A198 */198 :
+        return 198;
+    case /* A199 */199 :
+        return 199;
+    case /* A200 */200 :
+        return 200;
+    case /* A201 */201 :
+        return 201;
+    case /* A202 */202 :
+        return 202;
+    case /* A203 */203 :
+        return 203;
+    case /* A204 */204 :
+        return 204;
+    case /* A205 */205 :
+        return 205;
+    case /* A206 */206 :
+        return 206;
+    case /* A207 */207 :
+        return 207;
+    case /* A208 */208 :
+        return 208;
+    case /* A209 */209 :
+        return 209;
+    case /* A210 */210 :
+        return 210;
+    case /* A211 */211 :
+        return 211;
+    case /* A212 */212 :
+        return 212;
+    case /* A213 */213 :
+        return 213;
+    case /* A214 */214 :
+        return 214;
+    case /* A215 */215 :
+        return 215;
+    case /* A216 */216 :
+        return 216;
+    case /* A217 */217 :
+        return 217;
+    case /* A218 */218 :
+        return 218;
+    case /* A219 */219 :
+        return 219;
+    case /* A220 */220 :
+        return 220;
+    case /* A221 */221 :
+        return 221;
+    case /* A222 */222 :
+        return 222;
+    case /* A223 */223 :
+        return 223;
+    case /* A224 */224 :
+        return 224;
+    case /* A225 */225 :
+        return 225;
+    case /* A226 */226 :
+        return 226;
+    case /* A227 */227 :
+        return 227;
+    case /* A228 */228 :
+        return 228;
+    case /* A229 */229 :
+        return 229;
+    case /* A230 */230 :
+        return 230;
+    case /* A231 */231 :
+        return 231;
+    case /* A232 */232 :
+        return 232;
+    case /* A233 */233 :
+        return 233;
+    case /* A234 */234 :
+        return 234;
+    case /* A235 */235 :
+        return 235;
+    case /* A236 */236 :
+        return 236;
+    case /* A237 */237 :
+        return 237;
+    case /* A238 */238 :
+        return 238;
+    case /* A239 */239 :
+        return 239;
+    case /* A240 */240 :
+        return 240;
+    case /* A241 */241 :
+        return 241;
+    case /* A242 */242 :
+        return 242;
+    case /* A243 */243 :
+        return 243;
+    case /* A244 */244 :
+        return 244;
+    case /* A245 */245 :
+        return 245;
+    case /* A246 */246 :
+        return 246;
+    case /* A247 */247 :
+        return 247;
+    case /* A248 */248 :
+        return 248;
+    case /* A249 */249 :
+        return 249;
+    case /* A250 */250 :
+        return 250;
+    case /* A251 */251 :
+        return 251;
+    case /* A252 */252 :
+        return 252;
+    case /* A253 */253 :
+        return 253;
+    case /* A254 */254 :
+        return 254;
+    case /* A255 */255 :
+        return 255;
+    case /* A256 */256 :
+        return 256;
+    case /* A257 */257 :
+        return 257;
+    case /* A258 */258 :
+        return 258;
+    case /* A259 */259 :
+        return 259;
+    case /* A260 */260 :
+        return 260;
+    case /* A261 */261 :
+        return 261;
+    case /* A262 */262 :
+        return 262;
+    case /* A263 */263 :
+        return 263;
+    case /* A264 */264 :
+        return 264;
+    case /* A265 */265 :
+        return 265;
+    case /* A266 */266 :
+        return 266;
+    case /* A267 */267 :
+        return 267;
+    case /* A268 */268 :
+        return 268;
+    case /* A269 */269 :
+        return 269;
+    case /* A270 */270 :
+        return 270;
+    case /* A271 */271 :
+        return 271;
+    case /* A272 */272 :
+        return 272;
+    case /* A273 */273 :
+        return 273;
+    case /* A274 */274 :
+        return 274;
+    case /* A275 */275 :
+        return 275;
+    case /* A276 */276 :
+        return 276;
+    case /* A277 */277 :
+        return 277;
+    case /* A278 */278 :
+        return 278;
+    case /* A279 */279 :
+        return 279;
+    case /* A280 */280 :
+        return 280;
+    case /* A281 */281 :
+        return 281;
+    case /* A282 */282 :
+        return 282;
+    case /* A283 */283 :
+        return 283;
+    case /* A284 */284 :
+        return 284;
+    case /* A285 */285 :
+        return 285;
+    case /* A286 */286 :
+        return 286;
+    case /* A287 */287 :
+        return 287;
+    case /* A288 */288 :
+        return 288;
+    case /* A289 */289 :
+        return 289;
+    case /* A290 */290 :
+        return 290;
+    case /* A291 */291 :
+        return 291;
+    case /* A292 */292 :
+        return 292;
+    case /* A293 */293 :
+        return 293;
+    case /* A294 */294 :
+        return 294;
+    case /* A295 */295 :
+        return 295;
+    case /* A296 */296 :
+        return 296;
+    case /* A297 */297 :
+        return 297;
+    case /* A298 */298 :
+        return 298;
+    case /* A299 */299 :
+        return 299;
+    
+  }
 }
 
 function to_string(param) {
diff --git a/jscomp/test/build.ninja b/jscomp/test/build.ninja
index 5aa4ac9571..4f6ce47b11 100644
--- a/jscomp/test/build.ninja
+++ b/jscomp/test/build.ninja
@@ -723,6 +723,7 @@ o test/unsafe_this.cmi : cc test/unsafe_this.mli | $bsc $stdlib runtime
 o test/update_record_test.cmi test/update_record_test.cmj : cc test/update_record_test.ml | test/mt.cmj $bsc $stdlib runtime
 o test/utf8_decode_test.cmi test/utf8_decode_test.cmj : cc test/utf8_decode_test.ml | test/mt.cmj $bsc $stdlib runtime
 o test/variant.cmi test/variant.cmj : cc test/variant.ml | $bsc $stdlib runtime
+o test/variantsMatching.cmi test/variantsMatching.cmj : cc test/variantsMatching.res | $bsc $stdlib runtime
 o test/watch_test.cmi test/watch_test.cmj : cc test/watch_test.ml | $bsc $stdlib runtime
 o test/webpack_config.cmi test/webpack_config.cmj : cc test/webpack_config.ml | $bsc $stdlib runtime
-o test : phony test/406_primitive_test.cmi test/406_primitive_test.cmj test/EmptyRecord.cmi test/EmptyRecord.cmj test/SafePromises.cmi test/SafePromises.cmj test/UncurriedAlways.cmi test/UncurriedAlways.cmj test/UncurriedExternals.cmi test/UncurriedExternals.cmj test/UncurriedPervasives.cmi test/UncurriedPervasives.cmj test/a.cmi test/a.cmj test/a_filename_test.cmi test/a_filename_test.cmj test/a_list_test.cmi test/a_list_test.cmj test/a_recursive_type.cmi test/a_recursive_type.cmj test/a_scope_bug.cmi test/a_scope_bug.cmj test/a_string_test.cmi test/a_string_test.cmj test/abstract_type.cmi test/abstract_type.cmj test/adt_optimize_test.cmi test/adt_optimize_test.cmj test/alias_default_value_test.cmi test/alias_default_value_test.cmj test/alias_test.cmi test/alias_test.cmj test/and_or_tailcall_test.cmi test/and_or_tailcall_test.cmj test/app_root_finder.cmi test/app_root_finder.cmj test/argv_test.cmi test/argv_test.cmj test/ari_regress_test.cmi test/ari_regress_test.cmj test/arith_lexer.cmi test/arith_lexer.cmj test/arith_parser.cmi test/arith_parser.cmj test/arith_syntax.cmi test/arith_syntax.cmj test/arity.cmi test/arity.cmj test/arity_deopt.cmi test/arity_deopt.cmj test/arity_infer.cmi test/arity_infer.cmj test/array_data_util.cmi test/array_data_util.cmj test/array_safe_get.cmi test/array_safe_get.cmj test/array_subtle_test.cmi test/array_subtle_test.cmj test/array_test.cmi test/array_test.cmj test/ast_abstract_test.cmi test/ast_abstract_test.cmj test/ast_js_mapper_poly_test.cmi test/ast_js_mapper_poly_test.cmj test/ast_js_mapper_test.cmi test/ast_js_mapper_test.cmj test/ast_mapper_defensive_test.cmi test/ast_mapper_defensive_test.cmj test/ast_mapper_unused_warning_test.cmi test/ast_mapper_unused_warning_test.cmj test/async_await.cmi test/async_await.cmj test/async_ideas.cmi test/async_ideas.cmj test/async_inline.cmi test/async_inline.cmj test/attr_test.cmi test/attr_test.cmj test/b.cmi test/b.cmj test/bal_set_mini.cmi test/bal_set_mini.cmj test/bang_primitive.cmi test/bang_primitive.cmj test/basic_module_test.cmi test/basic_module_test.cmj test/bb.cmi test/bb.cmj test/bdd.cmi test/bdd.cmj test/belt_internal_test.cmi test/belt_internal_test.cmj test/belt_result_alias_test.cmi test/belt_result_alias_test.cmj test/bench.cmi test/bench.cmj test/big_enum.cmi test/big_enum.cmj test/big_polyvar_test.cmi test/big_polyvar_test.cmj test/block_alias_test.cmi test/block_alias_test.cmj test/boolean_test.cmi test/boolean_test.cmj test/bs_MapInt_test.cmi test/bs_MapInt_test.cmj test/bs_abstract_test.cmi test/bs_abstract_test.cmj test/bs_array_test.cmi test/bs_array_test.cmj test/bs_auto_uncurry.cmi test/bs_auto_uncurry.cmj test/bs_auto_uncurry_test.cmi test/bs_auto_uncurry_test.cmj test/bs_float_test.cmi test/bs_float_test.cmj test/bs_hashmap_test.cmi test/bs_hashmap_test.cmj test/bs_hashset_int_test.cmi test/bs_hashset_int_test.cmj test/bs_hashtbl_string_test.cmi test/bs_hashtbl_string_test.cmj test/bs_ignore_effect.cmi test/bs_ignore_effect.cmj test/bs_ignore_test.cmi test/bs_ignore_test.cmj test/bs_int_test.cmi test/bs_int_test.cmj test/bs_list_test.cmi test/bs_list_test.cmj test/bs_map_set_dict_test.cmi test/bs_map_set_dict_test.cmj test/bs_map_test.cmi test/bs_map_test.cmj test/bs_min_max_test.cmi test/bs_min_max_test.cmj test/bs_mutable_set_test.cmi test/bs_mutable_set_test.cmj test/bs_node_string_buffer_test.cmi test/bs_node_string_buffer_test.cmj test/bs_poly_map_test.cmi test/bs_poly_map_test.cmj test/bs_poly_mutable_map_test.cmi test/bs_poly_mutable_map_test.cmj test/bs_poly_mutable_set_test.cmi test/bs_poly_mutable_set_test.cmj test/bs_poly_set_test.cmi test/bs_poly_set_test.cmj test/bs_qualified.cmi test/bs_qualified.cmj test/bs_queue_test.cmi test/bs_queue_test.cmj test/bs_rbset_int_bench.cmi test/bs_rbset_int_bench.cmj test/bs_rest_test.cmi test/bs_rest_test.cmj test/bs_set_bench.cmi test/bs_set_bench.cmj test/bs_set_int_test.cmi test/bs_set_int_test.cmj test/bs_sort_test.cmi 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test/rebind_module_test.cmi test/rebind_module_test.cmj test/rec_array_test.cmi test/rec_array_test.cmj test/rec_fun_test.cmi test/rec_fun_test.cmj test/rec_module_opt.cmi test/rec_module_opt.cmj test/rec_module_test.cmi test/rec_module_test.cmj test/rec_value_test.cmi test/rec_value_test.cmj test/record_debug_test.cmi test/record_debug_test.cmj test/record_extension_test.cmi test/record_extension_test.cmj test/record_name_test.cmi test/record_name_test.cmj test/record_regression.cmi test/record_regression.cmj test/record_with_test.cmi test/record_with_test.cmj test/recursive_module.cmi test/recursive_module.cmj test/recursive_module_test.cmi test/recursive_module_test.cmj test/recursive_react_component.cmi test/recursive_react_component.cmj test/recursive_records_test.cmi test/recursive_records_test.cmj test/recursive_unbound_module_test.cmi test/recursive_unbound_module_test.cmj test/regression_print.cmi test/regression_print.cmj test/relative_path.cmi test/relative_path.cmj 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test/then_mangle_test.cmj test/ticker.cmi test/ticker.cmj test/to_string_test.cmi test/to_string_test.cmj test/topsort_test.cmi test/topsort_test.cmj test/tramp_fib.cmi test/tramp_fib.cmj test/tuple_alloc.cmi test/tuple_alloc.cmj test/type_disambiguate.cmi test/type_disambiguate.cmj test/typeof_test.cmi test/typeof_test.cmj test/ui_defs.cmi test/unboxed_attribute.cmi test/unboxed_attribute.cmj test/unboxed_attribute_test.cmi test/unboxed_attribute_test.cmj test/unboxed_crash.cmi test/unboxed_crash.cmj test/unboxed_use_case.cmi test/unboxed_use_case.cmj test/uncurried_cast.cmi test/uncurried_cast.cmj test/uncurried_default.args.cmi test/uncurried_default.args.cmj test/uncurried_pipe.cmi test/uncurried_pipe.cmj test/uncurry_external_test.cmi test/uncurry_external_test.cmj test/uncurry_glob_test.cmi test/uncurry_glob_test.cmj test/uncurry_test.cmi test/uncurry_test.cmj test/undef_regression2_test.cmi test/undef_regression2_test.cmj test/undef_regression_test.cmi 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+o test : phony test/406_primitive_test.cmi test/406_primitive_test.cmj test/EmptyRecord.cmi test/EmptyRecord.cmj test/SafePromises.cmi test/SafePromises.cmj test/UncurriedAlways.cmi test/UncurriedAlways.cmj test/UncurriedExternals.cmi test/UncurriedExternals.cmj test/UncurriedPervasives.cmi test/UncurriedPervasives.cmj test/a.cmi test/a.cmj test/a_filename_test.cmi test/a_filename_test.cmj test/a_list_test.cmi test/a_list_test.cmj test/a_recursive_type.cmi test/a_recursive_type.cmj test/a_scope_bug.cmi test/a_scope_bug.cmj test/a_string_test.cmi test/a_string_test.cmj test/abstract_type.cmi test/abstract_type.cmj test/adt_optimize_test.cmi test/adt_optimize_test.cmj test/alias_default_value_test.cmi test/alias_default_value_test.cmj test/alias_test.cmi test/alias_test.cmj test/and_or_tailcall_test.cmi test/and_or_tailcall_test.cmj test/app_root_finder.cmi test/app_root_finder.cmj test/argv_test.cmi test/argv_test.cmj test/ari_regress_test.cmi test/ari_regress_test.cmj 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test/test_array.cmj test/test_array_append.cmi test/test_array_append.cmj test/test_array_primitive.cmi test/test_array_primitive.cmj test/test_bool_equal.cmi test/test_bool_equal.cmj test/test_bs_this.cmi test/test_bs_this.cmj test/test_bug.cmi test/test_bug.cmj test/test_bytes.cmi test/test_bytes.cmj test/test_case_opt_collision.cmi test/test_case_opt_collision.cmj test/test_case_set.cmi test/test_case_set.cmj test/test_char.cmi test/test_char.cmj test/test_closure.cmi test/test_closure.cmj test/test_common.cmi test/test_common.cmj test/test_const_elim.cmi test/test_const_elim.cmj test/test_const_propogate.cmi test/test_const_propogate.cmj test/test_cpp.cmi test/test_cpp.cmj test/test_cps.cmi test/test_cps.cmj test/test_demo.cmi test/test_demo.cmj test/test_dup_param.cmi test/test_dup_param.cmj test/test_eq.cmi test/test_eq.cmj test/test_exception.cmi test/test_exception.cmj test/test_exception_escape.cmi test/test_exception_escape.cmj test/test_export2.cmi test/test_export2.cmj test/test_external.cmi test/test_external.cmj test/test_external_unit.cmi test/test_external_unit.cmj test/test_ffi.cmi test/test_ffi.cmj test/test_fib.cmi test/test_fib.cmj test/test_filename.cmi test/test_filename.cmj test/test_for_loop.cmi test/test_for_loop.cmj test/test_for_map.cmi test/test_for_map.cmj test/test_for_map2.cmi test/test_for_map2.cmj test/test_format.cmi test/test_format.cmj test/test_formatter.cmi test/test_formatter.cmj test/test_functor_dead_code.cmi test/test_functor_dead_code.cmj test/test_generative_module.cmi test/test_generative_module.cmj test/test_global_print.cmi test/test_global_print.cmj test/test_google_closure.cmi test/test_google_closure.cmj test/test_include.cmi test/test_include.cmj test/test_incomplete.cmi test/test_incomplete.cmj test/test_incr_ref.cmi test/test_incr_ref.cmj test/test_int_map_find.cmi test/test_int_map_find.cmj test/test_internalOO.cmi test/test_internalOO.cmj test/test_is_js.cmi test/test_is_js.cmj test/test_js_ffi.cmi test/test_js_ffi.cmj test/test_let.cmi test/test_let.cmj test/test_list.cmi test/test_list.cmj test/test_literal.cmi test/test_literal.cmj test/test_literals.cmi test/test_literals.cmj test/test_match_exception.cmi test/test_match_exception.cmj test/test_mutliple.cmi test/test_mutliple.cmj test/test_nat64.cmi test/test_nat64.cmj test/test_nested_let.cmi test/test_nested_let.cmj test/test_nested_print.cmi test/test_nested_print.cmj test/test_non_export.cmi test/test_non_export.cmj test/test_nullary.cmi test/test_nullary.cmj test/test_obj.cmi test/test_obj.cmj test/test_obj_simple_ffi.cmi test/test_obj_simple_ffi.cmj test/test_order.cmi test/test_order.cmj test/test_order_tailcall.cmi test/test_order_tailcall.cmj test/test_other_exn.cmi test/test_other_exn.cmj test/test_pack.cmi test/test_pack.cmj test/test_per.cmi test/test_per.cmj test/test_pervasive.cmi test/test_pervasive.cmj test/test_pervasives2.cmi test/test_pervasives2.cmj test/test_pervasives3.cmi test/test_pervasives3.cmj test/test_primitive.cmi test/test_primitive.cmj test/test_ramification.cmi test/test_ramification.cmj test/test_react.cmi test/test_react.cmj test/test_react_case.cmi test/test_react_case.cmj test/test_regex.cmi test/test_regex.cmj test/test_require.cmi test/test_require.cmj test/test_runtime_encoding.cmi test/test_runtime_encoding.cmj test/test_scope.cmi test/test_scope.cmj test/test_seq.cmi test/test_seq.cmj test/test_set.cmi test/test_set.cmj test/test_side_effect_functor.cmi test/test_side_effect_functor.cmj test/test_simple_include.cmi test/test_simple_include.cmj test/test_simple_pattern_match.cmi test/test_simple_pattern_match.cmj test/test_simple_ref.cmi test/test_simple_ref.cmj test/test_simple_tailcall.cmi test/test_simple_tailcall.cmj test/test_small.cmi test/test_small.cmj test/test_sprintf.cmi test/test_sprintf.cmj test/test_stack.cmi test/test_stack.cmj test/test_static_catch_ident.cmi test/test_static_catch_ident.cmj test/test_string.cmi test/test_string.cmj test/test_string_case.cmi test/test_string_case.cmj test/test_string_const.cmi test/test_string_const.cmj test/test_string_map.cmi test/test_string_map.cmj test/test_string_switch.cmi test/test_string_switch.cmj test/test_switch.cmi test/test_switch.cmj test/test_trywith.cmi test/test_trywith.cmj test/test_tuple.cmi test/test_tuple.cmj test/test_tuple_destructring.cmi test/test_tuple_destructring.cmj test/test_type_based_arity.cmi test/test_type_based_arity.cmj test/test_u.cmi test/test_u.cmj test/test_unknown.cmi test/test_unknown.cmj test/test_unsafe_cmp.cmi test/test_unsafe_cmp.cmj test/test_unsafe_obj_ffi.cmi test/test_unsafe_obj_ffi.cmj test/test_unsafe_obj_ffi_ppx.cmi test/test_unsafe_obj_ffi_ppx.cmj test/test_unsupported_primitive.cmi test/test_unsupported_primitive.cmj test/test_while_closure.cmi test/test_while_closure.cmj test/test_while_side_effect.cmi test/test_while_side_effect.cmj test/test_zero_nullable.cmi test/test_zero_nullable.cmj test/then_mangle_test.cmi test/then_mangle_test.cmj test/ticker.cmi test/ticker.cmj test/to_string_test.cmi test/to_string_test.cmj test/topsort_test.cmi test/topsort_test.cmj test/tramp_fib.cmi test/tramp_fib.cmj test/tuple_alloc.cmi test/tuple_alloc.cmj test/type_disambiguate.cmi test/type_disambiguate.cmj test/typeof_test.cmi test/typeof_test.cmj test/ui_defs.cmi test/unboxed_attribute.cmi test/unboxed_attribute.cmj test/unboxed_attribute_test.cmi test/unboxed_attribute_test.cmj test/unboxed_crash.cmi test/unboxed_crash.cmj test/unboxed_use_case.cmi test/unboxed_use_case.cmj test/uncurried_cast.cmi test/uncurried_cast.cmj test/uncurried_default.args.cmi test/uncurried_default.args.cmj test/uncurried_pipe.cmi test/uncurried_pipe.cmj test/uncurry_external_test.cmi test/uncurry_external_test.cmj test/uncurry_glob_test.cmi test/uncurry_glob_test.cmj test/uncurry_test.cmi test/uncurry_test.cmj test/undef_regression2_test.cmi test/undef_regression2_test.cmj test/undef_regression_test.cmi test/undef_regression_test.cmj test/undefine_conditional.cmi test/undefine_conditional.cmj test/unicode_type_error.cmi test/unicode_type_error.cmj test/unit_undefined_test.cmi test/unit_undefined_test.cmj test/unitest_string.cmi test/unitest_string.cmj test/unsafe_full_apply_primitive.cmi test/unsafe_full_apply_primitive.cmj test/unsafe_ppx_test.cmi test/unsafe_ppx_test.cmj test/unsafe_this.cmi test/unsafe_this.cmj test/update_record_test.cmi test/update_record_test.cmj test/utf8_decode_test.cmi test/utf8_decode_test.cmj test/variant.cmi test/variant.cmj test/variantsMatching.cmi test/variantsMatching.cmj test/watch_test.cmi test/watch_test.cmj test/webpack_config.cmi test/webpack_config.cmj
diff --git a/jscomp/test/compare_test.js b/jscomp/test/compare_test.js
index b9cd0a9446..d6168a7567 100644
--- a/jscomp/test/compare_test.js
+++ b/jscomp/test/compare_test.js
@@ -16,11 +16,32 @@ function compare(x, y) {
 function compare2(x, y) {
   switch (x) {
     case /* A */0 :
-        return y === 0;
+        switch (y) {
+          case /* A */0 :
+              return true;
+          case /* B */1 :
+          case /* C */2 :
+              return false;
+          
+        }
     case /* B */1 :
-        return y === 1;
+        switch (y) {
+          case /* B */1 :
+              return true;
+          case /* A */0 :
+          case /* C */2 :
+              return false;
+          
+        }
     case /* C */2 :
-        return y >= 2;
+        switch (y) {
+          case /* A */0 :
+          case /* B */1 :
+              return false;
+          case /* C */2 :
+              return true;
+          
+        }
     
   }
 }
diff --git a/jscomp/test/defunctor_make_test.js b/jscomp/test/defunctor_make_test.js
index ca8e69d1fc..59df578281 100644
--- a/jscomp/test/defunctor_make_test.js
+++ b/jscomp/test/defunctor_make_test.js
@@ -16,10 +16,10 @@ var Comparable = {
 };
 
 function height(param) {
-  if (param) {
-    return param._4;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._4;
   }
 }
 
@@ -36,26 +36,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l._4 : 0;
-  var hr = r ? r._4 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._4;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._4;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._3;
-      var ld = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l._3;
+    var ld = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -71,23 +73,23 @@ function bal(l, x, d, r) {
             _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._3;
-    var rd = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r._3;
+  var rd = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -96,7 +98,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, compare, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
diff --git a/jscomp/test/demo_int_map.js b/jscomp/test/demo_int_map.js
index b06d603d6a..5be0b06730 100644
--- a/jscomp/test/demo_int_map.js
+++ b/jscomp/test/demo_int_map.js
@@ -2,10 +2,10 @@
 
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -22,26 +22,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -57,23 +59,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -82,7 +84,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -128,18 +130,18 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = x - param.v | 0;
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = x - param.v | 0;
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/demo_page.js b/jscomp/test/demo_page.js
index c111ebd498..6cce5b607e 100644
--- a/jscomp/test/demo_page.js
+++ b/jscomp/test/demo_page.js
@@ -21,13 +21,13 @@ function sum(n) {
 }
 
 function map(f, param) {
-  if (param) {
+  if (/* tag */typeof param === "number") {
+    return /* Nil */0;
+  } else {
     return /* Cons */{
             _0: Curry._1(f, param._0),
             _1: map(f, param._1)
           };
-  } else {
-    return /* Nil */0;
   }
 }
 
diff --git a/jscomp/test/flexible_array_test.js b/jscomp/test/flexible_array_test.js
index 06160e3c4f..fcee2d0ab1 100644
--- a/jscomp/test/flexible_array_test.js
+++ b/jscomp/test/flexible_array_test.js
@@ -9,134 +9,135 @@ function sub(_tr, _k) {
   while(true) {
     var k = _k;
     var tr = _tr;
-    if (tr) {
-      if (k === 1) {
-        return tr._0;
-      }
-      if (k % 2 === 0) {
-        _k = k / 2 | 0;
-        _tr = tr._1;
-        continue ;
-      }
+    if (/* tag */typeof tr === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    if (k === 1) {
+      return tr._0;
+    }
+    if (k % 2 === 0) {
       _k = k / 2 | 0;
-      _tr = tr._2;
+      _tr = tr._1;
       continue ;
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _k = k / 2 | 0;
+    _tr = tr._2;
+    continue ;
   };
 }
 
 function update(tr, k, w) {
-  if (tr) {
-    var r = tr._2;
-    var l = tr._1;
+  if (/* tag */typeof tr === "number") {
     if (k === 1) {
       return /* Br */{
               _0: w,
-              _1: l,
-              _2: r
-            };
-    }
-    var v = tr._0;
-    if (k % 2 === 0) {
-      return /* Br */{
-              _0: v,
-              _1: update(l, k / 2 | 0, w),
-              _2: r
-            };
-    } else {
-      return /* Br */{
-              _0: v,
-              _1: l,
-              _2: update(r, k / 2 | 0, w)
+              _1: /* Lf */0,
+              _2: /* Lf */0
             };
     }
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
   }
+  var r = tr._2;
+  var l = tr._1;
   if (k === 1) {
     return /* Br */{
             _0: w,
-            _1: /* Lf */0,
-            _2: /* Lf */0
+            _1: l,
+            _2: r
+          };
+  }
+  var v = tr._0;
+  if (k % 2 === 0) {
+    return /* Br */{
+            _0: v,
+            _1: update(l, k / 2 | 0, w),
+            _2: r
+          };
+  } else {
+    return /* Br */{
+            _0: v,
+            _1: l,
+            _2: update(r, k / 2 | 0, w)
           };
   }
-  throw {
-        RE_EXN_ID: "Not_found",
-        Error: new Error()
-      };
 }
 
 function $$delete(tr, n) {
-  if (tr) {
-    if (n === 1) {
-      return /* Lf */0;
-    }
-    var r = tr._2;
-    var l = tr._1;
-    var v = tr._0;
-    if (n % 2 === 0) {
-      return /* Br */{
-              _0: v,
-              _1: $$delete(l, n / 2 | 0),
-              _2: r
-            };
-    } else {
-      return /* Br */{
-              _0: v,
-              _1: l,
-              _2: $$delete(r, n / 2 | 0)
-            };
-    }
+  if (/* tag */typeof tr === "number") {
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
+  }
+  if (n === 1) {
+    return /* Lf */0;
+  }
+  var r = tr._2;
+  var l = tr._1;
+  var v = tr._0;
+  if (n % 2 === 0) {
+    return /* Br */{
+            _0: v,
+            _1: $$delete(l, n / 2 | 0),
+            _2: r
+          };
+  } else {
+    return /* Br */{
+            _0: v,
+            _1: l,
+            _2: $$delete(r, n / 2 | 0)
+          };
   }
-  throw {
-        RE_EXN_ID: "Not_found",
-        Error: new Error()
-      };
 }
 
 function loext(tr, w) {
-  if (tr) {
+  if (/* tag */typeof tr === "number") {
     return /* Br */{
             _0: w,
-            _1: loext(tr._2, tr._0),
-            _2: tr._1
+            _1: /* Lf */0,
+            _2: /* Lf */0
           };
   } else {
     return /* Br */{
             _0: w,
-            _1: /* Lf */0,
-            _2: /* Lf */0
+            _1: loext(tr._2, tr._0),
+            _2: tr._1
           };
   }
 }
 
 function lorem(tr) {
-  if (tr) {
-    var l = tr._1;
-    if (l) {
-      return /* Br */{
-              _0: l._0,
-              _1: tr._2,
-              _2: lorem(l)
-            };
-    }
-    if (!tr._2) {
-      return /* Lf */0;
-    }
+  if (/* tag */typeof tr === "number") {
     throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "flexible_array_test.ml",
-            66,
-            9
-          ],
+          RE_EXN_ID: "Not_found",
           Error: new Error()
         };
   }
+  var l = tr._1;
+  if (/* tag */typeof l !== "number") {
+    return /* Br */{
+            _0: l._0,
+            _1: tr._2,
+            _2: lorem(l)
+          };
+  }
+  var tmp = tr._2;
+  if (/* tag */typeof tmp === "number") {
+    return /* Lf */0;
+  }
   throw {
-        RE_EXN_ID: "Not_found",
+        RE_EXN_ID: "Assert_failure",
+        _1: [
+          "flexible_array_test.ml",
+          66,
+          9
+        ],
         Error: new Error()
       };
 }
diff --git a/jscomp/test/flow_parser_reg_test.js b/jscomp/test/flow_parser_reg_test.js
index 69602d9c49..2f240c5f70 100644
--- a/jscomp/test/flow_parser_reg_test.js
+++ b/jscomp/test/flow_parser_reg_test.js
@@ -84,7 +84,7 @@ function btwn_exclusive(loc1, loc2) {
 }
 
 function string_of_filename(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     return "(global)";
   } else {
     return param._0;
@@ -92,7 +92,7 @@ function string_of_filename(param) {
 }
 
 function order_of_filename(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     return 1;
   }
   switch (param.TAG | 0) {
@@ -1500,7 +1500,7 @@ Caml_module.update_mod({
     }, Class, Class);
 
 function token_to_string(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* T_IDENTIFIER */0 :
           return "T_IDENTIFIER";
@@ -1824,7 +1824,7 @@ function get_result_and_clear_state(param) {
   var env = match[0];
   var match$1;
   var exit = 0;
-  if (typeof lex_token === "number") {
+  if (/* tag */typeof lex_token === "number") {
     exit = 2;
   } else {
     switch (lex_token.TAG | 0) {
@@ -2304,21 +2304,18 @@ function utf16to8(code) {
 
 function mk_num_singleton(number_type, num, neg) {
   var value;
-  if (number_type !== 0) {
-    switch (number_type) {
-      case /* LEGACY_OCTAL */1 :
-          value = Caml_format.int_of_string("0o" + num);
-          break;
-      case /* OCTAL */2 :
-          value = Caml_format.int_of_string(num);
-          break;
-      case /* NORMAL */3 :
-          value = float_of_string(num);
-          break;
-      
-    }
-  } else {
-    value = Caml_format.int_of_string(num);
+  switch (number_type) {
+    case /* LEGACY_OCTAL */1 :
+        value = Caml_format.int_of_string("0o" + num);
+        break;
+    case /* BINARY */0 :
+    case /* OCTAL */2 :
+        value = Caml_format.int_of_string(num);
+        break;
+    case /* NORMAL */3 :
+        value = float_of_string(num);
+        break;
+    
   }
   var value$1 = neg === "" ? value : - value;
   return {
@@ -5274,16 +5271,18 @@ function token$1(env) {
 }
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -5293,25 +5292,27 @@ function create(l, v, r) {
 }
 
 function bal(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, create(lr, v, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, create(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -5326,22 +5327,22 @@ function bal(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -5350,7 +5351,7 @@ function bal(l, v, r) {
 }
 
 function add(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -5384,7 +5385,7 @@ function add(x, t) {
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.string_compare(x, param.v);
@@ -5519,7 +5520,7 @@ function init_env(token_sinkOpt, parse_optionsOpt, source, content) {
   var token_sink = token_sinkOpt !== undefined ? Caml_option.valFromOption(token_sinkOpt) : undefined;
   var parse_options = parse_optionsOpt !== undefined ? Caml_option.valFromOption(parse_optionsOpt) : undefined;
   var lb = Lexing.from_string(content);
-  if (source !== undefined && typeof source !== "number") {
+  if (source !== undefined && /* tag */typeof source !== "number") {
     var init = lb.lex_curr_p;
     lb.lex_curr_p = {
       pos_fname: source._0,
@@ -5822,20 +5823,17 @@ function is_line_terminator(env) {
 
 function is_implicit_semicolon(env) {
   var match = token$2(undefined, env);
-  if (typeof match === "number") {
-    if (match > 104 || match < 3) {
-      if (match > 105 || match < 2) {
-        return is_line_terminator(env);
-      } else {
+  if (/* tag */typeof match !== "number") {
+    return is_line_terminator(env);
+  }
+  switch (match) {
+    case /* T_SEMICOLON */7 :
+        return false;
+    case /* T_RCURLY */2 :
+    case /* T_EOF */105 :
         return true;
-      }
-    } else if (match !== 7) {
+    default:
       return is_line_terminator(env);
-    } else {
-      return false;
-    }
-  } else {
-    return is_line_terminator(env);
   }
 }
 
@@ -5853,15 +5851,22 @@ function is_identifier(iOpt, env) {
   var match = token$2(i, env);
   if (is_strict_reserved(name) || is_restricted(name) || is_future_reserved(name)) {
     return true;
-  } else if (typeof match === "number") {
-    if (match > 57 || match < 1) {
-      return match < 63;
-    } else {
-      return match === 26;
-    }
-  } else {
+  }
+  if (/* tag */typeof match !== "number") {
     return false;
   }
+  switch (match) {
+    case /* T_IDENTIFIER */0 :
+    case /* T_LET */26 :
+    case /* T_DECLARE */58 :
+    case /* T_TYPE */59 :
+    case /* T_OF */60 :
+    case /* T_ASYNC */61 :
+    case /* T_AWAIT */62 :
+        return true;
+    default:
+      return false;
+  }
 }
 
 function is_function(iOpt, env) {
@@ -5878,15 +5883,16 @@ function is_function(iOpt, env) {
 function is_class(iOpt, env) {
   var i = iOpt !== undefined ? iOpt : 0;
   var match = token$2(i, env);
-  if (typeof match === "number") {
-    if (match !== 12) {
-      return match === 38;
-    } else {
-      return true;
-    }
-  } else {
+  if (/* tag */typeof match !== "number") {
     return false;
   }
+  switch (match) {
+    case /* T_AT */12 :
+    case /* T_CLASS */38 :
+        return true;
+    default:
+      return false;
+  }
 }
 
 function error(env, e) {
@@ -5899,7 +5905,7 @@ function error(env, e) {
 
 function get_unexpected_error(param) {
   var tmp = param[0];
-  if (typeof tmp === "number") {
+  if (/* tag */typeof tmp === "number") {
     switch (tmp) {
       case /* T_IDENTIFIER */0 :
           return /* UnexpectedIdentifier */2;
@@ -6165,16 +6171,18 @@ var Parser_env_Try = {
 };
 
 function height$1(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create$2(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -6184,25 +6192,27 @@ function create$2(l, v, r) {
 }
 
 function bal$1(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$1(ll) >= height$1(lr)) {
-        return create$2(ll, lv, create$2(lr, v, r));
-      }
-      if (lr) {
-        return create$2(create$2(ll, lv, lr.l), lr.v, create$2(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$1(ll) >= height$1(lr)) {
+      return create$2(ll, lv, create$2(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$2(create$2(ll, lv, lr.l), lr.v, create$2(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -6217,22 +6227,22 @@ function bal$1(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$1(rr) >= height$1(rl)) {
-      return create$2(create$2(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create$2(create$2(l, v, rl.l), rl.v, create$2(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$1(rr) >= height$1(rl)) {
+    return create$2(create$2(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$2(create$2(l, v, rl.l), rl.v, create$2(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -6241,7 +6251,7 @@ function bal$1(l, v, r) {
 }
 
 function add$1(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -6275,7 +6285,7 @@ function add$1(x, t) {
 function mem$1(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.string_compare(x, param.v);
@@ -6288,10 +6298,10 @@ function mem$1(x, _param) {
 }
 
 function height$2(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -6308,26 +6318,28 @@ function create$3(l, x, d, r) {
 }
 
 function bal$2(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$2(ll) >= height$2(lr)) {
-        return create$3(ll, lv, ld, create$3(lr, x, d, r));
-      }
-      if (lr) {
-        return create$3(create$3(ll, lv, ld, lr.l), lr.v, lr.d, create$3(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$2(ll) >= height$2(lr)) {
+      return create$3(ll, lv, ld, create$3(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$3(create$3(ll, lv, ld, lr.l), lr.v, lr.d, create$3(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -6343,23 +6355,23 @@ function bal$2(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$2(rr) >= height$2(rl)) {
-      return create$3(create$3(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create$3(create$3(l, x, d, rl.l), rl.v, rl.d, create$3(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$2(rr) >= height$2(rl)) {
+    return create$3(create$3(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$3(create$3(l, x, d, rl.l), rl.v, rl.d, create$3(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -6368,7 +6380,7 @@ function bal$2(l, x, d, r) {
 }
 
 function add$2(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -6414,18 +6426,18 @@ function add$2(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.string_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.string_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
@@ -6439,16 +6451,18 @@ function compare$1(param, param$1) {
 }
 
 function height$3(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create$4(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -6458,25 +6472,27 @@ function create$4(l, v, r) {
 }
 
 function bal$3(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$3(ll) >= height$3(lr)) {
-        return create$4(ll, lv, create$4(lr, v, r));
-      }
-      if (lr) {
-        return create$4(create$4(ll, lv, lr.l), lr.v, create$4(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$3(ll) >= height$3(lr)) {
+      return create$4(ll, lv, create$4(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$4(create$4(ll, lv, lr.l), lr.v, create$4(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -6491,22 +6507,22 @@ function bal$3(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$3(rr) >= height$3(rl)) {
-      return create$4(create$4(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create$4(create$4(l, v, rl.l), rl.v, create$4(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$3(rr) >= height$3(rl)) {
+    return create$4(create$4(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$4(create$4(l, v, rl.l), rl.v, create$4(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -6515,7 +6531,7 @@ function bal$3(l, v, r) {
 }
 
 function add$3(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -6549,7 +6565,7 @@ function add$3(x, t) {
 function mem$2(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = compare$1(x, param.v);
@@ -6714,49 +6730,29 @@ function param_list_or_type(env) {
   var token$5 = Curry._2(Parser_env_Peek.token, undefined, env);
   var ret;
   var exit = 0;
-  if (typeof token$5 === "number") {
-    if (token$5 !== 105) {
-      if (token$5 >= 12) {
+  if (/* tag */typeof token$5 === "number") {
+    switch (token$5) {
+      case /* T_IDENTIFIER */0 :
+          ret = function_param_or_generic_type(env);
+          break;
+      case /* T_RPAREN */4 :
+          ret = {
+            TAG: /* ParamList */0,
+            _0: [
+              undefined,
+              /* [] */0
+            ]
+          };
+          break;
+      case /* T_ELLIPSIS */11 :
+      case /* T_EOF */105 :
+          ret = {
+            TAG: /* ParamList */0,
+            _0: Curry._2(function_param_list_without_parens, env, /* [] */0)
+          };
+          break;
+      default:
         exit = 1;
-      } else {
-        switch (token$5) {
-          case /* T_IDENTIFIER */0 :
-              ret = function_param_or_generic_type(env);
-              break;
-          case /* T_RPAREN */4 :
-              ret = {
-                TAG: /* ParamList */0,
-                _0: [
-                  undefined,
-                  /* [] */0
-                ]
-              };
-              break;
-          case /* T_LCURLY */1 :
-          case /* T_RCURLY */2 :
-          case /* T_LPAREN */3 :
-          case /* T_LBRACKET */5 :
-          case /* T_RBRACKET */6 :
-          case /* T_SEMICOLON */7 :
-          case /* T_COMMA */8 :
-          case /* T_PERIOD */9 :
-          case /* T_ARROW */10 :
-              exit = 1;
-              break;
-          case /* T_ELLIPSIS */11 :
-              ret = {
-                TAG: /* ParamList */0,
-                _0: Curry._2(function_param_list_without_parens, env, /* [] */0)
-              };
-              break;
-          
-        }
-      }
-    } else {
-      ret = {
-        TAG: /* ParamList */0,
-        _0: Curry._2(function_param_list_without_parens, env, /* [] */0)
-      };
     }
   } else {
     exit = 1;
@@ -6765,7 +6761,26 @@ function param_list_or_type(env) {
     var match = primitive(token$5);
     if (match !== undefined) {
       var match$1 = Curry._2(Parser_env_Peek.token, 1, env);
-      if (typeof match$1 === "number" && (match$1 === 77 || match$1 === 76)) {
+      var exit$1 = 0;
+      if (/* tag */typeof match$1 === "number") {
+        switch (match$1) {
+          case /* T_PLING */76 :
+          case /* T_COLON */77 :
+              exit$1 = 2;
+              break;
+          default:
+            ret = {
+              TAG: /* Type */1,
+              _0: union(env)
+            };
+        }
+      } else {
+        ret = {
+          TAG: /* Type */1,
+          _0: union(env)
+        };
+      }
+      if (exit$1 === 2) {
         var match$2 = Curry._1(Parse.identifier_or_reserved_keyword, env);
         var name = match$2[0];
         if (!env.parse_options.types) {
@@ -6794,12 +6809,8 @@ function param_list_or_type(env) {
                 tl: /* [] */0
               })
         };
-      } else {
-        ret = {
-          TAG: /* Type */1,
-          _0: union(env)
-        };
       }
+      
     } else {
       ret = {
         TAG: /* Type */1,
@@ -6820,22 +6831,29 @@ function function_param_list(env) {
 
 function prefix(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (match !== 76) {
-    var t = primary(env);
-    return postfix_with(env, t);
+  if (/* tag */typeof match !== "number") {
+    return postfix(env);
+  }
+  if (match !== /* T_PLING */76) {
+    return postfix(env);
   }
   var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   token$4(env, /* T_PLING */76);
-  var t$1 = prefix(env);
+  var t = prefix(env);
   return [
-          btwn(loc, t$1[0]),
+          btwn(loc, t[0]),
           {
             TAG: /* Nullable */0,
-            _0: t$1
+            _0: t
           }
         ];
 }
 
+function postfix(env) {
+  var t = primary(env);
+  return postfix_with(env, t);
+}
+
 function intersection(env) {
   maybe(env, /* T_BIT_AND */82);
   var left = prefix(env);
@@ -6929,16 +6947,12 @@ function postfix_with(env, _t) {
 }
 
 function primitive(param) {
-  if (typeof param !== "number") {
-    return ;
-  }
-  if (param === 27) {
-    return /* Null */2;
-  }
-  if (param < 107) {
+  if (/* tag */typeof param !== "number") {
     return ;
   }
   switch (param) {
+    case /* T_NULL */27 :
+        return /* Null */2;
     case /* T_ANY_TYPE */107 :
         return /* Any */0;
     case /* T_BOOLEAN_TYPE */108 :
@@ -6949,35 +6963,52 @@ function primitive(param) {
         return /* String */4;
     case /* T_VOID_TYPE */111 :
         return /* Void */1;
-    
+    default:
+      return ;
   }
 }
 
 function function_param_or_generic_type(env) {
   var id = Curry._2(Parse.identifier, undefined, env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match === "number" && (match === 77 || match === 76)) {
-    var param = function_param_with_id(env, id);
-    maybe(env, /* T_COMMA */8);
-    return {
-            TAG: /* ParamList */0,
-            _0: Curry._2(function_param_list_without_parens, env, {
-                  hd: param,
-                  tl: /* [] */0
-                })
-          };
+  var exit = 0;
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_PLING */76 :
+      case /* T_COLON */77 :
+          exit = 2;
+          break;
+      default:
+        exit = 1;
+    }
+  } else {
+    exit = 1;
+  }
+  switch (exit) {
+    case 1 :
+        return {
+                TAG: /* Type */1,
+                _0: Curry._2(union_with, env, Curry._2(intersection_with, env, postfix_with(env, generic_type_with_identifier(env, id))))
+              };
+    case 2 :
+        var param = function_param_with_id(env, id);
+        maybe(env, /* T_COMMA */8);
+        return {
+                TAG: /* ParamList */0,
+                _0: Curry._2(function_param_list_without_parens, env, {
+                      hd: param,
+                      tl: /* [] */0
+                    })
+              };
+    
   }
-  return {
-          TAG: /* Type */1,
-          _0: Curry._2(union_with, env, Curry._2(intersection_with, env, postfix_with(env, generic_type_with_identifier(env, id))))
-        };
 }
 
 function primary(env) {
   var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var token$5 = Curry._2(Parser_env_Peek.token, undefined, env);
   var exit = 0;
-  if (typeof token$5 === "number") {
+  if (/* tag */typeof token$5 === "number") {
     switch (token$5) {
       case /* T_IDENTIFIER */0 :
           var match = generic(env);
@@ -7229,30 +7260,58 @@ function params(env, allow_default, _require_default, _acc) {
     var acc = _acc;
     var require_default = _require_default;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    var variance = typeof match === "number" ? (
-        match !== 94 ? (
-            match !== 95 ? undefined : (token$3(env), /* Minus */1)
-          ) : (token$3(env), /* Plus */0)
-      ) : undefined;
+    var variance;
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_PLUS */94 :
+            token$3(env);
+            variance = /* Plus */0;
+            break;
+        case /* T_MINUS */95 :
+            token$3(env);
+            variance = /* Minus */1;
+            break;
+        default:
+          variance = undefined;
+      }
+    } else {
+      variance = undefined;
+    }
     var match$1 = Curry._2(Parse.identifier_with_type, env, /* StrictParamName */28);
     var id = match$1[1];
     var loc = match$1[0];
     var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
-    var match$3 = allow_default ? (
-        match$2 === 75 ? (token$3(env), [
-              union(env),
-              true
-            ]) : (require_default ? error_at(env, [
-                    loc,
-                    /* MissingTypeParamDefault */58
-                  ]) : undefined, [
-              undefined,
-              require_default
-            ])
-      ) : [
+    var match$3;
+    if (allow_default) {
+      var exit = 0;
+      if (/* tag */typeof match$2 === "number" && match$2 === /* T_ASSIGN */75) {
+        token$3(env);
+        match$3 = [
+          union(env),
+          true
+        ];
+      } else {
+        exit = 1;
+      }
+      if (exit === 1) {
+        if (require_default) {
+          error_at(env, [
+                loc,
+                /* MissingTypeParamDefault */58
+              ]);
+        }
+        match$3 = [
+          undefined,
+          require_default
+        ];
+      }
+      
+    } else {
+      match$3 = [
         undefined,
         false
       ];
+    }
     var param_1 = {
       name: id.name,
       bound: id.typeAnnotation,
@@ -7268,14 +7327,14 @@ function params(env, allow_default, _require_default, _acc) {
       tl: acc
     };
     var match$4 = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match$4 === "number") {
-      if (match$4 === 90) {
-        return List.rev(acc$1);
-      }
-      if (match$4 === 105) {
-        return List.rev(acc$1);
+    if (/* tag */typeof match$4 === "number") {
+      switch (match$4) {
+        case /* T_GREATER_THAN */90 :
+        case /* T_EOF */105 :
+            return List.rev(acc$1);
+        default:
+          
       }
-      
     }
     token$4(env, /* T_COMMA */8);
     if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_GREATER_THAN */90) {
@@ -7316,7 +7375,7 @@ function union_with(env, left) {
     while(true) {
       var acc = _acc;
       var match = Curry._2(Parser_env_Peek.token, undefined, env);
-      if (match === 80) {
+      if (/* tag */typeof match === "number" && match === /* T_BIT_OR */80) {
         token$4(env, /* T_BIT_OR */80);
         _acc = {
           hd: intersection(env),
@@ -7350,13 +7409,19 @@ function function_param_list_without_parens(env) {
       var acc = _acc;
       var t = Curry._2(Parser_env_Peek.token, undefined, env);
       var exit = 0;
-      exit = typeof t === "number" ? (
-          t > 11 || t < 4 ? (
-              t !== 105 ? 1 : 2
-            ) : (
-              t > 10 || t < 5 ? 2 : 1
-            )
-        ) : 1;
+      if (/* tag */typeof t === "number") {
+        switch (t) {
+          case /* T_RPAREN */4 :
+          case /* T_ELLIPSIS */11 :
+          case /* T_EOF */105 :
+              exit = 2;
+              break;
+          default:
+            exit = 1;
+        }
+      } else {
+        exit = 1;
+      }
       switch (exit) {
         case 1 :
             var acc_0 = param(env);
@@ -7390,7 +7455,7 @@ function intersection_with(env, left) {
     while(true) {
       var acc = _acc;
       var match = Curry._2(Parser_env_Peek.token, undefined, env);
-      if (match === 82) {
+      if (/* tag */typeof match === "number" && match === /* T_BIT_AND */82) {
         token$4(env, /* T_BIT_AND */82);
         _acc = {
           hd: prefix(env),
@@ -7416,14 +7481,14 @@ function types(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 6) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RBRACKET */6 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var acc_0 = union(env);
     var acc$1 = {
@@ -7529,20 +7594,17 @@ function indexer_property(env, start_loc, $$static) {
 
 function semicolon$1(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match === "number") {
-    if (match >= 7) {
-      if (match >= 9) {
-        return error_unexpected(env);
-      } else {
+  if (/* tag */typeof match !== "number") {
+    return error_unexpected(env);
+  }
+  switch (match) {
+    case /* T_RCURLY */2 :
+        return ;
+    case /* T_SEMICOLON */7 :
+    case /* T_COMMA */8 :
         return token$3(env);
-      }
-    } else if (match !== 2) {
+    default:
       return error_unexpected(env);
-    } else {
-      return ;
-    }
-  } else {
-    return error_unexpected(env);
   }
 }
 
@@ -7556,44 +7618,30 @@ function properties(allow_static, env, _param) {
     var $$static = allow_static && maybe(env, /* T_STATIC */40);
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
     var exit = 0;
-    if (typeof match === "number") {
-      if (match !== 89) {
-        if (match !== 105) {
-          if (match >= 6) {
-            exit = 1;
-          } else {
-            switch (match) {
-              case /* T_RCURLY */2 :
-                  exit = 2;
-                  break;
-              case /* T_LPAREN */3 :
-                  exit = 3;
-                  break;
-              case /* T_IDENTIFIER */0 :
-              case /* T_LCURLY */1 :
-              case /* T_RPAREN */4 :
-                  exit = 1;
-                  break;
-              case /* T_LBRACKET */5 :
-                  var indexer = indexer_property(env, start_loc, $$static);
-                  semicolon$1(env);
-                  _param = [
-                    acc,
-                    {
-                      hd: indexer,
-                      tl: indexers
-                    },
-                    callProperties
-                  ];
-                  continue ;
-              
-            }
-          }
-        } else {
-          exit = 2;
-        }
-      } else {
-        exit = 3;
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_LBRACKET */5 :
+            var indexer = indexer_property(env, start_loc, $$static);
+            semicolon$1(env);
+            _param = [
+              acc,
+              {
+                hd: indexer,
+                tl: indexers
+              },
+              callProperties
+            ];
+            continue ;
+        case /* T_LPAREN */3 :
+        case /* T_LESS_THAN */89 :
+            exit = 3;
+            break;
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            exit = 2;
+            break;
+        default:
+          exit = 1;
       }
     } else {
       exit = 1;
@@ -7603,7 +7651,7 @@ function properties(allow_static, env, _param) {
           var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
           var match$2;
           var exit$1 = 0;
-          if ($$static && match$1 === 77) {
+          if ($$static && /* tag */typeof match$1 === "number" && match$1 === /* T_COLON */77) {
             strict_error_at(env, [
                   start_loc,
                   /* StrictReservedWord */39
@@ -7642,7 +7690,19 @@ function properties(allow_static, env, _param) {
           var key$1 = match$2[1][1];
           var $$static$1 = match$2[0];
           var match$3 = Curry._2(Parser_env_Peek.token, undefined, env);
-          var property$1 = typeof match$3 === "number" && !(match$3 !== 3 && match$3 !== 89) ? method_property(env, start_loc, $$static$1, key$1) : property(env, start_loc, $$static$1, key$1);
+          var property$1;
+          if (/* tag */typeof match$3 === "number") {
+            switch (match$3) {
+              case /* T_LPAREN */3 :
+              case /* T_LESS_THAN */89 :
+                  property$1 = method_property(env, start_loc, $$static$1, key$1);
+                  break;
+              default:
+                property$1 = property(env, start_loc, $$static$1, key$1);
+            }
+          } else {
+            property$1 = property(env, start_loc, $$static$1, key$1);
+          }
           semicolon$1(env);
           _param = [
             {
@@ -7701,14 +7761,14 @@ function params$1(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 90) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_GREATER_THAN */90 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var acc_0 = union(env);
     var acc$1 = {
@@ -7772,7 +7832,7 @@ function annotation(env) {
 
 function annotation_opt(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (match === 77) {
+  if (/* tag */typeof match === "number" && match === /* T_COLON */77) {
     return annotation(env);
   }
   
@@ -7953,13 +8013,19 @@ function param_list(env, _param) {
     var params = param$2[0];
     var t = Curry._2(Parser_env_Peek.token, undefined, env);
     var exit = 0;
-    exit = typeof t === "number" ? (
-        t > 11 || t < 4 ? (
-            t !== 105 ? 1 : 2
-          ) : (
-            t > 10 || t < 5 ? 2 : 1
-          )
-      ) : 1;
+    if (/* tag */typeof t === "number") {
+      switch (t) {
+        case /* T_RPAREN */4 :
+        case /* T_ELLIPSIS */11 :
+        case /* T_EOF */105 :
+            exit = 2;
+            break;
+        default:
+          exit = 1;
+      }
+    } else {
+      exit = 1;
+    }
     switch (exit) {
       case 1 :
           var match = param$1(env);
@@ -8062,23 +8128,24 @@ function _function(env) {
   var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
   var match$2;
   var exit = 0;
-  if (match && typeof match$1 === "number") {
-    if (match$1 !== 3) {
-      if (match$1 !== 89) {
+  if (match && /* tag */typeof match$1 === "number") {
+    switch (match$1) {
+      case /* T_LPAREN */3 :
+          match$2 = [
+            undefined,
+            undefined
+          ];
+          break;
+      case /* T_LESS_THAN */89 :
+          var typeParams = Curry._1(type_parameter_declaration$1, env);
+          var id = Curry._2(Parser_env_Peek.token, undefined, env) === /* T_LPAREN */3 ? undefined : Curry._2(Parse.identifier, /* StrictFunctionName */30, env);
+          match$2 = [
+            typeParams,
+            id
+          ];
+          break;
+      default:
         exit = 1;
-      } else {
-        var typeParams = Curry._1(type_parameter_declaration$1, env);
-        var id = Curry._2(Parser_env_Peek.token, undefined, env) === /* T_LPAREN */3 ? undefined : Curry._2(Parse.identifier, /* StrictFunctionName */30, env);
-        match$2 = [
-          typeParams,
-          id
-        ];
-      }
-    } else {
-      match$2 = [
-        undefined,
-        undefined
-      ];
     }
   } else {
     exit = 1;
@@ -8248,16 +8315,11 @@ function variable(env) {
   var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var match$1;
-  if (typeof match === "number") {
+  if (/* tag */typeof match === "number") {
     switch (match) {
       case /* T_VAR */22 :
           match$1 = declarations(/* T_VAR */22, /* Var */0, env);
           break;
-      case /* T_WHILE */23 :
-      case /* T_WITH */24 :
-          error_unexpected(env);
-          match$1 = declarations(/* T_VAR */22, /* Var */0, env);
-          break;
       case /* T_CONST */25 :
           match$1 = $$const(env);
           break;
@@ -8293,7 +8355,7 @@ function is_tighter(a, b) {
 
 function is_lhs(param) {
   var tmp = param[1];
-  if (typeof tmp === "number") {
+  if (/* tag */typeof tmp === "number") {
     return false;
   }
   switch (tmp.TAG | 0) {
@@ -8307,7 +8369,7 @@ function is_lhs(param) {
 
 function is_assignable_lhs(param) {
   var tmp = param[1];
-  if (typeof tmp === "number") {
+  if (/* tag */typeof tmp === "number") {
     return false;
   }
   switch (tmp.TAG | 0) {
@@ -8324,7 +8386,7 @@ function is_assignable_lhs(param) {
 function assignment_op(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var op;
-  if (typeof match === "number") {
+  if (/* tag */typeof match === "number") {
     switch (match) {
       case /* T_RSHIFT3_ASSIGN */63 :
           op = /* RShift3Assign */9;
@@ -8404,49 +8466,32 @@ function conditional(env) {
 
 function peek_unary_op(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number") {
+  if (/* tag */typeof match !== "number") {
     return ;
   }
-  if (match >= 46) {
-    if (match < 94) {
-      if (match !== 62 || !env.allow_await) {
-        return ;
-      } else {
-        return /* Await */7;
-      }
-    }
-    if (match >= 102) {
-      return ;
-    }
-    switch (match) {
-      case /* T_PLUS */94 :
-          return /* Plus */1;
-      case /* T_MINUS */95 :
-          return /* Minus */0;
-      case /* T_DIV */96 :
-      case /* T_MULT */97 :
-      case /* T_EXP */98 :
-      case /* T_MOD */99 :
+  switch (match) {
+    case /* T_DELETE */43 :
+        return /* Delete */6;
+    case /* T_TYPEOF */44 :
+        return /* Typeof */4;
+    case /* T_VOID */45 :
+        return /* Void */5;
+    case /* T_AWAIT */62 :
+        if (env.allow_await) {
+          return /* Await */7;
+        } else {
           return ;
-      case /* T_NOT */100 :
-          return /* Not */2;
-      case /* T_BIT_NOT */101 :
-          return /* BitNot */3;
-      
-    }
-  } else {
-    if (match < 43) {
+        }
+    case /* T_PLUS */94 :
+        return /* Plus */1;
+    case /* T_MINUS */95 :
+        return /* Minus */0;
+    case /* T_NOT */100 :
+        return /* Not */2;
+    case /* T_BIT_NOT */101 :
+        return /* BitNot */3;
+    default:
       return ;
-    }
-    switch (match) {
-      case /* T_DELETE */43 :
-          return /* Delete */6;
-      case /* T_TYPEOF */44 :
-          return /* Typeof */4;
-      case /* T_VOID */45 :
-          return /* Void */5;
-      
-    }
   }
 }
 
@@ -8457,9 +8502,9 @@ function unary(env) {
     token$3(env);
     var argument = unary(env);
     var loc = btwn(begin_loc, argument[0]);
-    if (op === 6) {
+    if (op === /* Delete */6) {
       var tmp = argument[1];
-      if (typeof tmp !== "number" && tmp.TAG === /* Identifier */18) {
+      if (/* tag */typeof tmp !== "number" && tmp.TAG === /* Identifier */18) {
         strict_error_at(env, [
               loc,
               /* StrictDelete */32
@@ -8480,22 +8525,42 @@ function unary(env) {
           ];
   }
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  var op$1 = typeof match === "number" ? (
-      match !== 102 ? (
-          match !== 103 ? undefined : /* Decrement */1
-        ) : /* Increment */0
-    ) : undefined;
+  var op$1;
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_INCR */102 :
+          op$1 = /* Increment */0;
+          break;
+      case /* T_DECR */103 :
+          op$1 = /* Decrement */1;
+          break;
+      default:
+        op$1 = undefined;
+    }
+  } else {
+    op$1 = undefined;
+  }
   if (op$1 === undefined) {
     var argument$1 = left_hand_side(env);
     if (Curry._1(Parser_env_Peek.is_line_terminator, env)) {
       return argument$1;
     }
     var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
-    var op$2 = typeof match$1 === "number" ? (
-        match$1 !== 102 ? (
-            match$1 !== 103 ? undefined : /* Decrement */1
-          ) : /* Increment */0
-      ) : undefined;
+    var op$2;
+    if (/* tag */typeof match$1 === "number") {
+      switch (match$1) {
+        case /* T_INCR */102 :
+            op$2 = /* Increment */0;
+            break;
+        case /* T_DECR */103 :
+            op$2 = /* Decrement */1;
+            break;
+        default:
+          op$2 = undefined;
+      }
+    } else {
+      op$2 = undefined;
+    }
     if (op$2 === undefined) {
       return argument$1;
     }
@@ -8506,7 +8571,7 @@ function unary(env) {
           ]);
     }
     var match$2 = argument$1[1];
-    if (typeof match$2 !== "number" && match$2.TAG === /* Identifier */18) {
+    if (/* tag */typeof match$2 !== "number" && match$2.TAG === /* Identifier */18) {
       if (is_restricted(match$2._0[1].name)) {
         strict_error(env, /* StrictLHSPostfix */37);
       }
@@ -8535,7 +8600,7 @@ function unary(env) {
         ]);
   }
   var match$3 = argument$2[1];
-  if (typeof match$3 !== "number" && match$3.TAG === /* Identifier */18) {
+  if (/* tag */typeof match$3 !== "number" && match$3.TAG === /* Identifier */18) {
     if (is_restricted(match$3._0[1].name)) {
       strict_error(env, /* StrictLHSPrefix */38);
     }
@@ -8556,14 +8621,21 @@ function unary(env) {
 
 function left_hand_side(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  var expr = match === 42 ? _new(env, (function (new_expr, _args) {
+  var expr;
+  var exit = 0;
+  if (/* tag */typeof match === "number" && match === /* T_NEW */42) {
+    expr = _new(env, (function (new_expr, _args) {
             return new_expr;
-          })) : (
-      Curry._2(Parser_env_Peek.is_function, undefined, env) ? _function$1(env) : primary$1(env)
-    );
+          }));
+  } else {
+    exit = 1;
+  }
+  if (exit === 1) {
+    expr = Curry._2(Parser_env_Peek.is_function, undefined, env) ? _function$1(env) : primary$1(env);
+  }
   var expr$1 = member(env, expr);
   var part = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof part === "number") {
+  if (/* tag */typeof part === "number") {
     if (part === /* T_LPAREN */3) {
       return call(env, expr$1);
     } else {
@@ -8580,7 +8652,7 @@ function call(env, _left) {
   while(true) {
     var left = _left;
     var part = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof part !== "number") {
+    if (/* tag */typeof part !== "number") {
       if (part.TAG === /* T_TEMPLATE_PART */2) {
         return tagged_template(env, left, part._0);
       } else {
@@ -8654,7 +8726,7 @@ function _new(env, _finish_fn) {
   while(true) {
     var finish_fn = _finish_fn;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match === 42) {
+    if (/* tag */typeof match === "number" && match === /* T_NEW */42) {
       var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
       token$4(env, /* T_NEW */42);
       var finish_fn$p = (function(finish_fn,start_loc){
@@ -8689,58 +8761,60 @@ function _new(env, _finish_fn) {
     var callee = member(with_no_call(true, env), expr);
     var part = Curry._2(Parser_env_Peek.token, undefined, env);
     var callee$1;
-    callee$1 = typeof part === "number" || part.TAG !== /* T_TEMPLATE_PART */2 ? callee : tagged_template(env, callee, part._0);
+    callee$1 = /* tag */typeof part === "number" || part.TAG !== /* T_TEMPLATE_PART */2 ? callee : tagged_template(env, callee, part._0);
     var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
-    var args = match$1 === 3 ? Curry._1($$arguments, env) : undefined;
+    var args;
+    args = /* tag */typeof match$1 === "number" && match$1 === /* T_LPAREN */3 ? Curry._1($$arguments, env) : undefined;
     return Curry._2(finish_fn, callee$1, args);
   };
 }
 
 function member(env, left) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number") {
+  if (/* tag */typeof match !== "number") {
     return left;
   }
-  if (match !== 5) {
-    if (match !== 9) {
+  switch (match) {
+    case /* T_LBRACKET */5 :
+        token$4(env, /* T_LBRACKET */5);
+        var expr = Curry._1(Parse.expression, with_no_call(false, env));
+        var last_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+        token$4(env, /* T_RBRACKET */6);
+        return call(env, [
+                    btwn(left[0], last_loc),
+                    {
+                      TAG: /* Member */13,
+                      _0: {
+                        _object: left,
+                        property: {
+                          TAG: /* PropertyExpression */1,
+                          _0: expr
+                        },
+                        computed: true
+                      }
+                    }
+                  ]);
+    case /* T_PERIOD */9 :
+        token$4(env, /* T_PERIOD */9);
+        var match$1 = identifier_or_reserved_keyword(env);
+        var id = match$1[0];
+        return call(env, [
+                    btwn(left[0], id[0]),
+                    {
+                      TAG: /* Member */13,
+                      _0: {
+                        _object: left,
+                        property: {
+                          TAG: /* PropertyIdentifier */0,
+                          _0: id
+                        },
+                        computed: false
+                      }
+                    }
+                  ]);
+    default:
       return left;
-    }
-    token$4(env, /* T_PERIOD */9);
-    var match$1 = identifier_or_reserved_keyword(env);
-    var id = match$1[0];
-    return call(env, [
-                btwn(left[0], id[0]),
-                {
-                  TAG: /* Member */13,
-                  _0: {
-                    _object: left,
-                    property: {
-                      TAG: /* PropertyIdentifier */0,
-                      _0: id
-                    },
-                    computed: false
-                  }
-                }
-              ]);
   }
-  token$4(env, /* T_LBRACKET */5);
-  var expr = Curry._1(Parse.expression, with_no_call(false, env));
-  var last_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-  token$4(env, /* T_RBRACKET */6);
-  return call(env, [
-              btwn(left[0], last_loc),
-              {
-                TAG: /* Member */13,
-                _0: {
-                  _object: left,
-                  property: {
-                    TAG: /* PropertyExpression */1,
-                    _0: expr
-                  },
-                  computed: true
-                }
-              }
-            ]);
 }
 
 function _function$1(env) {
@@ -8756,7 +8830,8 @@ function _function$1(env) {
     ];
   } else {
     var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
-    var id = match$1 === 89 ? undefined : Curry._2(Parse.identifier, /* StrictFunctionName */30, env);
+    var id;
+    id = /* tag */typeof match$1 === "number" && match$1 === /* T_LESS_THAN */89 ? undefined : Curry._2(Parse.identifier, /* StrictFunctionName */30, env);
     match = [
       id,
       Curry._1(type_parameter_declaration$1, env)
@@ -8799,32 +8874,29 @@ function _function$1(env) {
 function number(env, number_type) {
   var value = Curry._2(Parser_env_Peek.value, undefined, env);
   var value$1;
-  if (number_type !== 0) {
-    switch (number_type) {
-      case /* LEGACY_OCTAL */1 :
-          strict_error(env, /* StrictOctalLiteral */31);
-          value$1 = Caml_format.int_of_string("0o" + value);
-          break;
-      case /* OCTAL */2 :
-          value$1 = Caml_format.int_of_string(value);
-          break;
-      case /* NORMAL */3 :
-          try {
-            value$1 = float_of_string(value);
-          }
-          catch (exn){
-            if (Sys.win32) {
-              error(env, /* WindowsFloatOfString */59);
-              value$1 = 789.0;
-            } else {
-              throw exn;
-            }
+  switch (number_type) {
+    case /* LEGACY_OCTAL */1 :
+        strict_error(env, /* StrictOctalLiteral */31);
+        value$1 = Caml_format.int_of_string("0o" + value);
+        break;
+    case /* BINARY */0 :
+    case /* OCTAL */2 :
+        value$1 = Caml_format.int_of_string(value);
+        break;
+    case /* NORMAL */3 :
+        try {
+          value$1 = float_of_string(value);
+        }
+        catch (exn){
+          if (Sys.win32) {
+            error(env, /* WindowsFloatOfString */59);
+            value$1 = 789.0;
+          } else {
+            throw exn;
           }
-          break;
-      
-    }
-  } else {
-    value$1 = Caml_format.int_of_string(value);
+        }
+        break;
+    
   }
   token$4(env, {
         TAG: /* T_NUMBER */0,
@@ -8837,7 +8909,7 @@ function primary$1(env) {
   var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var number_type = Curry._2(Parser_env_Peek.token, undefined, env);
   var exit = 0;
-  if (typeof number_type === "number") {
+  if (/* tag */typeof number_type === "number") {
     switch (number_type) {
       case /* T_LCURLY */1 :
           var match = Curry._1(Parse.object_initializer, env);
@@ -8853,28 +8925,29 @@ function primary$1(env) {
           var expression = Curry._1(assignment, env);
           var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
           var ret;
-          if (typeof match$1 === "number") {
-            if (match$1 !== 8) {
-              if (match$1 !== 77) {
-                ret = expression;
-              } else {
-                var typeAnnotation = wrap(annotation, env);
-                ret = [
-                  btwn(expression[0], typeAnnotation[0]),
-                  {
-                    TAG: /* TypeCast */24,
-                    _0: {
-                      expression: expression,
-                      typeAnnotation: typeAnnotation
+          if (/* tag */typeof match$1 === "number") {
+            switch (match$1) {
+              case /* T_COMMA */8 :
+                  ret = sequence(env, {
+                        hd: expression,
+                        tl: /* [] */0
+                      });
+                  break;
+              case /* T_COLON */77 :
+                  var typeAnnotation = wrap(annotation, env);
+                  ret = [
+                    btwn(expression[0], typeAnnotation[0]),
+                    {
+                      TAG: /* TypeCast */24,
+                      _0: {
+                        expression: expression,
+                        typeAnnotation: typeAnnotation
+                      }
                     }
-                  }
-                ];
-              }
-            } else {
-              ret = sequence(env, {
-                    hd: expression,
-                    tl: /* [] */0
-                  });
+                  ];
+                  break;
+              default:
+                ret = expression;
             }
           } else {
             ret = expression;
@@ -8949,7 +9022,7 @@ function primary$1(env) {
           var loc$2 = Curry._2(Parser_env_Peek.loc, undefined, env);
           var match$4 = Curry._2(Parser_env_Peek.token, undefined, env);
           var match$5;
-          if (typeof match$4 === "number") {
+          if (/* tag */typeof match$4 === "number") {
             throw {
                   RE_EXN_ID: "Assert_failure",
                   _1: [
@@ -9162,7 +9235,7 @@ function sequence(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match === 8) {
+    if (/* tag */typeof match === "number" && match === /* T_COMMA */8) {
       token$4(env, /* T_COMMA */8);
       var expr = Curry._1(assignment, env);
       _acc = {
@@ -9191,87 +9264,132 @@ function identifier_or_reserved_keyword(env) {
   var lex_value = Curry._2(Parser_env_Peek.value, undefined, env);
   var lex_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var exit = 0;
-  if (typeof lex_token === "number") {
-    if (lex_token >= 58) {
-      if (lex_token < 62) {
-        return [
-                Curry._2(Parse.identifier, undefined, env),
-                undefined
-              ];
-      }
-      exit = 1;
-    } else {
-      if (lex_token === 0) {
-        return [
-                Curry._2(Parse.identifier, undefined, env),
-                undefined
-              ];
-      }
-      exit = 1;
+  if (/* tag */typeof lex_token === "number") {
+    switch (lex_token) {
+      case /* T_IDENTIFIER */0 :
+      case /* T_DECLARE */58 :
+      case /* T_TYPE */59 :
+      case /* T_OF */60 :
+      case /* T_ASYNC */61 :
+          exit = 2;
+          break;
+      default:
+        exit = 1;
     }
   } else {
     exit = 1;
   }
-  if (exit === 1) {
-    var err;
-    var exit$1 = 0;
-    if (typeof lex_token === "number") {
-      if (lex_token > 106 || lex_token < 58) {
-        if (lex_token >= 13) {
-          exit$1 = 2;
-        } else {
-          error_unexpected(env);
-          err = undefined;
-        }
-      } else if (lex_token !== 62) {
-        error_unexpected(env);
-        err = undefined;
-      } else {
-        exit$1 = 2;
-      }
-    } else {
-      error_unexpected(env);
-      err = undefined;
-    }
-    if (exit$1 === 2) {
-      err = [
-        lex_loc,
-        get_unexpected_error([
-              lex_token,
-              lex_value
-            ])
-      ];
-    }
-    token$3(env);
-    return [
-            [
-              lex_loc,
-              {
-                name: lex_value,
-                typeAnnotation: undefined,
-                optional: false
-              }
-            ],
-            err
-          ];
-  }
-  
-}
-
-function assignment_but_not_arrow_function(env) {
-  var expr = conditional(env);
-  var operator = assignment_op(env);
-  if (operator === undefined) {
-    return expr;
-  }
-  if (!is_assignable_lhs(expr)) {
-    error_at(env, [
+  switch (exit) {
+    case 1 :
+        var err;
+        var exit$1 = 0;
+        if (/* tag */typeof lex_token === "number") {
+          switch (lex_token) {
+            case /* T_FUNCTION */13 :
+            case /* T_IF */14 :
+            case /* T_IN */15 :
+            case /* T_INSTANCEOF */16 :
+            case /* T_RETURN */17 :
+            case /* T_SWITCH */18 :
+            case /* T_THIS */19 :
+            case /* T_THROW */20 :
+            case /* T_TRY */21 :
+            case /* T_VAR */22 :
+            case /* T_WHILE */23 :
+            case /* T_WITH */24 :
+            case /* T_CONST */25 :
+            case /* T_LET */26 :
+            case /* T_NULL */27 :
+            case /* T_FALSE */28 :
+            case /* T_TRUE */29 :
+            case /* T_BREAK */30 :
+            case /* T_CASE */31 :
+            case /* T_CATCH */32 :
+            case /* T_CONTINUE */33 :
+            case /* T_DEFAULT */34 :
+            case /* T_DO */35 :
+            case /* T_FINALLY */36 :
+            case /* T_FOR */37 :
+            case /* T_CLASS */38 :
+            case /* T_EXTENDS */39 :
+            case /* T_STATIC */40 :
+            case /* T_ELSE */41 :
+            case /* T_NEW */42 :
+            case /* T_DELETE */43 :
+            case /* T_TYPEOF */44 :
+            case /* T_VOID */45 :
+            case /* T_ENUM */46 :
+            case /* T_EXPORT */47 :
+            case /* T_IMPORT */48 :
+            case /* T_SUPER */49 :
+            case /* T_IMPLEMENTS */50 :
+            case /* T_INTERFACE */51 :
+            case /* T_PACKAGE */52 :
+            case /* T_PRIVATE */53 :
+            case /* T_PROTECTED */54 :
+            case /* T_PUBLIC */55 :
+            case /* T_YIELD */56 :
+            case /* T_DEBUGGER */57 :
+            case /* T_AWAIT */62 :
+            case /* T_ANY_TYPE */107 :
+            case /* T_BOOLEAN_TYPE */108 :
+            case /* T_NUMBER_TYPE */109 :
+            case /* T_STRING_TYPE */110 :
+            case /* T_VOID_TYPE */111 :
+                exit$1 = 3;
+                break;
+            default:
+              error_unexpected(env);
+              err = undefined;
+          }
+        } else {
+          error_unexpected(env);
+          err = undefined;
+        }
+        if (exit$1 === 3) {
+          err = [
+            lex_loc,
+            get_unexpected_error([
+                  lex_token,
+                  lex_value
+                ])
+          ];
+        }
+        token$3(env);
+        return [
+                [
+                  lex_loc,
+                  {
+                    name: lex_value,
+                    typeAnnotation: undefined,
+                    optional: false
+                  }
+                ],
+                err
+              ];
+    case 2 :
+        return [
+                Curry._2(Parse.identifier, undefined, env),
+                undefined
+              ];
+    
+  }
+}
+
+function assignment_but_not_arrow_function(env) {
+  var expr = conditional(env);
+  var operator = assignment_op(env);
+  if (operator === undefined) {
+    return expr;
+  }
+  if (!is_assignable_lhs(expr)) {
+    error_at(env, [
           expr[0],
           /* InvalidLHSInAssignment */14
         ]);
   }
   var match = expr[1];
-  if (typeof match !== "number" && match.TAG === /* Identifier */18) {
+  if (/* tag */typeof match !== "number" && match.TAG === /* Identifier */18) {
     if (is_restricted(match._0[1].name)) {
       strict_error_at(env, [
             expr[0],
@@ -9307,20 +9425,16 @@ function try_assignment_but_not_arrow_function(env) {
   var env$1 = with_error_callback(error_callback, env);
   var ret = assignment_but_not_arrow_function(env$1);
   var match = Curry._2(Parser_env_Peek.token, undefined, env$1);
-  if (typeof match === "number") {
-    if (match !== 10) {
-      if (match === 77) {
-        throw {
-              RE_EXN_ID: Parser_env_Try.Rollback,
-              Error: new Error()
-            };
-      }
-      
-    } else {
-      throw {
-            RE_EXN_ID: Parser_env_Try.Rollback,
-            Error: new Error()
-          };
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_ARROW */10 :
+      case /* T_COLON */77 :
+          throw {
+                RE_EXN_ID: Parser_env_Try.Rollback,
+                Error: new Error()
+              };
+      default:
+        
     }
   }
   if (!Curry._2(Parser_env_Peek.is_identifier, undefined, env$1)) {
@@ -9333,7 +9447,7 @@ function try_assignment_but_not_arrow_function(env) {
         };
   }
   var match$1 = ret[1];
-  if (typeof match$1 === "number") {
+  if (/* tag */typeof match$1 === "number") {
     return ret;
   }
   if (match$1.TAG !== /* Identifier */18) {
@@ -9355,45 +9469,45 @@ function assignment(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var match$1 = Curry._2(Parser_env_Peek.is_identifier, undefined, env);
   var exit = 0;
-  if (typeof match === "number") {
-    if (match > 88 || match < 4) {
-      if (match > 89 || match < 3) {
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_YIELD */56 :
+          if (env.allow_yield) {
+            var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_YIELD */56);
+            if (!env.allow_yield) {
+              error(env, /* IllegalYield */24);
+            }
+            var delegate = maybe(env, /* T_MULT */97);
+            var has_argument = !(Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env));
+            var argument = delegate || has_argument ? Curry._1(assignment, env) : undefined;
+            var end_loc;
+            if (argument !== undefined) {
+              end_loc = argument[0];
+            } else {
+              var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+              var end_loc$1 = loc !== undefined ? loc : start_loc;
+              semicolon(env);
+              end_loc = end_loc$1;
+            }
+            return [
+                    btwn(start_loc, end_loc),
+                    {
+                      TAG: /* Yield */14,
+                      _0: {
+                        argument: argument,
+                        delegate: delegate
+                      }
+                    }
+                  ];
+          }
+          exit = 2;
+          break;
+      case /* T_LPAREN */3 :
+      case /* T_LESS_THAN */89 :
+          break;
+      default:
         exit = 2;
-      }
-      
-    } else if (match !== 56) {
-      exit = 2;
-    } else {
-      if (env.allow_yield) {
-        var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-        token$4(env, /* T_YIELD */56);
-        if (!env.allow_yield) {
-          error(env, /* IllegalYield */24);
-        }
-        var delegate = maybe(env, /* T_MULT */97);
-        var has_argument = !(Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env));
-        var argument = delegate || has_argument ? Curry._1(assignment, env) : undefined;
-        var end_loc;
-        if (argument !== undefined) {
-          end_loc = argument[0];
-        } else {
-          var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-          var end_loc$1 = loc !== undefined ? loc : start_loc;
-          semicolon(env);
-          end_loc = end_loc$1;
-        }
-        return [
-                btwn(start_loc, end_loc),
-                {
-                  TAG: /* Yield */14,
-                  _0: {
-                    argument: argument,
-                    delegate: delegate
-                  }
-                }
-              ];
-      }
-      exit = 2;
     }
   } else {
     exit = 2;
@@ -9402,14 +9516,14 @@ function assignment(env) {
     return assignment_but_not_arrow_function(env);
   }
   var expr = Curry._2(Parser_env_Try.to_parse, env, try_assignment_but_not_arrow_function);
-  if (expr) {
+  if (/* tag */typeof expr !== "number") {
     return expr._0;
   }
   var expr$1 = Curry._2(Parser_env_Try.to_parse, env, try_arrow_function);
-  if (expr$1) {
-    return expr$1._0;
-  } else {
+  if (/* tag */typeof expr$1 === "number") {
     return assignment_but_not_arrow_function(env);
+  } else {
+    return expr$1._0;
   }
 }
 
@@ -9432,7 +9546,13 @@ function logical_and(env, _left, _lloc) {
     var lloc = _lloc;
     var left = _left;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 79) {
+    if (/* tag */typeof match !== "number") {
+      return [
+              lloc,
+              left
+            ];
+    }
+    if (match !== /* T_AND */79) {
       return [
               lloc,
               left
@@ -9452,7 +9572,13 @@ function logical_or(env, _left, _lloc) {
     var lloc = _lloc;
     var left = _left;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 78) {
+    if (/* tag */typeof match !== "number") {
+      return [
+              lloc,
+              left
+            ];
+    }
+    if (match !== /* T_OR */78) {
       return [
               lloc,
               left
@@ -9477,223 +9603,208 @@ function logical(env) {
 function binary_op(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var ret;
-  if (typeof match === "number") {
-    if (match === 16 || match === 15) {
-      ret = match >= 16 ? [
-          /* Instanceof */21,
-          {
-            TAG: /* Left_assoc */0,
-            _0: 6
-          }
-        ] : (
-          env.no_in ? undefined : [
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_IN */15 :
+          ret = env.no_in ? undefined : [
               /* In */20,
               {
                 TAG: /* Left_assoc */0,
                 _0: 6
               }
-            ]
-        );
-    } else if (match >= 80) {
-      switch (match) {
-        case /* T_BIT_OR */80 :
-            ret = [
-              /* BitOr */17,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 2
-              }
-            ];
-            break;
-        case /* T_BIT_XOR */81 :
-            ret = [
-              /* Xor */18,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 3
-              }
-            ];
-            break;
-        case /* T_BIT_AND */82 :
-            ret = [
-              /* BitAnd */19,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 4
-              }
-            ];
-            break;
-        case /* T_EQUAL */83 :
-            ret = [
-              /* Equal */0,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 5
-              }
-            ];
-            break;
-        case /* T_NOT_EQUAL */84 :
-            ret = [
-              /* NotEqual */1,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 5
-              }
-            ];
-            break;
-        case /* T_STRICT_EQUAL */85 :
-            ret = [
-              /* StrictEqual */2,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 5
-              }
-            ];
-            break;
-        case /* T_STRICT_NOT_EQUAL */86 :
-            ret = [
-              /* StrictNotEqual */3,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 5
-              }
-            ];
-            break;
-        case /* T_LESS_THAN_EQUAL */87 :
-            ret = [
-              /* LessThanEqual */5,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 6
-              }
-            ];
-            break;
-        case /* T_GREATER_THAN_EQUAL */88 :
-            ret = [
-              /* GreaterThanEqual */7,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 6
-              }
-            ];
-            break;
-        case /* T_LESS_THAN */89 :
-            ret = [
-              /* LessThan */4,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 6
-              }
-            ];
-            break;
-        case /* T_GREATER_THAN */90 :
-            ret = [
-              /* GreaterThan */6,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 6
-              }
-            ];
-            break;
-        case /* T_LSHIFT */91 :
-            ret = [
-              /* LShift */8,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 7
-              }
-            ];
-            break;
-        case /* T_RSHIFT */92 :
-            ret = [
-              /* RShift */9,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 7
-              }
-            ];
-            break;
-        case /* T_RSHIFT3 */93 :
-            ret = [
-              /* RShift3 */10,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 7
-              }
-            ];
-            break;
-        case /* T_PLUS */94 :
-            ret = [
-              /* Plus */11,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 8
-              }
-            ];
-            break;
-        case /* T_MINUS */95 :
-            ret = [
-              /* Minus */12,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 8
-              }
             ];
-            break;
-        case /* T_DIV */96 :
-            ret = [
-              /* Div */15,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 9
-              }
-            ];
-            break;
-        case /* T_MULT */97 :
-            ret = [
-              /* Mult */13,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 9
-              }
-            ];
-            break;
-        case /* T_EXP */98 :
-            ret = [
-              /* Exp */14,
-              {
-                TAG: /* Right_assoc */1,
-                _0: 10
-              }
-            ];
-            break;
-        case /* T_MOD */99 :
-            ret = [
-              /* Mod */16,
-              {
-                TAG: /* Left_assoc */0,
-                _0: 9
-              }
-            ];
-            break;
-        case /* T_NOT */100 :
-        case /* T_BIT_NOT */101 :
-        case /* T_INCR */102 :
-        case /* T_DECR */103 :
-        case /* T_ERROR */104 :
-        case /* T_EOF */105 :
-        case /* T_JSX_IDENTIFIER */106 :
-        case /* T_ANY_TYPE */107 :
-        case /* T_BOOLEAN_TYPE */108 :
-        case /* T_NUMBER_TYPE */109 :
-        case /* T_STRING_TYPE */110 :
-        case /* T_VOID_TYPE */111 :
-            ret = undefined;
-            break;
-        
-      }
-    } else {
-      ret = undefined;
+          break;
+      case /* T_INSTANCEOF */16 :
+          ret = [
+            /* Instanceof */21,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 6
+            }
+          ];
+          break;
+      case /* T_BIT_OR */80 :
+          ret = [
+            /* BitOr */17,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 2
+            }
+          ];
+          break;
+      case /* T_BIT_XOR */81 :
+          ret = [
+            /* Xor */18,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 3
+            }
+          ];
+          break;
+      case /* T_BIT_AND */82 :
+          ret = [
+            /* BitAnd */19,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 4
+            }
+          ];
+          break;
+      case /* T_EQUAL */83 :
+          ret = [
+            /* Equal */0,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 5
+            }
+          ];
+          break;
+      case /* T_NOT_EQUAL */84 :
+          ret = [
+            /* NotEqual */1,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 5
+            }
+          ];
+          break;
+      case /* T_STRICT_EQUAL */85 :
+          ret = [
+            /* StrictEqual */2,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 5
+            }
+          ];
+          break;
+      case /* T_STRICT_NOT_EQUAL */86 :
+          ret = [
+            /* StrictNotEqual */3,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 5
+            }
+          ];
+          break;
+      case /* T_LESS_THAN_EQUAL */87 :
+          ret = [
+            /* LessThanEqual */5,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 6
+            }
+          ];
+          break;
+      case /* T_GREATER_THAN_EQUAL */88 :
+          ret = [
+            /* GreaterThanEqual */7,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 6
+            }
+          ];
+          break;
+      case /* T_LESS_THAN */89 :
+          ret = [
+            /* LessThan */4,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 6
+            }
+          ];
+          break;
+      case /* T_GREATER_THAN */90 :
+          ret = [
+            /* GreaterThan */6,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 6
+            }
+          ];
+          break;
+      case /* T_LSHIFT */91 :
+          ret = [
+            /* LShift */8,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 7
+            }
+          ];
+          break;
+      case /* T_RSHIFT */92 :
+          ret = [
+            /* RShift */9,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 7
+            }
+          ];
+          break;
+      case /* T_RSHIFT3 */93 :
+          ret = [
+            /* RShift3 */10,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 7
+            }
+          ];
+          break;
+      case /* T_PLUS */94 :
+          ret = [
+            /* Plus */11,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 8
+            }
+          ];
+          break;
+      case /* T_MINUS */95 :
+          ret = [
+            /* Minus */12,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 8
+            }
+          ];
+          break;
+      case /* T_DIV */96 :
+          ret = [
+            /* Div */15,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 9
+            }
+          ];
+          break;
+      case /* T_MULT */97 :
+          ret = [
+            /* Mult */13,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 9
+            }
+          ];
+          break;
+      case /* T_EXP */98 :
+          ret = [
+            /* Exp */14,
+            {
+              TAG: /* Right_assoc */1,
+              _0: 10
+            }
+          ];
+          break;
+      case /* T_MOD */99 :
+          ret = [
+            /* Mod */16,
+            {
+              TAG: /* Left_assoc */0,
+              _0: 9
+            }
+          ];
+          break;
+      default:
+        ret = undefined;
     }
   } else {
     ret = undefined;
@@ -9769,7 +9880,7 @@ function binary(env) {
     var right_loc = btwn(start_loc, end_loc);
     if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_LESS_THAN */89) {
       var tmp = right[1];
-      if (typeof tmp !== "number" && tmp.TAG === /* JSXElement */22) {
+      if (/* tag */typeof tmp !== "number" && tmp.TAG === /* JSXElement */22) {
         error(env, /* AdjacentJSXElements */46);
       }
       
@@ -9811,7 +9922,13 @@ function binary(env) {
 
 function argument(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (match !== 11) {
+  if (/* tag */typeof match !== "number") {
+    return {
+            TAG: /* Expression */0,
+            _0: Curry._1(assignment, env)
+          };
+  }
+  if (match !== /* T_ELLIPSIS */11) {
     return {
             TAG: /* Expression */0,
             _0: Curry._1(assignment, env)
@@ -9836,14 +9953,14 @@ function arguments$p(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 4) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RPAREN */4 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var acc_0 = argument(env);
     var acc$1 = {
@@ -9880,11 +9997,11 @@ function template_parts(env, _quasis, _expressions) {
       tl: expressions
     };
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match === 2) {
+    if (/* tag */typeof match === "number" && match === /* T_RCURLY */2) {
       push_lex_mode(env, /* TEMPLATE */4);
       var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
       var match$2;
-      if (typeof match$1 === "number") {
+      if (/* tag */typeof match$1 === "number") {
         throw {
               RE_EXN_ID: "Assert_failure",
               _1: [
@@ -10011,54 +10128,40 @@ function elements(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 105) {
-        return List.rev(acc);
-      }
-      if (match < 12) {
-        switch (match) {
-          case /* T_RBRACKET */6 :
-              return List.rev(acc);
-          case /* T_COMMA */8 :
-              token$4(env, /* T_COMMA */8);
-              _acc = {
-                hd: undefined,
-                tl: acc
-              };
-              continue ;
-          case /* T_IDENTIFIER */0 :
-          case /* T_LCURLY */1 :
-          case /* T_RCURLY */2 :
-          case /* T_LPAREN */3 :
-          case /* T_RPAREN */4 :
-          case /* T_LBRACKET */5 :
-          case /* T_SEMICOLON */7 :
-          case /* T_PERIOD */9 :
-          case /* T_ARROW */10 :
-              break;
-          case /* T_ELLIPSIS */11 :
-              var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-              token$4(env, /* T_ELLIPSIS */11);
-              var argument = Curry._1(assignment, env);
-              var loc = btwn(start_loc, argument[0]);
-              var elem = {
-                TAG: /* Spread */1,
-                _0: [
-                  loc,
-                  {
-                    argument: argument
-                  }
-                ]
-              };
-              _acc = {
-                hd: elem,
-                tl: acc
-              };
-              continue ;
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_COMMA */8 :
+            token$4(env, /* T_COMMA */8);
+            _acc = {
+              hd: undefined,
+              tl: acc
+            };
+            continue ;
+        case /* T_ELLIPSIS */11 :
+            var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_ELLIPSIS */11);
+            var argument = Curry._1(assignment, env);
+            var loc = btwn(start_loc, argument[0]);
+            var elem = {
+              TAG: /* Spread */1,
+              _0: [
+                loc,
+                {
+                  argument: argument
+                }
+              ]
+            };
+            _acc = {
+              hd: elem,
+              tl: acc
+            };
+            continue ;
+        case /* T_RBRACKET */6 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
           
-        }
       }
-      
     }
     var elem$1 = {
       TAG: /* Expression */0,
@@ -10090,28 +10193,24 @@ function array_initializer(env) {
 }
 
 function error_callback$1(param, param$1) {
-  if (typeof param$1 === "number") {
-    if (param$1 > 44 || param$1 < 28) {
-      if (param$1 === 47) {
-        return ;
-      }
-      throw {
-            RE_EXN_ID: Parser_env_Try.Rollback,
-            Error: new Error()
-          };
-    }
-    if (param$1 > 43 || param$1 < 29) {
-      return ;
+  if (/* tag */typeof param$1 === "number") {
+    switch (param$1) {
+      case /* StrictParamName */28 :
+      case /* NewlineBeforeArrow */44 :
+      case /* ParameterAfterRestParameter */47 :
+          return ;
+      default:
+        throw {
+              RE_EXN_ID: Parser_env_Try.Rollback,
+              Error: new Error()
+            };
     }
+  } else {
     throw {
           RE_EXN_ID: Parser_env_Try.Rollback,
           Error: new Error()
         };
   }
-  throw {
-        RE_EXN_ID: Parser_env_Try.Rollback,
-        Error: new Error()
-      };
 }
 
 function try_arrow_function(env) {
@@ -10163,7 +10262,7 @@ function try_arrow_function(env) {
           var generator = false;
           var env = with_in_function(true, param);
           var match = Curry._2(Parser_env_Peek.token, undefined, env);
-          if (match === 1) {
+          if (/* tag */typeof match === "number" && match === /* T_LCURLY */1) {
             var match$1 = function_body(env, async, generator);
             return [
                     match$1[1],
@@ -10212,7 +10311,10 @@ function decorator_list_helper(env, _decorators) {
   while(true) {
     var decorators = _decorators;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 12) {
+    if (/* tag */typeof match !== "number") {
+      return decorators;
+    }
+    if (match !== /* T_AT */12) {
       return decorators;
     }
     token$3(env);
@@ -10234,7 +10336,7 @@ function decorator_list(env) {
 
 function key(env) {
   var number_type = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof number_type === "number") {
+  if (/* tag */typeof number_type === "number") {
     if (number_type === /* T_LBRACKET */5) {
       var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
       token$4(env, /* T_LBRACKET */5);
@@ -10326,7 +10428,17 @@ function key(env) {
 function _method(env, kind) {
   var generator$1 = generator(env, false);
   var match = key(env);
-  var typeParameters = kind !== 0 ? undefined : Curry._1(type_parameter_declaration$1, env);
+  var typeParameters;
+  switch (kind) {
+    case /* Init */0 :
+        typeParameters = Curry._1(type_parameter_declaration$1, env);
+        break;
+    case /* Get */1 :
+    case /* Set */2 :
+        typeParameters = undefined;
+        break;
+    
+  }
   token$4(env, /* T_LPAREN */3);
   var params;
   switch (kind) {
@@ -10425,23 +10537,43 @@ function property$1(env) {
           switch (key$1._0[1].name) {
             case "get" :
                 var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
-                tmp = typeof match$2 === "number" ? (
-                    match$2 > 77 || match$2 < 3 ? (
-                        match$2 !== 89 ? get(env, start_loc) : init(env, start_loc, key$1, false, false)
-                      ) : (
-                        match$2 > 76 || match$2 < 4 ? init(env, start_loc, key$1, false, false) : get(env, start_loc)
-                      )
-                  ) : get(env, start_loc);
+                var exit$1 = 0;
+                if (/* tag */typeof match$2 === "number") {
+                  switch (match$2) {
+                    case /* T_LPAREN */3 :
+                    case /* T_COLON */77 :
+                    case /* T_LESS_THAN */89 :
+                        exit$1 = 2;
+                        break;
+                    default:
+                      tmp = get(env, start_loc);
+                  }
+                } else {
+                  tmp = get(env, start_loc);
+                }
+                if (exit$1 === 2) {
+                  tmp = init(env, start_loc, key$1, false, false);
+                }
                 break;
             case "set" :
                 var match$3 = Curry._2(Parser_env_Peek.token, undefined, env);
-                tmp = typeof match$3 === "number" ? (
-                    match$3 > 77 || match$3 < 3 ? (
-                        match$3 !== 89 ? set(env, start_loc) : init(env, start_loc, key$1, false, false)
-                      ) : (
-                        match$3 > 76 || match$3 < 4 ? init(env, start_loc, key$1, false, false) : set(env, start_loc)
-                      )
-                  ) : set(env, start_loc);
+                var exit$2 = 0;
+                if (/* tag */typeof match$3 === "number") {
+                  switch (match$3) {
+                    case /* T_LPAREN */3 :
+                    case /* T_COLON */77 :
+                    case /* T_LESS_THAN */89 :
+                        exit$2 = 2;
+                        break;
+                    default:
+                      tmp = set(env, start_loc);
+                  }
+                } else {
+                  tmp = set(env, start_loc);
+                }
+                if (exit$2 === 2) {
+                  tmp = init(env, start_loc, key$1, false, false);
+                }
                 break;
             default:
               exit = 1;
@@ -10515,32 +10647,18 @@ function init(env, start_loc, key, async, generator) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var match$1;
   var exit = 0;
-  if (typeof match === "number") {
-    if (match !== 89) {
-      if (match >= 9) {
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_RCURLY */2 :
+      case /* T_COMMA */8 :
+          exit = 2;
+          break;
+      case /* T_LPAREN */3 :
+      case /* T_LESS_THAN */89 :
+          exit = 3;
+          break;
+      default:
         exit = 1;
-      } else {
-        switch (match) {
-          case /* T_LPAREN */3 :
-              exit = 3;
-              break;
-          case /* T_IDENTIFIER */0 :
-          case /* T_LCURLY */1 :
-          case /* T_RPAREN */4 :
-          case /* T_LBRACKET */5 :
-          case /* T_RBRACKET */6 :
-          case /* T_SEMICOLON */7 :
-              exit = 1;
-              break;
-          case /* T_RCURLY */2 :
-          case /* T_COMMA */8 :
-              exit = 2;
-              break;
-          
-        }
-      }
-    } else {
-      exit = 3;
     }
   } else {
     exit = 1;
@@ -10672,7 +10790,7 @@ function check_property(env, prop_map, prop) {
     switch (match$1.TAG | 0) {
       case /* Literal */0 :
           var s = match$1._0[1].value;
-          if (typeof s === "number") {
+          if (/* tag */typeof s === "number") {
             key = "null";
           } else {
             switch (s.TAG | 0) {
@@ -10784,14 +10902,14 @@ function properties$1(env, _param) {
     var param = _param;
     var acc = param[1];
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 2) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var prop = property$1(env);
     var prop_map = check_property(env, param[0], prop);
@@ -10845,7 +10963,10 @@ function class_implements(env, _acc) {
       tl: acc
     };
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 8) {
+    if (/* tag */typeof match !== "number") {
+      return List.rev(acc$1);
+    }
+    if (match !== /* T_COMMA */8) {
       return List.rev(acc$1);
     }
     token$4(env, /* T_COMMA */8);
@@ -10854,19 +10975,55 @@ function class_implements(env, _acc) {
   };
 }
 
-function init$1(env, start_loc, decorators, key, async, generator, $$static) {
-  var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  var exit = 0;
-  if (typeof match === "number") {
-    if (match > 77 || match < 75) {
-      if (match === 7) {
-        exit = 2;
-      }
-      
-    } else if (match !== 76) {
-      exit = 2;
+function get$1(env, start_loc, decorators, $$static) {
+  var match = _method(env, /* Get */1);
+  var value = match[1];
+  return {
+          TAG: /* Method */0,
+          _0: [
+            btwn(start_loc, value[0]),
+            {
+              kind: /* Get */2,
+              key: match[0],
+              value: value,
+              static: $$static,
+              decorators: decorators
+            }
+          ]
+        };
+}
+
+function set$1(env, start_loc, decorators, $$static) {
+  var match = _method(env, /* Set */2);
+  var value = match[1];
+  return {
+          TAG: /* Method */0,
+          _0: [
+            btwn(start_loc, value[0]),
+            {
+              kind: /* Set */3,
+              key: match[0],
+              value: value,
+              static: $$static,
+              decorators: decorators
+            }
+          ]
+        };
+}
+
+function init$1(env, start_loc, decorators, key, async, generator, $$static) {
+  var match = Curry._2(Parser_env_Peek.token, undefined, env);
+  var exit = 0;
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_SEMICOLON */7 :
+      case /* T_ASSIGN */75 :
+      case /* T_COLON */77 :
+          exit = 2;
+          break;
+      default:
+        
     }
-    
   }
   if (exit === 2 && !async && !generator) {
     var typeAnnotation = wrap(annotation_opt, env);
@@ -10932,7 +11089,7 @@ function init$1(env, start_loc, decorators, key, async, generator, $$static) {
   switch (key.TAG | 0) {
     case /* Literal */0 :
         var match$4 = key._0[1].value;
-        kind = typeof match$4 === "number" || !(match$4.TAG === /* String */0 && match$4._0 === "constructor") ? /* Method */1 : /* Constructor */0;
+        kind = /* tag */typeof match$4 === "number" || !(match$4.TAG === /* String */0 && match$4._0 === "constructor") ? /* Method */1 : /* Constructor */0;
         break;
     case /* Identifier */1 :
         kind = key._0[1].name === "constructor" ? /* Constructor */0 : /* Method */1;
@@ -10972,73 +11129,43 @@ function class_element(env) {
             case "get" :
                 var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
                 var exit = 0;
-                exit = typeof match$1 === "number" ? (
-                    match$1 >= 75 ? (
-                        match$1 >= 78 ? (
-                            match$1 !== 89 ? 2 : 3
-                          ) : (
-                            match$1 !== 76 ? 3 : 2
-                          )
-                      ) : (
-                        match$1 !== 3 && match$1 !== 7 ? 2 : 3
-                      )
-                  ) : 2;
-                switch (exit) {
-                  case 2 :
-                      var match$2 = _method(env, /* Get */1);
-                      var value = match$2[1];
-                      return {
-                              TAG: /* Method */0,
-                              _0: [
-                                btwn(start_loc, value[0]),
-                                {
-                                  kind: /* Get */2,
-                                  key: match$2[0],
-                                  value: value,
-                                  static: $$static,
-                                  decorators: decorators
-                                }
-                              ]
-                            };
-                  case 3 :
-                      return init$1(env, start_loc, decorators, key$1, async, generator$1, $$static);
-                  
+                if (/* tag */typeof match$1 !== "number") {
+                  return get$1(env, start_loc, decorators, $$static);
+                }
+                switch (match$1) {
+                  case /* T_LPAREN */3 :
+                  case /* T_SEMICOLON */7 :
+                  case /* T_ASSIGN */75 :
+                  case /* T_COLON */77 :
+                  case /* T_LESS_THAN */89 :
+                      exit = 2;
+                      break;
+                  default:
+                    return get$1(env, start_loc, decorators, $$static);
+                }
+                if (exit === 2) {
+                  return init$1(env, start_loc, decorators, key$1, async, generator$1, $$static);
                 }
                 break;
             case "set" :
-                var match$3 = Curry._2(Parser_env_Peek.token, undefined, env);
+                var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
                 var exit$1 = 0;
-                exit$1 = typeof match$3 === "number" ? (
-                    match$3 >= 75 ? (
-                        match$3 >= 78 ? (
-                            match$3 !== 89 ? 2 : 3
-                          ) : (
-                            match$3 !== 76 ? 3 : 2
-                          )
-                      ) : (
-                        match$3 !== 3 && match$3 !== 7 ? 2 : 3
-                      )
-                  ) : 2;
-                switch (exit$1) {
-                  case 2 :
-                      var match$4 = _method(env, /* Set */2);
-                      var value$1 = match$4[1];
-                      return {
-                              TAG: /* Method */0,
-                              _0: [
-                                btwn(start_loc, value$1[0]),
-                                {
-                                  kind: /* Set */3,
-                                  key: match$4[0],
-                                  value: value$1,
-                                  static: $$static,
-                                  decorators: decorators
-                                }
-                              ]
-                            };
-                  case 3 :
-                      return init$1(env, start_loc, decorators, key$1, async, generator$1, $$static);
-                  
+                if (/* tag */typeof match$2 !== "number") {
+                  return set$1(env, start_loc, decorators, $$static);
+                }
+                switch (match$2) {
+                  case /* T_LPAREN */3 :
+                  case /* T_SEMICOLON */7 :
+                  case /* T_ASSIGN */75 :
+                  case /* T_COLON */77 :
+                  case /* T_LESS_THAN */89 :
+                      exit$1 = 2;
+                      break;
+                  default:
+                    return set$1(env, start_loc, decorators, $$static);
+                }
+                if (exit$1 === 2) {
+                  return init$1(env, start_loc, decorators, key$1, async, generator$1, $$static);
                 }
                 break;
             default:
@@ -11058,23 +11185,28 @@ function elements$1(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match > 104 || match < 3) {
-        if (!(match > 105 || match < 2)) {
-          return List.rev(acc);
-        }
-        
-      } else if (match === 7) {
-        token$4(env, /* T_SEMICOLON */7);
-        continue ;
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_SEMICOLON */7 :
+            token$4(env, /* T_SEMICOLON */7);
+            continue ;
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          _acc = {
+            hd: Curry._1(class_element, env),
+            tl: acc
+          };
+          continue ;
       }
-      
+    } else {
+      _acc = {
+        hd: Curry._1(class_element, env),
+        tl: acc
+      };
+      continue ;
     }
-    _acc = {
-      hd: Curry._1(class_element, env),
-      tl: acc
-    };
-    continue ;
   };
 }
 
@@ -11155,23 +11287,18 @@ function class_expression(env) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
   var match$1;
   var exit = 0;
-  if (typeof match === "number") {
-    if (match > 39 || match < 1) {
-      if (match !== 89) {
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_LCURLY */1 :
+      case /* T_EXTENDS */39 :
+      case /* T_LESS_THAN */89 :
+          match$1 = [
+            undefined,
+            undefined
+          ];
+          break;
+      default:
         exit = 1;
-      } else {
-        match$1 = [
-          undefined,
-          undefined
-        ];
-      }
-    } else if (match > 38 || match < 2) {
-      match$1 = [
-        undefined,
-        undefined
-      ];
-    } else {
-      exit = 1;
     }
   } else {
     exit = 1;
@@ -11261,20 +11388,17 @@ function export_specifiers_and_errs(env, _specifiers, _errs) {
     var errs = _errs;
     var specifiers = _specifiers;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 2) {
-        return [
-                List.rev(specifiers),
-                List.rev(errs)
-              ];
-      }
-      if (match === 105) {
-        return [
-                List.rev(specifiers),
-                List.rev(errs)
-              ];
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return [
+                    List.rev(specifiers),
+                    List.rev(errs)
+                  ];
+        default:
+          
       }
-      
     }
     var match$1 = Curry._1(Parse.identifier_or_reserved_keyword, env);
     var id = match$1[0];
@@ -11348,7 +11472,7 @@ function declare_var(env, start_loc) {
 function export_source(env) {
   contextual(env, "from");
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number" && match.TAG === /* T_STRING */1) {
+  if (/* tag */typeof match !== "number" && match.TAG === /* T_STRING */1) {
     var match$1 = match._0;
     var octal = match$1[3];
     var raw = match$1[2];
@@ -11428,162 +11552,135 @@ function declare(in_moduleOpt, env) {
   }
   var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var match = Curry._2(Parser_env_Peek.token, 1, env);
-  if (typeof match === "number") {
-    if (match >= 22) {
-      if (match >= 38) {
-        if (match < 62) {
-          switch (match) {
-            case /* T_CLASS */38 :
-                token$4(env, /* T_DECLARE */58);
-                var match$1 = Curry._2(declare_class, env, start_loc);
-                return [
-                        match$1[0],
-                        {
-                          TAG: /* DeclareClass */24,
-                          _0: match$1[1]
-                        }
-                      ];
-            case /* T_EXPORT */47 :
-                if (in_module) {
-                  return declare_export_declaration(in_module, env);
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_IDENTIFIER */0 :
+          if (Curry._2(Parser_env_Peek.value, 1, env) === "module") {
+            token$4(env, /* T_DECLARE */58);
+            contextual(env, "module");
+            if (in_module || Curry._2(Parser_env_Peek.token, undefined, env) === /* T_PERIOD */9) {
+              token$4(env, /* T_PERIOD */9);
+              contextual(env, "exports");
+              var type_annot = wrap(annotation, env);
+              var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+              var end_loc = loc !== undefined ? loc : type_annot[0];
+              semicolon(env);
+              var loc$1 = btwn(start_loc, end_loc);
+              return [
+                      loc$1,
+                      {
+                        TAG: /* DeclareModuleExports */26,
+                        _0: type_annot
+                      }
+                    ];
+            } else {
+              var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
+              var id;
+              if (/* tag */typeof match$1 === "number" || match$1.TAG !== /* T_STRING */1) {
+                id = {
+                  TAG: /* Identifier */0,
+                  _0: Curry._2(Parse.identifier, undefined, env)
+                };
+              } else {
+                var match$2 = match$1._0;
+                var octal = match$2[3];
+                var raw = match$2[2];
+                var value = match$2[1];
+                var loc$2 = match$2[0];
+                if (octal) {
+                  strict_error(env, /* StrictOctalLiteral */31);
                 }
-                break;
-            case /* T_INTERFACE */51 :
-                token$4(env, /* T_DECLARE */58);
-                return $$interface(env);
-            case /* T_TYPE */59 :
-                token$4(env, /* T_DECLARE */58);
-                return type_alias(env);
-            case /* T_EXTENDS */39 :
-            case /* T_STATIC */40 :
-            case /* T_ELSE */41 :
-            case /* T_NEW */42 :
-            case /* T_DELETE */43 :
-            case /* T_TYPEOF */44 :
-            case /* T_VOID */45 :
-            case /* T_ENUM */46 :
-            case /* T_IMPORT */48 :
-            case /* T_SUPER */49 :
-            case /* T_IMPLEMENTS */50 :
-            case /* T_PACKAGE */52 :
-            case /* T_PRIVATE */53 :
-            case /* T_PROTECTED */54 :
-            case /* T_PUBLIC */55 :
-            case /* T_YIELD */56 :
-            case /* T_DEBUGGER */57 :
-            case /* T_DECLARE */58 :
-            case /* T_OF */60 :
-                break;
-            case /* T_ASYNC */61 :
-                token$4(env, /* T_DECLARE */58);
-                error(env, /* DeclareAsync */49);
-                token$4(env, /* T_ASYNC */61);
-                return declare_function_statement(env, start_loc);
-            
-          }
-        }
-        
-      } else if (match < 23) {
-        token$4(env, /* T_DECLARE */58);
-        return declare_var_statement(env, start_loc);
-      }
-      
-    } else if (match !== 13) {
-      if (match === 0 && Curry._2(Parser_env_Peek.value, 1, env) === "module") {
-        token$4(env, /* T_DECLARE */58);
-        contextual(env, "module");
-        if (in_module || Curry._2(Parser_env_Peek.token, undefined, env) === /* T_PERIOD */9) {
-          token$4(env, /* T_PERIOD */9);
-          contextual(env, "exports");
-          var type_annot = wrap(annotation, env);
-          var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-          var end_loc = loc !== undefined ? loc : type_annot[0];
-          semicolon(env);
-          var loc$1 = btwn(start_loc, end_loc);
-          return [
-                  loc$1,
-                  {
-                    TAG: /* DeclareModuleExports */26,
-                    _0: type_annot
-                  }
-                ];
-        } else {
-          var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
-          var id;
-          if (typeof match$2 === "number" || match$2.TAG !== /* T_STRING */1) {
-            id = {
-              TAG: /* Identifier */0,
-              _0: Curry._2(Parse.identifier, undefined, env)
-            };
-          } else {
-            var match$3 = match$2._0;
-            var octal = match$3[3];
-            var raw = match$3[2];
-            var value = match$3[1];
-            var loc$2 = match$3[0];
-            if (octal) {
-              strict_error(env, /* StrictOctalLiteral */31);
-            }
-            token$4(env, {
-                  TAG: /* T_STRING */1,
+                token$4(env, {
+                      TAG: /* T_STRING */1,
+                      _0: [
+                        loc$2,
+                        value,
+                        raw,
+                        octal
+                      ]
+                    });
+                var value$1 = {
+                  TAG: /* String */0,
+                  _0: value
+                };
+                id = {
+                  TAG: /* Literal */1,
                   _0: [
                     loc$2,
-                    value,
-                    raw,
-                    octal
+                    {
+                      value: value$1,
+                      raw: raw
+                    }
                   ]
-                });
-            var value$1 = {
-              TAG: /* String */0,
-              _0: value
-            };
-            id = {
-              TAG: /* Literal */1,
-              _0: [
-                loc$2,
-                {
-                  value: value$1,
-                  raw: raw
-                }
-              ]
-            };
+                };
+              }
+              var body_start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+              token$4(env, /* T_LCURLY */1);
+              var match$3 = module_items(env, undefined, /* [] */0);
+              var module_kind = match$3[0];
+              token$4(env, /* T_RCURLY */2);
+              var body_end_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+              var body_loc = btwn(body_start_loc, body_end_loc);
+              var body_1 = {
+                body: match$3[1]
+              };
+              var body = [
+                body_loc,
+                body_1
+              ];
+              var loc$3 = btwn(start_loc, body_loc);
+              var kind = module_kind !== undefined ? module_kind : ({
+                    TAG: /* CommonJS */0,
+                    _0: loc$3
+                  });
+              return [
+                      loc$3,
+                      {
+                        TAG: /* DeclareModule */25,
+                        _0: {
+                          id: id,
+                          body: body,
+                          kind: kind
+                        }
+                      }
+                    ];
+            }
           }
-          var body_start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-          token$4(env, /* T_LCURLY */1);
-          var match$4 = module_items(env, undefined, /* [] */0);
-          var module_kind = match$4[0];
-          token$4(env, /* T_RCURLY */2);
-          var body_end_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-          var body_loc = btwn(body_start_loc, body_end_loc);
-          var body_1 = {
-            body: match$4[1]
-          };
-          var body = [
-            body_loc,
-            body_1
-          ];
-          var loc$3 = btwn(start_loc, body_loc);
-          var kind = module_kind !== undefined ? module_kind : ({
-                TAG: /* CommonJS */0,
-                _0: loc$3
-              });
+          break;
+      case /* T_FUNCTION */13 :
+          token$4(env, /* T_DECLARE */58);
+          return declare_function_statement(env, start_loc);
+      case /* T_VAR */22 :
+          token$4(env, /* T_DECLARE */58);
+          return declare_var_statement(env, start_loc);
+      case /* T_CLASS */38 :
+          token$4(env, /* T_DECLARE */58);
+          var match$4 = Curry._2(declare_class, env, start_loc);
           return [
-                  loc$3,
+                  match$4[0],
                   {
-                    TAG: /* DeclareModule */25,
-                    _0: {
-                      id: id,
-                      body: body,
-                      kind: kind
-                    }
+                    TAG: /* DeclareClass */24,
+                    _0: match$4[1]
                   }
                 ];
-        }
-      }
-      
-    } else {
-      token$4(env, /* T_DECLARE */58);
-      return declare_function_statement(env, start_loc);
+      case /* T_EXPORT */47 :
+          if (in_module) {
+            return declare_export_declaration(in_module, env);
+          }
+          break;
+      case /* T_INTERFACE */51 :
+          token$4(env, /* T_DECLARE */58);
+          return $$interface(env);
+      case /* T_TYPE */59 :
+          token$4(env, /* T_DECLARE */58);
+          return type_alias(env);
+      case /* T_ASYNC */61 :
+          token$4(env, /* T_DECLARE */58);
+          error(env, /* DeclareAsync */49);
+          token$4(env, /* T_ASYNC */61);
+          return declare_function_statement(env, start_loc);
+      default:
+        
     }
   }
   if (in_module) {
@@ -11671,186 +11768,154 @@ function declare_export_declaration(allow_export_typeOpt, env) {
   token$4(env$1, /* T_EXPORT */47);
   var match = Curry._2(Parser_env_Peek.token, undefined, env$1);
   var exit = 0;
-  if (typeof match === "number") {
-    if (match >= 52) {
-      if (match !== 59) {
-        if (match !== 97) {
-          exit = 1;
-        } else {
-          var loc = Curry._2(Parser_env_Peek.loc, undefined, env$1);
-          token$4(env$1, /* T_MULT */97);
-          var parse_export_star_as = env$1.parse_options.esproposal_export_star_as;
-          var local_name = Curry._2(Parser_env_Peek.value, undefined, env$1) === "as" ? (contextual(env$1, "as"), parse_export_star_as ? Curry._2(Parse.identifier, undefined, env$1) : (error(env$1, /* UnexpectedTypeDeclaration */7), undefined)) : undefined;
-          var specifiers = {
-            TAG: /* ExportBatchSpecifier */1,
-            _0: loc,
-            _1: local_name
-          };
-          var source = export_source(env$1);
-          var loc$1 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
-          var end_loc = loc$1 !== undefined ? loc$1 : source[0];
-          var source$1 = source;
-          semicolon(env$1);
-          return [
-                  btwn(start_loc, end_loc),
-                  {
-                    TAG: /* DeclareExportDeclaration */27,
-                    _0: {
-                      default: false,
-                      declaration: undefined,
-                      specifiers: specifiers,
-                      source: source$1
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_DEFAULT */34 :
+          token$4(env$1, /* T_DEFAULT */34);
+          var match$1 = Curry._2(Parser_env_Peek.token, undefined, env$1);
+          var match$2;
+          var exit$1 = 0;
+          if (/* tag */typeof match$1 === "number") {
+            switch (match$1) {
+              case /* T_FUNCTION */13 :
+                  var fn = declare_function(env$1, start_loc);
+                  match$2 = [
+                    fn[0],
+                    {
+                      TAG: /* Function */1,
+                      _0: fn
                     }
-                  }
-                ];
-        }
-      } else {
-        if (allow_export_type) {
-          var match$1 = type_alias_helper(env$1);
-          var alias_loc = match$1[0];
-          var loc$2 = btwn(start_loc, alias_loc);
-          return [
-                  loc$2,
-                  {
-                    TAG: /* DeclareExportDeclaration */27,
-                    _0: {
-                      default: false,
-                      declaration: {
-                        TAG: /* NamedType */4,
-                        _0: [
-                          alias_loc,
-                          match$1[1]
-                        ]
-                      },
-                      specifiers: undefined,
-                      source: undefined
+                  ];
+                  break;
+              case /* T_CLASS */38 :
+                  var _class = Curry._2(declare_class, env$1, start_loc);
+                  match$2 = [
+                    _class[0],
+                    {
+                      TAG: /* Class */2,
+                      _0: _class
                     }
-                  }
-                ];
-        }
-        exit = 1;
-      }
-    } else if (match >= 39) {
-      if (match >= 51) {
-        if (allow_export_type) {
-          var match$2 = Curry._1(interface_helper, env$1);
-          var iface_loc = match$2[0];
-          var loc$3 = btwn(start_loc, iface_loc);
+                  ];
+                  break;
+              default:
+                exit$1 = 3;
+            }
+          } else {
+            exit$1 = 3;
+          }
+          if (exit$1 === 3) {
+            var _type$1 = wrap(_type, env$1);
+            var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
+            var end_loc = loc !== undefined ? loc : _type$1[0];
+            semicolon(env$1);
+            match$2 = [
+              end_loc,
+              {
+                TAG: /* DefaultType */3,
+                _0: _type$1
+              }
+            ];
+          }
           return [
-                  loc$3,
+                  btwn(start_loc, match$2[0]),
                   {
                     TAG: /* DeclareExportDeclaration */27,
                     _0: {
-                      default: false,
-                      declaration: {
-                        TAG: /* Interface */5,
-                        _0: [
-                          iface_loc,
-                          match$2[1]
-                        ]
-                      },
+                      default: true,
+                      declaration: match$2[1],
                       specifiers: undefined,
                       source: undefined
                     }
                   }
                 ];
-        }
-        exit = 1;
-      } else {
-        exit = 1;
-      }
-    } else if (match >= 13) {
-      switch (match) {
-        case /* T_DEFAULT */34 :
-            token$4(env$1, /* T_DEFAULT */34);
-            var match$3 = Curry._2(Parser_env_Peek.token, undefined, env$1);
-            var match$4;
-            var exit$1 = 0;
-            if (typeof match$3 === "number") {
-              if (match$3 !== 13) {
-                if (match$3 !== 38) {
-                  exit$1 = 3;
-                } else {
-                  var _class = Curry._2(declare_class, env$1, start_loc);
-                  match$4 = [
-                    _class[0],
+      case /* T_FUNCTION */13 :
+      case /* T_VAR */22 :
+      case /* T_CONST */25 :
+      case /* T_LET */26 :
+      case /* T_CLASS */38 :
+          exit = 2;
+          break;
+      case /* T_INTERFACE */51 :
+          if (allow_export_type) {
+            var match$3 = Curry._1(interface_helper, env$1);
+            var iface_loc = match$3[0];
+            var loc$1 = btwn(start_loc, iface_loc);
+            return [
+                    loc$1,
                     {
-                      TAG: /* Class */2,
-                      _0: _class
+                      TAG: /* DeclareExportDeclaration */27,
+                      _0: {
+                        default: false,
+                        declaration: {
+                          TAG: /* Interface */5,
+                          _0: [
+                            iface_loc,
+                            match$3[1]
+                          ]
+                        },
+                        specifiers: undefined,
+                        source: undefined
+                      }
                     }
                   ];
-                }
-              } else {
-                var fn = declare_function(env$1, start_loc);
-                match$4 = [
-                  fn[0],
-                  {
-                    TAG: /* Function */1,
-                    _0: fn
-                  }
-                ];
-              }
-            } else {
-              exit$1 = 3;
-            }
-            if (exit$1 === 3) {
-              var _type$1 = wrap(_type, env$1);
-              var loc$4 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
-              var end_loc$1 = loc$4 !== undefined ? loc$4 : _type$1[0];
-              semicolon(env$1);
-              match$4 = [
-                end_loc$1,
-                {
-                  TAG: /* DefaultType */3,
-                  _0: _type$1
-                }
-              ];
-            }
+          }
+          exit = 1;
+          break;
+      case /* T_TYPE */59 :
+          if (allow_export_type) {
+            var match$4 = type_alias_helper(env$1);
+            var alias_loc = match$4[0];
+            var loc$2 = btwn(start_loc, alias_loc);
             return [
-                    btwn(start_loc, match$4[0]),
+                    loc$2,
                     {
                       TAG: /* DeclareExportDeclaration */27,
                       _0: {
-                        default: true,
-                        declaration: match$4[1],
+                        default: false,
+                        declaration: {
+                          TAG: /* NamedType */4,
+                          _0: [
+                            alias_loc,
+                            match$4[1]
+                          ]
+                        },
                         specifiers: undefined,
                         source: undefined
                       }
                     }
                   ];
-        case /* T_IF */14 :
-        case /* T_IN */15 :
-        case /* T_INSTANCEOF */16 :
-        case /* T_RETURN */17 :
-        case /* T_SWITCH */18 :
-        case /* T_THIS */19 :
-        case /* T_THROW */20 :
-        case /* T_TRY */21 :
-        case /* T_WHILE */23 :
-        case /* T_WITH */24 :
-        case /* T_NULL */27 :
-        case /* T_FALSE */28 :
-        case /* T_TRUE */29 :
-        case /* T_BREAK */30 :
-        case /* T_CASE */31 :
-        case /* T_CATCH */32 :
-        case /* T_CONTINUE */33 :
-        case /* T_DO */35 :
-        case /* T_FINALLY */36 :
-        case /* T_FOR */37 :
-            exit = 1;
-            break;
-        case /* T_FUNCTION */13 :
-        case /* T_VAR */22 :
-        case /* T_CONST */25 :
-        case /* T_LET */26 :
-        case /* T_CLASS */38 :
-            exit = 2;
-            break;
-        
-      }
-    } else {
-      exit = 1;
+          }
+          exit = 1;
+          break;
+      case /* T_MULT */97 :
+          var loc$3 = Curry._2(Parser_env_Peek.loc, undefined, env$1);
+          token$4(env$1, /* T_MULT */97);
+          var parse_export_star_as = env$1.parse_options.esproposal_export_star_as;
+          var local_name = Curry._2(Parser_env_Peek.value, undefined, env$1) === "as" ? (contextual(env$1, "as"), parse_export_star_as ? Curry._2(Parse.identifier, undefined, env$1) : (error(env$1, /* UnexpectedTypeDeclaration */7), undefined)) : undefined;
+          var specifiers = {
+            TAG: /* ExportBatchSpecifier */1,
+            _0: loc$3,
+            _1: local_name
+          };
+          var source = export_source(env$1);
+          var loc$4 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
+          var end_loc$1 = loc$4 !== undefined ? loc$4 : source[0];
+          var source$1 = source;
+          semicolon(env$1);
+          return [
+                  btwn(start_loc, end_loc$1),
+                  {
+                    TAG: /* DeclareExportDeclaration */27,
+                    _0: {
+                      default: false,
+                      declaration: undefined,
+                      specifiers: specifiers,
+                      source: source$1
+                    }
+                  }
+                ];
+      default:
+        exit = 1;
     }
   } else {
     exit = 1;
@@ -11858,15 +11923,16 @@ function declare_export_declaration(allow_export_typeOpt, env) {
   switch (exit) {
     case 1 :
         var match$5 = Curry._2(Parser_env_Peek.token, undefined, env$1);
-        if (typeof match$5 === "number") {
-          if (match$5 !== 51) {
-            if (match$5 !== 59) {
+        if (/* tag */typeof match$5 === "number") {
+          switch (match$5) {
+            case /* T_INTERFACE */51 :
+                error(env$1, /* DeclareExportInterface */53);
+                break;
+            case /* T_TYPE */59 :
+                error(env$1, /* DeclareExportType */52);
+                break;
+            default:
               
-            } else {
-              error(env$1, /* DeclareExportType */52);
-            }
-          } else {
-            error(env$1, /* DeclareExportInterface */53);
           }
         }
         token$4(env$1, /* T_LCURLY */1);
@@ -11901,12 +11967,24 @@ function declare_export_declaration(allow_export_typeOpt, env) {
         var token$5 = Curry._2(Parser_env_Peek.token, undefined, env$1);
         var match$7;
         var exit$2 = 0;
-        if (typeof token$5 === "number") {
-          if (token$5 >= 23) {
-            if (token$5 >= 27) {
-              if (token$5 !== 38) {
+        if (/* tag */typeof token$5 === "number") {
+          switch (token$5) {
+            case /* T_FUNCTION */13 :
+                var fn$1 = declare_function(env$1, start_loc);
+                match$7 = [
+                  fn$1[0],
+                  {
+                    TAG: /* Function */1,
+                    _0: fn$1
+                  }
+                ];
+                break;
+            case /* T_VAR */22 :
+            case /* T_CONST */25 :
+            case /* T_LET */26 :
                 exit$2 = 3;
-              } else {
+                break;
+            case /* T_CLASS */38 :
                 var _class$1 = Curry._2(declare_class, env$1, start_loc);
                 match$7 = [
                   _class$1[0],
@@ -11915,27 +11993,8 @@ function declare_export_declaration(allow_export_typeOpt, env) {
                     _0: _class$1
                   }
                 ];
-              }
-            } else {
-              exit$2 = token$5 >= 25 ? 4 : 3;
-            }
-          } else if (token$5 !== 13) {
-            exit$2 = token$5 >= 22 ? 4 : 3;
-          } else {
-            var fn$1 = declare_function(env$1, start_loc);
-            match$7 = [
-              fn$1[0],
-              {
-                TAG: /* Function */1,
-                _0: fn$1
-              }
-            ];
-          }
-        } else {
-          exit$2 = 3;
-        }
-        switch (exit$2) {
-          case 3 :
+                break;
+            default:
               throw {
                     RE_EXN_ID: "Assert_failure",
                     _1: [
@@ -11945,28 +12004,39 @@ function declare_export_declaration(allow_export_typeOpt, env) {
                     ],
                     Error: new Error()
                   };
-          case 4 :
-              if (typeof token$5 === "number") {
-                if (token$5 !== 25) {
-                  if (token$5 !== 26) {
-                    
-                  } else {
-                    error(env$1, /* DeclareExportLet */50);
-                  }
-                } else {
+          }
+        } else {
+          throw {
+                RE_EXN_ID: "Assert_failure",
+                _1: [
+                  "parser_flow.ml",
+                  3480,
+                  17
+                ],
+                Error: new Error()
+              };
+        }
+        if (exit$2 === 3) {
+          if (/* tag */typeof token$5 === "number") {
+            switch (token$5) {
+              case /* T_CONST */25 :
                   error(env$1, /* DeclareExportConst */51);
-                }
-              }
-              var $$var = declare_var(env$1, start_loc);
-              match$7 = [
-                $$var[0],
-                {
-                  TAG: /* Variable */0,
-                  _0: $$var
-                }
-              ];
-              break;
-          
+                  break;
+              case /* T_LET */26 :
+                  error(env$1, /* DeclareExportLet */50);
+                  break;
+              default:
+                
+            }
+          }
+          var $$var = declare_var(env$1, start_loc);
+          match$7 = [
+            $$var[0],
+            {
+              TAG: /* Variable */0,
+              _0: $$var
+            }
+          ];
         }
         return [
                 btwn(start_loc, match$7[0]),
@@ -11997,7 +12067,10 @@ function supers(env, _acc) {
       tl: acc
     };
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 8) {
+    if (/* tag */typeof match !== "number") {
+      return List.rev(acc$1);
+    }
+    if (match !== /* T_COMMA */8) {
       return List.rev(acc$1);
     }
     token$4(env, /* T_COMMA */8);
@@ -12036,7 +12109,10 @@ function supers$1(env, _acc) {
       tl: acc
     };
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 8) {
+    if (/* tag */typeof match !== "number") {
+      return List.rev(acc$1);
+    }
+    if (match !== /* T_COMMA */8) {
       return List.rev(acc$1);
     }
     token$4(env, /* T_COMMA */8);
@@ -12073,20 +12149,17 @@ function module_items(env, _module_kind, _acc) {
     var acc = _acc;
     var module_kind = _module_kind;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 2) {
-        return [
-                module_kind,
-                List.rev(acc)
-              ];
-      }
-      if (match === 105) {
-        return [
-                module_kind,
-                List.rev(acc)
-              ];
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return [
+                    module_kind,
+                    List.rev(acc)
+                  ];
+        default:
+          
       }
-      
     }
     var stmt = declare(true, env);
     var stmt$1 = stmt[1];
@@ -12094,7 +12167,7 @@ function module_items(env, _module_kind, _acc) {
     var module_kind$1;
     if (module_kind !== undefined) {
       if (module_kind.TAG === /* CommonJS */0) {
-        if (typeof stmt$1 === "number") {
+        if (/* tag */typeof stmt$1 === "number") {
           module_kind$1 = module_kind;
         } else {
           switch (stmt$1.TAG | 0) {
@@ -12121,13 +12194,13 @@ function module_items(env, _module_kind, _acc) {
               module_kind$1 = module_kind;
           }
         }
-      } else if (typeof stmt$1 === "number" || stmt$1.TAG !== /* DeclareModuleExports */26) {
+      } else if (/* tag */typeof stmt$1 === "number" || stmt$1.TAG !== /* DeclareModuleExports */26) {
         module_kind$1 = module_kind;
       } else {
         error(env, /* AmbiguousDeclareModuleKind */61);
         module_kind$1 = module_kind;
       }
-    } else if (typeof stmt$1 === "number") {
+    } else if (/* tag */typeof stmt$1 === "number") {
       module_kind$1 = module_kind;
     } else {
       switch (stmt$1.TAG | 0) {
@@ -12277,31 +12350,43 @@ function case_list(env, _param) {
     var acc = param[1];
     var seen_default = param[0];
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 2) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
     var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
-    var test = match$1 === 34 ? (seen_default ? error(env, /* MultipleDefaultsInSwitch */19) : undefined, token$4(env, /* T_DEFAULT */34), undefined) : (token$4(env, /* T_CASE */31), Curry._1(Parse.expression, env));
+    var test;
+    if (/* tag */typeof match$1 === "number" && match$1 === /* T_DEFAULT */34) {
+      if (seen_default) {
+        error(env, /* MultipleDefaultsInSwitch */19);
+      }
+      token$4(env, /* T_DEFAULT */34);
+      test = undefined;
+    } else {
+      token$4(env, /* T_CASE */31);
+      test = Curry._1(Parse.expression, env);
+    }
     var seen_default$1 = seen_default || test === undefined;
     var end_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
     token$4(env, /* T_COLON */77);
     var term_fn = function (param) {
-      if (typeof param === "number") {
-        if (param > 31 || param < 2) {
-          return param === 34;
-        } else {
-          return param > 30 || param < 3;
-        }
-      } else {
+      if (/* tag */typeof param !== "number") {
         return false;
       }
+      switch (param) {
+        case /* T_RCURLY */2 :
+        case /* T_CASE */31 :
+        case /* T_DEFAULT */34 :
+            return true;
+        default:
+          return false;
+      }
     };
     var consequent = Curry._2(Parse.statement_list, term_fn, with_in_switch(true, env));
     var match$2 = List.rev(consequent);
@@ -12344,7 +12429,7 @@ function var_or_const(env) {
 function source(env) {
   contextual(env, "from");
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number" && match.TAG === /* T_STRING */1) {
+  if (/* tag */typeof match !== "number" && match.TAG === /* T_STRING */1) {
     var match$1 = match._0;
     var octal = match$1[3];
     var raw = match$1[2];
@@ -12396,14 +12481,14 @@ function specifier_list(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match === 2) {
-        return List.rev(acc);
-      }
-      if (match === 105) {
-        return List.rev(acc);
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_RCURLY */2 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
-      
     }
     var match$1 = Curry._1(Parse.identifier_or_reserved_keyword, env);
     var err = match$1[1];
@@ -12445,7 +12530,7 @@ function specifier_list(env, _acc) {
 function named_or_namespace_specifier(env) {
   var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (match === 97) {
+  if (/* tag */typeof match === "number" && match === /* T_MULT */97) {
     token$4(env, /* T_MULT */97);
     contextual(env, "as");
     var id = Curry._2(Parse.identifier, undefined, env);
@@ -12469,7 +12554,7 @@ function named_or_namespace_specifier(env) {
 function from_expr(env, param) {
   var expr = param[1];
   var loc = param[0];
-  if (typeof expr !== "number") {
+  if (/* tag */typeof expr !== "number") {
     switch (expr.TAG | 0) {
       case /* Array */0 :
           var param$1 = [
@@ -12581,7 +12666,7 @@ function from_expr(env, param) {
                 ];
       case /* Assignment */7 :
           var match = expr._0;
-          if (match.operator === 0) {
+          if (match.operator === /* Assign */0) {
             return [
                     loc,
                     {
@@ -12660,13 +12745,17 @@ function _object$2(restricted_error) {
     }
     var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
     var prop;
-    if (match$1 === 77) {
+    var exit = 0;
+    if (/* tag */typeof match$1 === "number" && match$1 === /* T_COLON */77) {
       token$4(env, /* T_COLON */77);
       prop = [
         pattern$1(env, restricted_error),
         false
       ];
     } else {
+      exit = 1;
+    }
+    if (exit === 1) {
       switch (key.TAG | 0) {
         case /* Identifier */1 :
             var id = key._0;
@@ -12698,7 +12787,7 @@ function _object$2(restricted_error) {
     var pattern$3 = prop[0];
     var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
     var pattern$4;
-    if (match$2 === 75) {
+    if (/* tag */typeof match$2 === "number" && match$2 === /* T_ASSIGN */75) {
       token$4(env, /* T_ASSIGN */75);
       var $$default = Curry._1(Parse.assignment, env);
       var loc$1 = btwn(pattern$3[0], $$default[0]);
@@ -12732,14 +12821,14 @@ function _object$2(restricted_error) {
     while(true) {
       var acc = _acc;
       var match = Curry._2(Parser_env_Peek.token, undefined, env);
-      if (typeof match === "number") {
-        if (match === 2) {
-          return List.rev(acc);
-        }
-        if (match === 105) {
-          return List.rev(acc);
+      if (/* tag */typeof match === "number") {
+        switch (match) {
+          case /* T_RCURLY */2 :
+          case /* T_EOF */105 :
+              return List.rev(acc);
+          default:
+            
         }
-        
       }
       var prop = property(env);
       if (prop !== undefined) {
@@ -12792,59 +12881,45 @@ function _array(restricted_error) {
     while(true) {
       var acc = _acc;
       var match = Curry._2(Parser_env_Peek.token, undefined, env);
-      if (typeof match === "number") {
-        if (match === 105) {
-          return List.rev(acc);
-        }
-        if (match < 12) {
-          switch (match) {
-            case /* T_RBRACKET */6 :
-                return List.rev(acc);
-            case /* T_COMMA */8 :
-                token$4(env, /* T_COMMA */8);
-                _acc = {
-                  hd: undefined,
-                  tl: acc
-                };
-                continue ;
-            case /* T_IDENTIFIER */0 :
-            case /* T_LCURLY */1 :
-            case /* T_RCURLY */2 :
-            case /* T_LPAREN */3 :
-            case /* T_RPAREN */4 :
-            case /* T_LBRACKET */5 :
-            case /* T_SEMICOLON */7 :
-            case /* T_PERIOD */9 :
-            case /* T_ARROW */10 :
-                break;
-            case /* T_ELLIPSIS */11 :
-                var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_ELLIPSIS */11);
-                var argument = pattern$1(env, restricted_error);
-                var loc = btwn(start_loc, argument[0]);
-                var element = {
-                  TAG: /* Spread */1,
-                  _0: [
-                    loc,
-                    {
-                      argument: argument
-                    }
-                  ]
-                };
-                _acc = {
-                  hd: element,
-                  tl: acc
-                };
-                continue ;
+      if (/* tag */typeof match === "number") {
+        switch (match) {
+          case /* T_COMMA */8 :
+              token$4(env, /* T_COMMA */8);
+              _acc = {
+                hd: undefined,
+                tl: acc
+              };
+              continue ;
+          case /* T_ELLIPSIS */11 :
+              var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+              token$4(env, /* T_ELLIPSIS */11);
+              var argument = pattern$1(env, restricted_error);
+              var loc = btwn(start_loc, argument[0]);
+              var element = {
+                TAG: /* Spread */1,
+                _0: [
+                  loc,
+                  {
+                    argument: argument
+                  }
+                ]
+              };
+              _acc = {
+                hd: element,
+                tl: acc
+              };
+              continue ;
+          case /* T_RBRACKET */6 :
+          case /* T_EOF */105 :
+              return List.rev(acc);
+          default:
             
-          }
         }
-        
       }
       var pattern$2 = pattern$1(env, restricted_error);
       var match$1 = Curry._2(Parser_env_Peek.token, undefined, env);
       var pattern$3;
-      if (match$1 === 75) {
+      if (/* tag */typeof match$1 === "number" && match$1 === /* T_ASSIGN */75) {
         token$4(env, /* T_ASSIGN */75);
         var $$default = Curry._1(Parse.expression, env);
         var loc$1 = btwn(pattern$2[0], $$default[0]);
@@ -12909,14 +12984,15 @@ function _array(restricted_error) {
 
 function pattern$1(env, restricted_error) {
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match === "number") {
-    if (match === 1) {
-      return _object$2(restricted_error)(env);
-    }
-    if (match === 5) {
-      return _array(restricted_error)(env);
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_LCURLY */1 :
+          return _object$2(restricted_error)(env);
+      case /* T_LBRACKET */5 :
+          return _array(restricted_error)(env);
+      default:
+        
     }
-    
   }
   var id = Curry._2(Parse.identifier_with_type, env, restricted_error);
   return [
@@ -12989,7 +13065,10 @@ function member_expression(env, _member) {
   while(true) {
     var member = _member;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (match !== 9) {
+    if (/* tag */typeof match !== "number") {
+      return member;
+    }
+    if (match !== /* T_PERIOD */9) {
       return member;
     }
     var _object = {
@@ -13015,52 +13094,53 @@ function member_expression(env, _member) {
 function name(env) {
   var name$1 = identifier$1(env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number") {
+  if (/* tag */typeof match !== "number") {
     return {
             TAG: /* Identifier */0,
             _0: name$1
           };
   }
-  if (match !== 9) {
-    if (match !== 77) {
+  switch (match) {
+    case /* T_PERIOD */9 :
+        var _object = {
+          TAG: /* Identifier */0,
+          _0: name$1
+        };
+        token$4(env, /* T_PERIOD */9);
+        var property = identifier$1(env);
+        var loc = btwn(name$1[0], property[0]);
+        var member_1 = {
+          _object: _object,
+          property: property
+        };
+        var member = [
+          loc,
+          member_1
+        ];
+        return {
+                TAG: /* MemberExpression */2,
+                _0: member_expression(env, member)
+              };
+    case /* T_COLON */77 :
+        token$4(env, /* T_COLON */77);
+        var name$2 = identifier$1(env);
+        var loc$1 = btwn(name$1[0], name$2[0]);
+        return {
+                TAG: /* NamespacedName */1,
+                _0: [
+                  loc$1,
+                  {
+                    namespace: name$1,
+                    name: name$2
+                  }
+                ]
+              };
+    default:
       return {
               TAG: /* Identifier */0,
               _0: name$1
             };
-    }
-    token$4(env, /* T_COLON */77);
-    var name$2 = identifier$1(env);
-    var loc = btwn(name$1[0], name$2[0]);
-    return {
-            TAG: /* NamespacedName */1,
-            _0: [
-              loc,
-              {
-                namespace: name$1,
-                name: name$2
-              }
-            ]
-          };
   }
-  var _object = {
-    TAG: /* Identifier */0,
-    _0: name$1
-  };
-  token$4(env, /* T_PERIOD */9);
-  var property = identifier$1(env);
-  var loc$1 = btwn(name$1[0], property[0]);
-  var member_1 = {
-    _object: _object,
-    property: property
-  };
-  var member = [
-    loc$1,
-    member_1
-  ];
-  return {
-          TAG: /* MemberExpression */2,
-          _0: member_expression(env, member)
-        };
 }
 
 function attribute(env) {
@@ -13098,7 +13178,7 @@ function attribute(env) {
     token$4(env, /* T_ASSIGN */75);
     var token$5 = Curry._2(Parser_env_Peek.token, undefined, env);
     var exit = 0;
-    if (typeof token$5 === "number") {
+    if (/* tag */typeof token$5 === "number") {
       if (token$5 === /* T_LCURLY */1) {
         var match$2 = expression_container(env);
         var expression_container$1 = match$2[1];
@@ -13178,30 +13258,24 @@ function attributes(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match >= 91) {
-        if (match === 96) {
-          return List.rev(acc);
-        }
-        if (match === 105) {
-          return List.rev(acc);
-        }
-        
-      } else if (match !== 1) {
-        if (match >= 90) {
-          return List.rev(acc);
-        }
-        
-      } else {
-        var attribute$1 = {
-          TAG: /* SpreadAttribute */1,
-          _0: spread_attribute(env)
-        };
-        _acc = {
-          hd: attribute$1,
-          tl: acc
-        };
-        continue ;
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_LCURLY */1 :
+            var attribute$1 = {
+              TAG: /* SpreadAttribute */1,
+              _0: spread_attribute(env)
+            };
+            _acc = {
+              hd: attribute$1,
+              tl: acc
+            };
+            continue ;
+        case /* T_GREATER_THAN */90 :
+        case /* T_DIV */96 :
+        case /* T_EOF */105 :
+            return List.rev(acc);
+        default:
+          
       }
     }
     var attribute$2 = {
@@ -13252,7 +13326,7 @@ function closing_element_without_lt(env, start_loc) {
 
 function child(env) {
   var token$5 = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof token$5 === "number") {
+  if (/* tag */typeof token$5 === "number") {
     if (token$5 === /* T_LCURLY */1) {
       var expression_container$1 = expression_container(env);
       return [
@@ -13300,66 +13374,76 @@ function element_or_closing(env) {
   var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   token$4(env, /* T_LESS_THAN */89);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match === "number" && !(match !== 96 && match !== 105)) {
-    return {
-            TAG: /* Closing */0,
-            _0: closing_element_without_lt(env, start_loc)
-          };
-  } else {
+  if (/* tag */typeof match !== "number") {
     return {
             TAG: /* ChildElement */1,
             _0: Curry._2(element_without_lt, env, start_loc)
           };
   }
+  switch (match) {
+    case /* T_DIV */96 :
+    case /* T_EOF */105 :
+        return {
+                TAG: /* Closing */0,
+                _0: closing_element_without_lt(env, start_loc)
+              };
+    default:
+      return {
+              TAG: /* ChildElement */1,
+              _0: Curry._2(element_without_lt, env, start_loc)
+            };
+  }
 }
 
 function children_and_closing(env, _acc) {
   while(true) {
     var acc = _acc;
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (typeof match === "number") {
-      if (match !== 89) {
-        if (match !== 105) {
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_LESS_THAN */89 :
+            var closingElement = element_or_closing(env);
+            if (closingElement.TAG === /* Closing */0) {
+              return [
+                      List.rev(acc),
+                      closingElement._0
+                    ];
+            }
+            var element = closingElement._0;
+            var element_0 = element[0];
+            var element_1 = {
+              TAG: /* Element */0,
+              _0: element[1]
+            };
+            var element$1 = [
+              element_0,
+              element_1
+            ];
+            _acc = {
+              hd: element$1,
+              tl: acc
+            };
+            continue ;
+        case /* T_EOF */105 :
+            error_unexpected(env);
+            return [
+                    List.rev(acc),
+                    undefined
+                  ];
+        default:
           _acc = {
             hd: child(env),
             tl: acc
           };
           continue ;
-        }
-        error_unexpected(env);
-        return [
-                List.rev(acc),
-                undefined
-              ];
       }
-      var closingElement = element_or_closing(env);
-      if (closingElement.TAG === /* Closing */0) {
-        return [
-                List.rev(acc),
-                closingElement._0
-              ];
-      }
-      var element = closingElement._0;
-      var element_0 = element[0];
-      var element_1 = {
-        TAG: /* Element */0,
-        _0: element[1]
-      };
-      var element$1 = [
-        element_0,
-        element_1
-      ];
+    } else {
       _acc = {
-        hd: element$1,
+        hd: child(env),
         tl: acc
       };
       continue ;
     }
-    _acc = {
-      hd: child(env),
-      tl: acc
-    };
-    continue ;
   };
 }
 
@@ -13417,411 +13501,364 @@ function statement(env) {
   while(true) {
     var match = Curry._2(Parser_env_Peek.token, undefined, env);
     var exit = 0;
-    if (typeof match === "number") {
-      if (match !== 105) {
-        if (match >= 58) {
-          exit = 2;
-        } else {
-          switch (match) {
-            case /* T_LCURLY */1 :
-                var match$1 = Curry._1(Parse.block_body, env);
-                return [
-                        match$1[0],
-                        {
-                          TAG: /* Block */0,
-                          _0: match$1[1]
-                        }
-                      ];
-            case /* T_SEMICOLON */7 :
-                var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_SEMICOLON */7);
-                return [
-                        loc,
-                        /* Empty */0
-                      ];
-            case /* T_IF */14 :
-                return _if(env);
-            case /* T_RETURN */17 :
-                if (!env.in_function) {
-                  error(env, /* IllegalReturn */23);
-                }
-                var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_RETURN */17);
-                var argument = Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env) ? undefined : Curry._1(Parse.expression, env);
-                var loc$1 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc = loc$1 !== undefined ? loc$1 : (
-                    argument !== undefined ? argument[0] : start_loc
-                  );
-                semicolon(env);
-                return [
-                        btwn(start_loc, end_loc),
-                        {
-                          TAG: /* Return */9,
-                          _0: {
-                            argument: argument
-                          }
-                        }
-                      ];
-            case /* T_SWITCH */18 :
-                var start_loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_SWITCH */18);
-                token$4(env, /* T_LPAREN */3);
-                var discriminant = Curry._1(Parse.expression, env);
-                token$4(env, /* T_RPAREN */4);
-                token$4(env, /* T_LCURLY */1);
-                var cases = case_list(env, [
-                      false,
-                      /* [] */0
-                    ]);
-                var end_loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_RCURLY */2);
-                return [
-                        btwn(start_loc$1, end_loc$1),
-                        {
-                          TAG: /* Switch */8,
-                          _0: {
-                            discriminant: discriminant,
-                            cases: cases,
-                            lexical: false
-                          }
-                        }
-                      ];
-            case /* T_THROW */20 :
-                var start_loc$2 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_THROW */20);
-                if (Curry._1(Parser_env_Peek.is_line_terminator, env)) {
-                  error_at(env, [
-                        start_loc$2,
-                        /* NewlineAfterThrow */11
-                      ]);
-                }
-                var argument$1 = Curry._1(Parse.expression, env);
-                var loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc$2 = loc$2 !== undefined ? loc$2 : argument$1[0];
-                semicolon(env);
-                return [
-                        btwn(start_loc$2, end_loc$2),
-                        {
-                          TAG: /* Throw */10,
-                          _0: {
-                            argument: argument$1
-                          }
-                        }
-                      ];
-            case /* T_TRY */21 :
-                var start_loc$3 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_TRY */21);
-                var block = Curry._1(Parse.block_body, env);
-                var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
-                var handler;
-                if (match$2 === 32) {
-                  var start_loc$4 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                  token$4(env, /* T_CATCH */32);
-                  token$4(env, /* T_LPAREN */3);
-                  var id = Curry._2(Parse.identifier, /* StrictCatchVariable */26, env);
-                  var param_0 = id[0];
-                  var param_1 = {
-                    TAG: /* Identifier */3,
-                    _0: id
-                  };
-                  var param = [
-                    param_0,
-                    param_1
+    if (/* tag */typeof match === "number") {
+      switch (match) {
+        case /* T_LCURLY */1 :
+            var match$1 = Curry._1(Parse.block_body, env);
+            return [
+                    match$1[0],
+                    {
+                      TAG: /* Block */0,
+                      _0: match$1[1]
+                    }
                   ];
-                  token$4(env, /* T_RPAREN */4);
-                  var body = Curry._1(Parse.block_body, env);
-                  var loc$3 = btwn(start_loc$4, body[0]);
-                  handler = [
-                    loc$3,
+        case /* T_SEMICOLON */7 :
+            var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_SEMICOLON */7);
+            return [
+                    loc,
+                    /* Empty */0
+                  ];
+        case /* T_IF */14 :
+            return _if(env);
+        case /* T_RETURN */17 :
+            if (!env.in_function) {
+              error(env, /* IllegalReturn */23);
+            }
+            var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_RETURN */17);
+            var argument = Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env) ? undefined : Curry._1(Parse.expression, env);
+            var loc$1 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc = loc$1 !== undefined ? loc$1 : (
+                argument !== undefined ? argument[0] : start_loc
+              );
+            semicolon(env);
+            return [
+                    btwn(start_loc, end_loc),
                     {
-                      param: param,
-                      guard: undefined,
-                      body: body
+                      TAG: /* Return */9,
+                      _0: {
+                        argument: argument
+                      }
                     }
                   ];
-                } else {
-                  handler = undefined;
-                }
-                var match$3 = Curry._2(Parser_env_Peek.token, undefined, env);
-                var finalizer = match$3 === 36 ? (token$4(env, /* T_FINALLY */36), Curry._1(Parse.block_body, env)) : undefined;
-                var end_loc$3 = finalizer !== undefined ? finalizer[0] : (
-                    handler !== undefined ? handler[0] : (error_at(env, [
-                              block[0],
-                              /* NoCatchOrFinally */20
-                            ]), block[0])
-                  );
-                return [
-                        btwn(start_loc$3, end_loc$3),
-                        {
-                          TAG: /* Try */11,
-                          _0: {
-                            block: block,
-                            handler: handler,
-                            guardedHandlers: /* [] */0,
-                            finalizer: finalizer
-                          }
-                        }
-                      ];
-            case /* T_VAR */22 :
-                return var_or_const(env);
-            case /* T_WHILE */23 :
-                var start_loc$5 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_WHILE */23);
-                token$4(env, /* T_LPAREN */3);
-                var test = Curry._1(Parse.expression, env);
-                token$4(env, /* T_RPAREN */4);
-                var body$1 = Curry._1(Parse.statement, with_in_loop(true, env));
-                return [
-                        btwn(start_loc$5, body$1[0]),
-                        {
-                          TAG: /* While */12,
-                          _0: {
-                            test: test,
-                            body: body$1
-                          }
-                        }
-                      ];
-            case /* T_WITH */24 :
-                var start_loc$6 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_WITH */24);
-                token$4(env, /* T_LPAREN */3);
-                var _object = Curry._1(Parse.expression, env);
-                token$4(env, /* T_RPAREN */4);
-                var body$2 = Curry._1(Parse.statement, env);
-                var loc$4 = btwn(start_loc$6, body$2[0]);
-                strict_error_at(env, [
-                      loc$4,
-                      /* StrictModeWith */25
-                    ]);
-                return [
-                        loc$4,
-                        {
-                          TAG: /* With */6,
-                          _0: {
-                            _object: _object,
-                            body: body$2
-                          }
-                        }
-                      ];
-            case /* T_BREAK */30 :
-                var start_loc$7 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_BREAK */30);
-                var label;
-                if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env)) {
-                  label = undefined;
-                } else {
-                  var label$1 = Curry._2(Parse.identifier, undefined, env);
-                  var name = label$1[1].name;
-                  if (!mem$1(name, env.labels)) {
-                    error(env, {
-                          TAG: /* UnknownLabel */4,
-                          _0: name
-                        });
-                  }
-                  label = label$1;
-                }
-                var loc$5 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc$4 = loc$5 !== undefined ? loc$5 : (
-                    label !== undefined ? label[0] : start_loc$7
-                  );
-                var loc$6 = btwn(start_loc$7, end_loc$4);
-                if (label === undefined && !(env.in_loop || env.in_switch)) {
-                  error_at(env, [
-                        loc$6,
-                        /* IllegalBreak */22
-                      ]);
-                }
-                semicolon(env);
-                return [
-                        loc$6,
-                        {
-                          TAG: /* Break */4,
-                          _0: {
-                            label: label
-                          }
-                        }
-                      ];
-            case /* T_CONTINUE */33 :
-                var start_loc$8 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_CONTINUE */33);
-                var label$2;
-                if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env)) {
-                  label$2 = undefined;
-                } else {
-                  var label$3 = Curry._2(Parse.identifier, undefined, env);
-                  var name$1 = label$3[1].name;
-                  if (!mem$1(name$1, env.labels)) {
-                    error(env, {
-                          TAG: /* UnknownLabel */4,
-                          _0: name$1
-                        });
-                  }
-                  label$2 = label$3;
-                }
-                var loc$7 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc$5 = loc$7 !== undefined ? loc$7 : (
-                    label$2 !== undefined ? label$2[0] : start_loc$8
-                  );
-                var loc$8 = btwn(start_loc$8, end_loc$5);
-                if (!env.in_loop) {
-                  error_at(env, [
-                        loc$8,
-                        /* IllegalContinue */21
-                      ]);
-                }
-                semicolon(env);
-                return [
-                        loc$8,
-                        {
-                          TAG: /* Continue */5,
-                          _0: {
-                            label: label$2
-                          }
-                        }
-                      ];
-            case /* T_DO */35 :
-                var start_loc$9 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_DO */35);
-                var body$3 = Curry._1(Parse.statement, with_in_loop(true, env));
-                token$4(env, /* T_WHILE */23);
-                token$4(env, /* T_LPAREN */3);
-                var test$1 = Curry._1(Parse.expression, env);
-                var end_loc$6 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_RPAREN */4);
-                var loc$9 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc$7 = loc$9 !== undefined ? loc$9 : end_loc$6;
-                if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7) {
-                  semicolon(env);
+        case /* T_SWITCH */18 :
+            var start_loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_SWITCH */18);
+            token$4(env, /* T_LPAREN */3);
+            var discriminant = Curry._1(Parse.expression, env);
+            token$4(env, /* T_RPAREN */4);
+            token$4(env, /* T_LCURLY */1);
+            var cases = case_list(env, [
+                  false,
+                  /* [] */0
+                ]);
+            var end_loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_RCURLY */2);
+            return [
+                    btwn(start_loc$1, end_loc$1),
+                    {
+                      TAG: /* Switch */8,
+                      _0: {
+                        discriminant: discriminant,
+                        cases: cases,
+                        lexical: false
+                      }
+                    }
+                  ];
+        case /* T_THROW */20 :
+            var start_loc$2 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_THROW */20);
+            if (Curry._1(Parser_env_Peek.is_line_terminator, env)) {
+              error_at(env, [
+                    start_loc$2,
+                    /* NewlineAfterThrow */11
+                  ]);
+            }
+            var argument$1 = Curry._1(Parse.expression, env);
+            var loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$2 = loc$2 !== undefined ? loc$2 : argument$1[0];
+            semicolon(env);
+            return [
+                    btwn(start_loc$2, end_loc$2),
+                    {
+                      TAG: /* Throw */10,
+                      _0: {
+                        argument: argument$1
+                      }
+                    }
+                  ];
+        case /* T_TRY */21 :
+            var start_loc$3 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_TRY */21);
+            var block = Curry._1(Parse.block_body, env);
+            var match$2 = Curry._2(Parser_env_Peek.token, undefined, env);
+            var handler;
+            if (/* tag */typeof match$2 === "number" && match$2 === /* T_CATCH */32) {
+              var start_loc$4 = Curry._2(Parser_env_Peek.loc, undefined, env);
+              token$4(env, /* T_CATCH */32);
+              token$4(env, /* T_LPAREN */3);
+              var id = Curry._2(Parse.identifier, /* StrictCatchVariable */26, env);
+              var param_0 = id[0];
+              var param_1 = {
+                TAG: /* Identifier */3,
+                _0: id
+              };
+              var param = [
+                param_0,
+                param_1
+              ];
+              token$4(env, /* T_RPAREN */4);
+              var body = Curry._1(Parse.block_body, env);
+              var loc$3 = btwn(start_loc$4, body[0]);
+              handler = [
+                loc$3,
+                {
+                  param: param,
+                  guard: undefined,
+                  body: body
                 }
-                return [
-                        btwn(start_loc$9, end_loc$7),
-                        {
-                          TAG: /* DoWhile */13,
-                          _0: {
-                            body: body$3,
-                            test: test$1
-                          }
-                        }
-                      ];
-            case /* T_FOR */37 :
-                var start_loc$10 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_FOR */37);
-                token$4(env, /* T_LPAREN */3);
-                var match$4 = Curry._2(Parser_env_Peek.token, undefined, env);
-                var match$5;
-                var exit$1 = 0;
-                if (typeof match$4 === "number") {
-                  if (match$4 >= 22) {
-                    if (match$4 >= 27) {
-                      exit$1 = 1;
-                    } else {
-                      switch (match$4) {
-                        case /* T_VAR */22 :
-                            var match$6 = declarations(/* T_VAR */22, /* Var */0, with_no_in(true, env));
-                            match$5 = [
-                              {
-                                TAG: /* InitDeclaration */0,
-                                _0: match$6[0]
-                              },
-                              match$6[1]
-                            ];
-                            break;
-                        case /* T_WHILE */23 :
-                        case /* T_WITH */24 :
-                            exit$1 = 1;
-                            break;
-                        case /* T_CONST */25 :
-                            var match$7 = $$const(with_no_in(true, env));
-                            match$5 = [
-                              {
-                                TAG: /* InitDeclaration */0,
-                                _0: match$7[0]
-                              },
-                              match$7[1]
-                            ];
-                            break;
-                        case /* T_LET */26 :
-                            var match$8 = _let(with_no_in(true, env));
-                            match$5 = [
-                              {
-                                TAG: /* InitDeclaration */0,
-                                _0: match$8[0]
-                              },
-                              match$8[1]
-                            ];
-                            break;
-                        
+              ];
+            } else {
+              handler = undefined;
+            }
+            var match$3 = Curry._2(Parser_env_Peek.token, undefined, env);
+            var finalizer;
+            if (/* tag */typeof match$3 === "number" && match$3 === /* T_FINALLY */36) {
+              token$4(env, /* T_FINALLY */36);
+              finalizer = Curry._1(Parse.block_body, env);
+            } else {
+              finalizer = undefined;
+            }
+            var end_loc$3 = finalizer !== undefined ? finalizer[0] : (
+                handler !== undefined ? handler[0] : (error_at(env, [
+                          block[0],
+                          /* NoCatchOrFinally */20
+                        ]), block[0])
+              );
+            return [
+                    btwn(start_loc$3, end_loc$3),
+                    {
+                      TAG: /* Try */11,
+                      _0: {
+                        block: block,
+                        handler: handler,
+                        guardedHandlers: /* [] */0,
+                        finalizer: finalizer
                       }
                     }
-                  } else if (match$4 !== 7) {
-                    exit$1 = 1;
-                  } else {
+                  ];
+        case /* T_VAR */22 :
+            return var_or_const(env);
+        case /* T_WHILE */23 :
+            var start_loc$5 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_WHILE */23);
+            token$4(env, /* T_LPAREN */3);
+            var test = Curry._1(Parse.expression, env);
+            token$4(env, /* T_RPAREN */4);
+            var body$1 = Curry._1(Parse.statement, with_in_loop(true, env));
+            return [
+                    btwn(start_loc$5, body$1[0]),
+                    {
+                      TAG: /* While */12,
+                      _0: {
+                        test: test,
+                        body: body$1
+                      }
+                    }
+                  ];
+        case /* T_WITH */24 :
+            var start_loc$6 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_WITH */24);
+            token$4(env, /* T_LPAREN */3);
+            var _object = Curry._1(Parse.expression, env);
+            token$4(env, /* T_RPAREN */4);
+            var body$2 = Curry._1(Parse.statement, env);
+            var loc$4 = btwn(start_loc$6, body$2[0]);
+            strict_error_at(env, [
+                  loc$4,
+                  /* StrictModeWith */25
+                ]);
+            return [
+                    loc$4,
+                    {
+                      TAG: /* With */6,
+                      _0: {
+                        _object: _object,
+                        body: body$2
+                      }
+                    }
+                  ];
+        case /* T_BREAK */30 :
+            var start_loc$7 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_BREAK */30);
+            var label;
+            if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env)) {
+              label = undefined;
+            } else {
+              var label$1 = Curry._2(Parse.identifier, undefined, env);
+              var name = label$1[1].name;
+              if (!mem$1(name, env.labels)) {
+                error(env, {
+                      TAG: /* UnknownLabel */4,
+                      _0: name
+                    });
+              }
+              label = label$1;
+            }
+            var loc$5 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$4 = loc$5 !== undefined ? loc$5 : (
+                label !== undefined ? label[0] : start_loc$7
+              );
+            var loc$6 = btwn(start_loc$7, end_loc$4);
+            if (label === undefined && !(env.in_loop || env.in_switch)) {
+              error_at(env, [
+                    loc$6,
+                    /* IllegalBreak */22
+                  ]);
+            }
+            semicolon(env);
+            return [
+                    loc$6,
+                    {
+                      TAG: /* Break */4,
+                      _0: {
+                        label: label
+                      }
+                    }
+                  ];
+        case /* T_CONTINUE */33 :
+            var start_loc$8 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_CONTINUE */33);
+            var label$2;
+            if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7 || Curry._1(Parser_env_Peek.is_implicit_semicolon, env)) {
+              label$2 = undefined;
+            } else {
+              var label$3 = Curry._2(Parse.identifier, undefined, env);
+              var name$1 = label$3[1].name;
+              if (!mem$1(name$1, env.labels)) {
+                error(env, {
+                      TAG: /* UnknownLabel */4,
+                      _0: name$1
+                    });
+              }
+              label$2 = label$3;
+            }
+            var loc$7 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$5 = loc$7 !== undefined ? loc$7 : (
+                label$2 !== undefined ? label$2[0] : start_loc$8
+              );
+            var loc$8 = btwn(start_loc$8, end_loc$5);
+            if (!env.in_loop) {
+              error_at(env, [
+                    loc$8,
+                    /* IllegalContinue */21
+                  ]);
+            }
+            semicolon(env);
+            return [
+                    loc$8,
+                    {
+                      TAG: /* Continue */5,
+                      _0: {
+                        label: label$2
+                      }
+                    }
+                  ];
+        case /* T_DO */35 :
+            var start_loc$9 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_DO */35);
+            var body$3 = Curry._1(Parse.statement, with_in_loop(true, env));
+            token$4(env, /* T_WHILE */23);
+            token$4(env, /* T_LPAREN */3);
+            var test$1 = Curry._1(Parse.expression, env);
+            var end_loc$6 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_RPAREN */4);
+            var loc$9 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$7 = loc$9 !== undefined ? loc$9 : end_loc$6;
+            if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_SEMICOLON */7) {
+              semicolon(env);
+            }
+            return [
+                    btwn(start_loc$9, end_loc$7),
+                    {
+                      TAG: /* DoWhile */13,
+                      _0: {
+                        body: body$3,
+                        test: test$1
+                      }
+                    }
+                  ];
+        case /* T_FOR */37 :
+            var start_loc$10 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_FOR */37);
+            token$4(env, /* T_LPAREN */3);
+            var match$4 = Curry._2(Parser_env_Peek.token, undefined, env);
+            var match$5;
+            var exit$1 = 0;
+            if (/* tag */typeof match$4 === "number") {
+              switch (match$4) {
+                case /* T_SEMICOLON */7 :
                     match$5 = [
                       undefined,
                       /* [] */0
                     ];
-                  }
-                } else {
+                    break;
+                case /* T_VAR */22 :
+                    var match$6 = declarations(/* T_VAR */22, /* Var */0, with_no_in(true, env));
+                    match$5 = [
+                      {
+                        TAG: /* InitDeclaration */0,
+                        _0: match$6[0]
+                      },
+                      match$6[1]
+                    ];
+                    break;
+                case /* T_CONST */25 :
+                    var match$7 = $$const(with_no_in(true, env));
+                    match$5 = [
+                      {
+                        TAG: /* InitDeclaration */0,
+                        _0: match$7[0]
+                      },
+                      match$7[1]
+                    ];
+                    break;
+                case /* T_LET */26 :
+                    var match$8 = _let(with_no_in(true, env));
+                    match$5 = [
+                      {
+                        TAG: /* InitDeclaration */0,
+                        _0: match$8[0]
+                      },
+                      match$8[1]
+                    ];
+                    break;
+                default:
                   exit$1 = 1;
-                }
-                if (exit$1 === 1) {
-                  var expr = Curry._1(Parse.expression, with_no_let(true, with_no_in(true, env)));
-                  match$5 = [
-                    {
-                      TAG: /* InitExpression */1,
-                      _0: expr
-                    },
-                    /* [] */0
-                  ];
-                }
-                var init = match$5[0];
-                var match$9 = Curry._2(Parser_env_Peek.token, undefined, env);
-                if (typeof match$9 === "number") {
-                  if (match$9 !== 15) {
-                    if (match$9 === 60) {
-                      assert_can_be_forin_or_forof(env, /* InvalidLHSInForOf */17, init);
-                      var left;
-                      if (init !== undefined) {
-                        left = init.TAG === /* InitDeclaration */0 ? ({
-                              TAG: /* LeftDeclaration */0,
-                              _0: init._0
-                            }) : ({
-                              TAG: /* LeftExpression */1,
-                              _0: init._0
-                            });
-                      } else {
-                        throw {
-                              RE_EXN_ID: "Assert_failure",
-                              _1: [
-                                "parser_flow.ml",
-                                2573,
-                                22
-                              ],
-                              Error: new Error()
-                            };
-                      }
-                      token$4(env, /* T_OF */60);
-                      var right = Curry._1(Parse.assignment, env);
-                      token$4(env, /* T_RPAREN */4);
-                      var body$4 = Curry._1(Parse.statement, with_in_loop(true, env));
-                      return [
-                              btwn(start_loc$10, body$4[0]),
-                              {
-                                TAG: /* ForOf */16,
-                                _0: {
-                                  left: left,
-                                  right: right,
-                                  body: body$4
-                                }
-                              }
-                            ];
-                    }
-                    
-                  } else {
+              }
+            } else {
+              exit$1 = 1;
+            }
+            if (exit$1 === 1) {
+              var expr = Curry._1(Parse.expression, with_no_let(true, with_no_in(true, env)));
+              match$5 = [
+                {
+                  TAG: /* InitExpression */1,
+                  _0: expr
+                },
+                /* [] */0
+              ];
+            }
+            var init = match$5[0];
+            var match$9 = Curry._2(Parser_env_Peek.token, undefined, env);
+            if (/* tag */typeof match$9 === "number") {
+              switch (match$9) {
+                case /* T_IN */15 :
                     assert_can_be_forin_or_forof(env, /* InvalidLHSInForIn */16, init);
-                    var left$1;
+                    var left;
                     if (init !== undefined) {
-                      left$1 = init.TAG === /* InitDeclaration */0 ? ({
+                      left = init.TAG === /* InitDeclaration */0 ? ({
                             TAG: /* LeftDeclaration */0,
                             _0: init._0
                           }) : ({
@@ -13840,110 +13877,105 @@ function statement(env) {
                           };
                     }
                     token$4(env, /* T_IN */15);
-                    var right$1 = Curry._1(Parse.expression, env);
+                    var right = Curry._1(Parse.expression, env);
+                    token$4(env, /* T_RPAREN */4);
+                    var body$4 = Curry._1(Parse.statement, with_in_loop(true, env));
+                    return [
+                            btwn(start_loc$10, body$4[0]),
+                            {
+                              TAG: /* ForIn */15,
+                              _0: {
+                                left: left,
+                                right: right,
+                                body: body$4,
+                                each: false
+                              }
+                            }
+                          ];
+                case /* T_OF */60 :
+                    assert_can_be_forin_or_forof(env, /* InvalidLHSInForOf */17, init);
+                    var left$1;
+                    if (init !== undefined) {
+                      left$1 = init.TAG === /* InitDeclaration */0 ? ({
+                            TAG: /* LeftDeclaration */0,
+                            _0: init._0
+                          }) : ({
+                            TAG: /* LeftExpression */1,
+                            _0: init._0
+                          });
+                    } else {
+                      throw {
+                            RE_EXN_ID: "Assert_failure",
+                            _1: [
+                              "parser_flow.ml",
+                              2573,
+                              22
+                            ],
+                            Error: new Error()
+                          };
+                    }
+                    token$4(env, /* T_OF */60);
+                    var right$1 = Curry._1(Parse.assignment, env);
                     token$4(env, /* T_RPAREN */4);
                     var body$5 = Curry._1(Parse.statement, with_in_loop(true, env));
                     return [
                             btwn(start_loc$10, body$5[0]),
                             {
-                              TAG: /* ForIn */15,
+                              TAG: /* ForOf */16,
                               _0: {
                                 left: left$1,
                                 right: right$1,
-                                body: body$5,
-                                each: false
+                                body: body$5
                               }
                             }
                           ];
-                  }
-                }
-                List.iter((function (param) {
-                        return error_at(env, param);
-                      }), match$5[1]);
-                token$4(env, /* T_SEMICOLON */7);
-                var match$10 = Curry._2(Parser_env_Peek.token, undefined, env);
-                var test$2 = match$10 === 7 ? undefined : Curry._1(Parse.expression, env);
-                token$4(env, /* T_SEMICOLON */7);
-                var match$11 = Curry._2(Parser_env_Peek.token, undefined, env);
-                var update = match$11 === 4 ? undefined : Curry._1(Parse.expression, env);
-                token$4(env, /* T_RPAREN */4);
-                var body$6 = Curry._1(Parse.statement, with_in_loop(true, env));
-                return [
-                        btwn(start_loc$10, body$6[0]),
-                        {
-                          TAG: /* For */14,
-                          _0: {
-                            init: init,
-                            test: test$2,
-                            update: update,
-                            body: body$6
-                          }
-                        }
-                      ];
-            case /* T_IDENTIFIER */0 :
-            case /* T_RCURLY */2 :
-            case /* T_LPAREN */3 :
-            case /* T_RPAREN */4 :
-            case /* T_LBRACKET */5 :
-            case /* T_RBRACKET */6 :
-            case /* T_COMMA */8 :
-            case /* T_PERIOD */9 :
-            case /* T_ARROW */10 :
-            case /* T_ELLIPSIS */11 :
-            case /* T_AT */12 :
-            case /* T_FUNCTION */13 :
-            case /* T_IN */15 :
-            case /* T_INSTANCEOF */16 :
-            case /* T_THIS */19 :
-            case /* T_CONST */25 :
-            case /* T_LET */26 :
-            case /* T_NULL */27 :
-            case /* T_FALSE */28 :
-            case /* T_TRUE */29 :
-            case /* T_CASE */31 :
-            case /* T_CATCH */32 :
-            case /* T_DEFAULT */34 :
-            case /* T_FINALLY */36 :
-            case /* T_CLASS */38 :
-            case /* T_EXTENDS */39 :
-            case /* T_STATIC */40 :
-            case /* T_ELSE */41 :
-            case /* T_NEW */42 :
-            case /* T_DELETE */43 :
-            case /* T_TYPEOF */44 :
-            case /* T_VOID */45 :
-            case /* T_ENUM */46 :
-            case /* T_EXPORT */47 :
-            case /* T_IMPORT */48 :
-            case /* T_SUPER */49 :
-            case /* T_IMPLEMENTS */50 :
-            case /* T_INTERFACE */51 :
-            case /* T_PACKAGE */52 :
-            case /* T_PRIVATE */53 :
-            case /* T_PROTECTED */54 :
-            case /* T_PUBLIC */55 :
-            case /* T_YIELD */56 :
-                exit = 2;
-                break;
-            case /* T_DEBUGGER */57 :
-                var start_loc$11 = Curry._2(Parser_env_Peek.loc, undefined, env);
-                token$4(env, /* T_DEBUGGER */57);
-                var loc$10 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-                var end_loc$8 = loc$10 !== undefined ? loc$10 : start_loc$11;
-                semicolon(env);
-                return [
-                        btwn(start_loc$11, end_loc$8),
-                        /* Debugger */1
-                      ];
-            
-          }
-        }
-      } else {
-        error_unexpected(env);
-        return [
-                Curry._2(Parser_env_Peek.loc, undefined, env),
-                /* Empty */0
-              ];
+                default:
+                  
+              }
+            }
+            List.iter((function (param) {
+                    return error_at(env, param);
+                  }), match$5[1]);
+            token$4(env, /* T_SEMICOLON */7);
+            var match$10 = Curry._2(Parser_env_Peek.token, undefined, env);
+            var test$2;
+            test$2 = /* tag */typeof match$10 === "number" && match$10 === /* T_SEMICOLON */7 ? undefined : Curry._1(Parse.expression, env);
+            token$4(env, /* T_SEMICOLON */7);
+            var match$11 = Curry._2(Parser_env_Peek.token, undefined, env);
+            var update;
+            update = /* tag */typeof match$11 === "number" && match$11 === /* T_RPAREN */4 ? undefined : Curry._1(Parse.expression, env);
+            token$4(env, /* T_RPAREN */4);
+            var body$6 = Curry._1(Parse.statement, with_in_loop(true, env));
+            return [
+                    btwn(start_loc$10, body$6[0]),
+                    {
+                      TAG: /* For */14,
+                      _0: {
+                        init: init,
+                        test: test$2,
+                        update: update,
+                        body: body$6
+                      }
+                    }
+                  ];
+        case /* T_DEBUGGER */57 :
+            var start_loc$11 = Curry._2(Parser_env_Peek.loc, undefined, env);
+            token$4(env, /* T_DEBUGGER */57);
+            var loc$10 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$8 = loc$10 !== undefined ? loc$10 : start_loc$11;
+            semicolon(env);
+            return [
+                    btwn(start_loc$11, end_loc$8),
+                    /* Debugger */1
+                  ];
+        case /* T_EOF */105 :
+            error_unexpected(env);
+            return [
+                    Curry._2(Parser_env_Peek.loc, undefined, env),
+                    /* Empty */0
+                  ];
+        default:
+          exit = 2;
       }
     } else {
       exit = 2;
@@ -13954,7 +13986,7 @@ function statement(env) {
         var match$12 = Curry._2(Parser_env_Peek.token, undefined, env);
         var label$4 = expr$1[1];
         var loc$11 = expr$1[0];
-        if (typeof label$4 !== "number" && label$4.TAG === /* Identifier */18 && match$12 === 77) {
+        if (/* tag */typeof label$4 !== "number" && label$4.TAG === /* Identifier */18 && /* tag */typeof match$12 === "number" && match$12 === /* T_COLON */77) {
           var label$5 = label$4._0;
           var match$13 = label$5[1];
           var name$2 = match$13.name;
@@ -13995,70 +14027,34 @@ function statement(env) {
                 }
               ];
       }
-      if (typeof match !== "number") {
+      if (/* tag */typeof match !== "number") {
         return expression(env);
       }
-      if (match !== 77) {
-        if (match >= 49) {
+      switch (match) {
+        case /* T_ELSE */41 :
+            return _if(env);
+        case /* T_RCURLY */2 :
+        case /* T_RPAREN */4 :
+        case /* T_RBRACKET */6 :
+        case /* T_COMMA */8 :
+        case /* T_PERIOD */9 :
+        case /* T_ARROW */10 :
+        case /* T_ELLIPSIS */11 :
+        case /* T_IN */15 :
+        case /* T_INSTANCEOF */16 :
+        case /* T_CASE */31 :
+        case /* T_CATCH */32 :
+        case /* T_DEFAULT */34 :
+        case /* T_FINALLY */36 :
+        case /* T_EXTENDS */39 :
+        case /* T_STATIC */40 :
+        case /* T_EXPORT */47 :
+        case /* T_IMPORT */48 :
+        case /* T_COLON */77 :
+            break;
+        default:
           return expression(env);
-        }
-        switch (match) {
-          case /* T_ELSE */41 :
-              return _if(env);
-          case /* T_IDENTIFIER */0 :
-          case /* T_LCURLY */1 :
-          case /* T_LPAREN */3 :
-          case /* T_LBRACKET */5 :
-          case /* T_SEMICOLON */7 :
-          case /* T_AT */12 :
-          case /* T_FUNCTION */13 :
-          case /* T_IF */14 :
-          case /* T_RETURN */17 :
-          case /* T_SWITCH */18 :
-          case /* T_THIS */19 :
-          case /* T_THROW */20 :
-          case /* T_TRY */21 :
-          case /* T_VAR */22 :
-          case /* T_WHILE */23 :
-          case /* T_WITH */24 :
-          case /* T_CONST */25 :
-          case /* T_LET */26 :
-          case /* T_NULL */27 :
-          case /* T_FALSE */28 :
-          case /* T_TRUE */29 :
-          case /* T_BREAK */30 :
-          case /* T_CONTINUE */33 :
-          case /* T_DO */35 :
-          case /* T_FOR */37 :
-          case /* T_CLASS */38 :
-          case /* T_NEW */42 :
-          case /* T_DELETE */43 :
-          case /* T_TYPEOF */44 :
-          case /* T_VOID */45 :
-          case /* T_ENUM */46 :
-              return expression(env);
-          case /* T_RCURLY */2 :
-          case /* T_RPAREN */4 :
-          case /* T_RBRACKET */6 :
-          case /* T_COMMA */8 :
-          case /* T_PERIOD */9 :
-          case /* T_ARROW */10 :
-          case /* T_ELLIPSIS */11 :
-          case /* T_IN */15 :
-          case /* T_INSTANCEOF */16 :
-          case /* T_CASE */31 :
-          case /* T_CATCH */32 :
-          case /* T_DEFAULT */34 :
-          case /* T_FINALLY */36 :
-          case /* T_EXTENDS */39 :
-          case /* T_STATIC */40 :
-          case /* T_EXPORT */47 :
-          case /* T_IMPORT */48 :
-              break;
-          
-        }
       }
-      
     }
     error_unexpected(env);
     token$3(env);
@@ -14069,7 +14065,7 @@ function statement(env) {
 function module_item(env) {
   var decorators = decorator_list(env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match !== "number") {
+  if (/* tag */typeof match !== "number") {
     return statement_list_item(decorators, env);
   }
   switch (match) {
@@ -14079,168 +14075,33 @@ function module_item(env) {
         token$4(env$1, /* T_EXPORT */47);
         var match$1 = Curry._2(Parser_env_Peek.token, undefined, env$1);
         var exit = 0;
-        if (typeof match$1 === "number") {
-          if (match$1 >= 51) {
-            if (match$1 !== 97) {
-              if (match$1 >= 62) {
-                exit = 1;
-              } else {
-                switch (match$1) {
-                  case /* T_INTERFACE */51 :
-                      if (!env$1.parse_options.types) {
-                        error(env$1, /* UnexpectedTypeExport */9);
-                      }
-                      var $$interface$1 = $$interface(env$1);
-                      var match$2 = $$interface$1[1];
-                      if (typeof match$2 === "number") {
-                        throw {
-                              RE_EXN_ID: "Failure",
-                              _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
-                              Error: new Error()
-                            };
-                      }
-                      if (match$2.TAG === /* InterfaceDeclaration */21) {
-                        record_export(env$1, [
-                              $$interface$1[0],
-                              extract_ident_name(match$2._0.id)
-                            ]);
-                      } else {
-                        throw {
-                              RE_EXN_ID: "Failure",
-                              _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
-                              Error: new Error()
-                            };
-                      }
-                      var end_loc = $$interface$1[0];
-                      return [
-                              btwn(start_loc, end_loc),
-                              {
-                                TAG: /* ExportDeclaration */28,
-                                _0: {
-                                  default: false,
-                                  declaration: {
-                                    TAG: /* Declaration */0,
-                                    _0: $$interface$1
-                                  },
-                                  specifiers: undefined,
-                                  source: undefined,
-                                  exportKind: /* ExportType */0
-                                }
-                              }
-                            ];
-                  case /* T_TYPE */59 :
-                      if (Curry._2(Parser_env_Peek.token, 1, env$1) !== /* T_LCURLY */1) {
-                        if (!env$1.parse_options.types) {
-                          error(env$1, /* UnexpectedTypeExport */9);
-                        }
-                        var type_alias$1 = type_alias(env$1);
-                        var match$3 = type_alias$1[1];
-                        if (typeof match$3 === "number") {
-                          throw {
-                                RE_EXN_ID: "Failure",
-                                _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
-                                Error: new Error()
-                              };
-                        }
-                        if (match$3.TAG === /* TypeAlias */7) {
-                          record_export(env$1, [
-                                type_alias$1[0],
-                                extract_ident_name(match$3._0.id)
-                              ]);
-                        } else {
-                          throw {
-                                RE_EXN_ID: "Failure",
-                                _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
-                                Error: new Error()
-                              };
-                        }
-                        var end_loc$1 = type_alias$1[0];
-                        return [
-                                btwn(start_loc, end_loc$1),
-                                {
-                                  TAG: /* ExportDeclaration */28,
-                                  _0: {
-                                    default: false,
-                                    declaration: {
-                                      TAG: /* Declaration */0,
-                                      _0: type_alias$1
-                                    },
-                                    specifiers: undefined,
-                                    source: undefined,
-                                    exportKind: /* ExportType */0
-                                  }
-                                }
-                              ];
-                      }
-                      exit = 1;
-                      break;
-                  case /* T_PACKAGE */52 :
-                  case /* T_PRIVATE */53 :
-                  case /* T_PROTECTED */54 :
-                  case /* T_PUBLIC */55 :
-                  case /* T_YIELD */56 :
-                  case /* T_DEBUGGER */57 :
-                  case /* T_DECLARE */58 :
-                  case /* T_OF */60 :
-                      exit = 1;
-                      break;
-                  case /* T_ASYNC */61 :
-                      exit = 2;
-                      break;
-                  
+        if (/* tag */typeof match$1 === "number") {
+          switch (match$1) {
+            case /* T_DEFAULT */34 :
+                token$4(env$1, /* T_DEFAULT */34);
+                record_export(env$1, [
+                      btwn(start_loc, Curry._2(Parser_env_Peek.loc, undefined, env$1)),
+                      "default"
+                    ]);
+                var match$2 = Curry._2(Parser_env_Peek.token, undefined, env$1);
+                var match$3;
+                var exit$1 = 0;
+                if (/* tag */typeof match$2 === "number" && match$2 === /* T_FUNCTION */13) {
+                  var fn = _function(env$1);
+                  match$3 = [
+                    fn[0],
+                    {
+                      TAG: /* Declaration */0,
+                      _0: fn
+                    }
+                  ];
+                } else {
+                  exit$1 = 3;
                 }
-              }
-            } else {
-              var loc = Curry._2(Parser_env_Peek.loc, undefined, env$1);
-              token$4(env$1, /* T_MULT */97);
-              var parse_export_star_as = env$1.parse_options.esproposal_export_star_as;
-              var local_name = Curry._2(Parser_env_Peek.value, undefined, env$1) === "as" ? (contextual(env$1, "as"), parse_export_star_as ? Curry._2(Parse.identifier, undefined, env$1) : (error(env$1, /* UnexpectedTypeDeclaration */7), undefined)) : undefined;
-              var specifiers = {
-                TAG: /* ExportBatchSpecifier */1,
-                _0: loc,
-                _1: local_name
-              };
-              var source$1 = export_source(env$1);
-              var loc$1 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
-              var end_loc$2 = loc$1 !== undefined ? loc$1 : source$1[0];
-              var source$2 = source$1;
-              semicolon(env$1);
-              return [
-                      btwn(start_loc, end_loc$2),
-                      {
-                        TAG: /* ExportDeclaration */28,
-                        _0: {
-                          default: false,
-                          declaration: undefined,
-                          specifiers: specifiers,
-                          source: source$2,
-                          exportKind: /* ExportValue */1
-                        }
-                      }
-                    ];
-            }
-          } else {
-            switch (match$1) {
-              case /* T_DEFAULT */34 :
-                  token$4(env$1, /* T_DEFAULT */34);
-                  record_export(env$1, [
-                        btwn(start_loc, Curry._2(Parser_env_Peek.loc, undefined, env$1)),
-                        "default"
-                      ]);
-                  var match$4 = Curry._2(Parser_env_Peek.token, undefined, env$1);
-                  var match$5;
-                  if (match$4 === 13) {
-                    var fn = _function(env$1);
-                    match$5 = [
-                      fn[0],
-                      {
-                        TAG: /* Declaration */0,
-                        _0: fn
-                      }
-                    ];
-                  } else if (Curry._2(Parser_env_Peek.is_class, undefined, env$1)) {
+                if (exit$1 === 3) {
+                  if (Curry._2(Parser_env_Peek.is_class, undefined, env$1)) {
                     var _class = class_declaration(env$1, decorators);
-                    match$5 = [
+                    match$3 = [
                       _class[0],
                       {
                         TAG: /* Declaration */0,
@@ -14249,63 +14110,158 @@ function module_item(env) {
                     ];
                   } else {
                     var expr = Curry._1(Parse.assignment, env$1);
-                    var loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
-                    var end_loc$3 = loc$2 !== undefined ? loc$2 : expr[0];
+                    var loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
+                    var end_loc = loc !== undefined ? loc : expr[0];
                     semicolon(env$1);
-                    match$5 = [
-                      end_loc$3,
+                    match$3 = [
+                      end_loc,
                       {
                         TAG: /* Expression */1,
                         _0: expr
                       }
                     ];
                   }
+                }
+                return [
+                        btwn(start_loc, match$3[0]),
+                        {
+                          TAG: /* ExportDeclaration */28,
+                          _0: {
+                            default: true,
+                            declaration: match$3[1],
+                            specifiers: undefined,
+                            source: undefined,
+                            exportKind: /* ExportValue */1
+                          }
+                        }
+                      ];
+            case /* T_INTERFACE */51 :
+                if (!env$1.parse_options.types) {
+                  error(env$1, /* UnexpectedTypeExport */9);
+                }
+                var $$interface$1 = $$interface(env$1);
+                var match$4 = $$interface$1[1];
+                if (/* tag */typeof match$4 === "number") {
+                  throw {
+                        RE_EXN_ID: "Failure",
+                        _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
+                        Error: new Error()
+                      };
+                }
+                if (match$4.TAG === /* InterfaceDeclaration */21) {
+                  record_export(env$1, [
+                        $$interface$1[0],
+                        extract_ident_name(match$4._0.id)
+                      ]);
+                } else {
+                  throw {
+                        RE_EXN_ID: "Failure",
+                        _1: "Internal Flow Error! Parsed `export interface` into something other than an interface declaration!",
+                        Error: new Error()
+                      };
+                }
+                var end_loc$1 = $$interface$1[0];
+                return [
+                        btwn(start_loc, end_loc$1),
+                        {
+                          TAG: /* ExportDeclaration */28,
+                          _0: {
+                            default: false,
+                            declaration: {
+                              TAG: /* Declaration */0,
+                              _0: $$interface$1
+                            },
+                            specifiers: undefined,
+                            source: undefined,
+                            exportKind: /* ExportType */0
+                          }
+                        }
+                      ];
+            case /* T_TYPE */59 :
+                if (Curry._2(Parser_env_Peek.token, 1, env$1) !== /* T_LCURLY */1) {
+                  if (!env$1.parse_options.types) {
+                    error(env$1, /* UnexpectedTypeExport */9);
+                  }
+                  var type_alias$1 = type_alias(env$1);
+                  var match$5 = type_alias$1[1];
+                  if (/* tag */typeof match$5 === "number") {
+                    throw {
+                          RE_EXN_ID: "Failure",
+                          _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
+                          Error: new Error()
+                        };
+                  }
+                  if (match$5.TAG === /* TypeAlias */7) {
+                    record_export(env$1, [
+                          type_alias$1[0],
+                          extract_ident_name(match$5._0.id)
+                        ]);
+                  } else {
+                    throw {
+                          RE_EXN_ID: "Failure",
+                          _1: "Internal Flow Error! Parsed `export type` into something other than a type alias!",
+                          Error: new Error()
+                        };
+                  }
+                  var end_loc$2 = type_alias$1[0];
                   return [
-                          btwn(start_loc, match$5[0]),
+                          btwn(start_loc, end_loc$2),
                           {
                             TAG: /* ExportDeclaration */28,
                             _0: {
-                              default: true,
-                              declaration: match$5[1],
+                              default: false,
+                              declaration: {
+                                TAG: /* Declaration */0,
+                                _0: type_alias$1
+                              },
                               specifiers: undefined,
                               source: undefined,
-                              exportKind: /* ExportValue */1
+                              exportKind: /* ExportType */0
                             }
                           }
                         ];
-              case /* T_IF */14 :
-              case /* T_IN */15 :
-              case /* T_INSTANCEOF */16 :
-              case /* T_RETURN */17 :
-              case /* T_SWITCH */18 :
-              case /* T_THIS */19 :
-              case /* T_THROW */20 :
-              case /* T_TRY */21 :
-              case /* T_WHILE */23 :
-              case /* T_WITH */24 :
-              case /* T_NULL */27 :
-              case /* T_FALSE */28 :
-              case /* T_TRUE */29 :
-              case /* T_BREAK */30 :
-              case /* T_CASE */31 :
-              case /* T_CATCH */32 :
-              case /* T_CONTINUE */33 :
-              case /* T_DO */35 :
-              case /* T_FINALLY */36 :
-              case /* T_FOR */37 :
-                  exit = 1;
-                  break;
-              case /* T_AT */12 :
-              case /* T_FUNCTION */13 :
-              case /* T_VAR */22 :
-              case /* T_CONST */25 :
-              case /* T_LET */26 :
-              case /* T_CLASS */38 :
-                  exit = 2;
-                  break;
-              default:
+                }
                 exit = 1;
-            }
+                break;
+            case /* T_AT */12 :
+            case /* T_FUNCTION */13 :
+            case /* T_VAR */22 :
+            case /* T_CONST */25 :
+            case /* T_LET */26 :
+            case /* T_CLASS */38 :
+            case /* T_ASYNC */61 :
+                exit = 2;
+                break;
+            case /* T_MULT */97 :
+                var loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env$1);
+                token$4(env$1, /* T_MULT */97);
+                var parse_export_star_as = env$1.parse_options.esproposal_export_star_as;
+                var local_name = Curry._2(Parser_env_Peek.value, undefined, env$1) === "as" ? (contextual(env$1, "as"), parse_export_star_as ? Curry._2(Parse.identifier, undefined, env$1) : (error(env$1, /* UnexpectedTypeDeclaration */7), undefined)) : undefined;
+                var specifiers = {
+                  TAG: /* ExportBatchSpecifier */1,
+                  _0: loc$1,
+                  _1: local_name
+                };
+                var source$1 = export_source(env$1);
+                var loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$1);
+                var end_loc$3 = loc$2 !== undefined ? loc$2 : source$1[0];
+                var source$2 = source$1;
+                semicolon(env$1);
+                return [
+                        btwn(start_loc, end_loc$3),
+                        {
+                          TAG: /* ExportDeclaration */28,
+                          _0: {
+                            default: false,
+                            declaration: undefined,
+                            specifiers: specifiers,
+                            source: source$2,
+                            exportKind: /* ExportValue */1
+                          }
+                        }
+                      ];
+            default:
+              exit = 1;
           }
         } else {
           exit = 1;
@@ -14313,7 +14269,13 @@ function module_item(env) {
         switch (exit) {
           case 1 :
               var match$6 = Curry._2(Parser_env_Peek.token, undefined, env$1);
-              var exportKind = match$6 === 59 ? (token$3(env$1), /* ExportType */0) : /* ExportValue */1;
+              var exportKind;
+              if (/* tag */typeof match$6 === "number" && match$6 === /* T_TYPE */59) {
+                token$3(env$1);
+                exportKind = /* ExportType */0;
+              } else {
+                exportKind = /* ExportValue */1;
+              }
               token$4(env$1, /* T_LCURLY */1);
               var match$7 = export_specifiers_and_errs(env$1, /* [] */0, /* [] */0);
               var specifiers$1 = {
@@ -14348,7 +14310,7 @@ function module_item(env) {
               var match$8 = stmt[1];
               var loc$4 = stmt[0];
               var names;
-              if (typeof match$8 === "number") {
+              if (/* tag */typeof match$8 === "number") {
                 throw {
                       RE_EXN_ID: "Failure",
                       _1: "Internal Flow Error! Unexpected export statement declaration!",
@@ -14437,34 +14399,51 @@ function module_item(env) {
         var start_loc$1 = Curry._2(Parser_env_Peek.loc, undefined, env$2);
         token$4(env$2, /* T_IMPORT */48);
         var match$9 = Curry._2(Parser_env_Peek.token, undefined, env$2);
-        var match$10 = typeof match$9 === "number" ? (
-            match$9 !== 44 ? (
-                match$9 !== 59 ? [
-                    /* ImportValue */2,
-                    undefined
-                  ] : (!env$2.parse_options.types ? error(env$2, /* UnexpectedTypeImport */8) : undefined, [
-                      /* ImportType */0,
-                      Curry._2(Parse.identifier, undefined, env$2)
-                    ])
-              ) : (!env$2.parse_options.types ? error(env$2, /* UnexpectedTypeImport */8) : undefined, token$4(env$2, /* T_TYPEOF */44), [
+        var match$10;
+        if (/* tag */typeof match$9 === "number") {
+          switch (match$9) {
+            case /* T_TYPEOF */44 :
+                if (!env$2.parse_options.types) {
+                  error(env$2, /* UnexpectedTypeImport */8);
+                }
+                token$4(env$2, /* T_TYPEOF */44);
+                match$10 = [
                   /* ImportTypeof */1,
                   undefined
-                ])
-          ) : [
+                ];
+                break;
+            case /* T_TYPE */59 :
+                if (!env$2.parse_options.types) {
+                  error(env$2, /* UnexpectedTypeImport */8);
+                }
+                match$10 = [
+                  /* ImportType */0,
+                  Curry._2(Parse.identifier, undefined, env$2)
+                ];
+                break;
+            default:
+              match$10 = [
+                /* ImportValue */2,
+                undefined
+              ];
+          }
+        } else {
+          match$10 = [
             /* ImportValue */2,
             undefined
           ];
+        }
         var type_ident = match$10[1];
         var importKind = match$10[0];
         var match$11 = Curry._2(Parser_env_Peek.token, undefined, env$2);
         var match$12 = Curry._2(Parser_env_Peek.is_identifier, undefined, env$2);
-        var exit$1 = 0;
         var exit$2 = 0;
-        if (typeof match$11 === "number") {
+        var exit$3 = 0;
+        if (/* tag */typeof match$11 === "number") {
           if (match$11 === /* T_COMMA */8) {
-            exit$1 = 1;
+            exit$2 = 1;
           } else {
-            exit$2 = 2;
+            exit$3 = 2;
           }
         } else if (match$11.TAG === /* T_STRING */1) {
           if (importKind === /* ImportValue */2) {
@@ -14512,13 +14491,13 @@ function module_item(env) {
                     }
                   ];
           }
-          exit$2 = 2;
+          exit$3 = 2;
         } else {
-          exit$2 = 2;
+          exit$3 = 2;
         }
-        if (exit$2 === 2) {
+        if (exit$3 === 2) {
           if (match$12) {
-            exit$1 = 1;
+            exit$2 = 1;
           } else {
             var specifiers$2 = named_or_namespace_specifier(env$2);
             var source$5 = source(env$2);
@@ -14538,23 +14517,42 @@ function module_item(env) {
                   ];
           }
         }
-        if (exit$1 === 1) {
+        if (exit$2 === 1) {
           var match$14 = Curry._2(Parser_env_Peek.token, undefined, env$2);
           var match$15 = Curry._2(Parser_env_Peek.value, undefined, env$2);
           var match$16;
-          var exit$3 = 0;
-          if (type_ident !== undefined && typeof match$14 === "number" && !(match$14 !== 8 && (match$14 !== 0 || match$15 !== "from"))) {
-            match$16 = [
-              /* ImportValue */2,
-              {
-                TAG: /* ImportDefaultSpecifier */1,
-                _0: type_ident
-              }
-            ];
+          var exit$4 = 0;
+          if (type_ident !== undefined && /* tag */typeof match$14 === "number") {
+            switch (match$14) {
+              case /* T_IDENTIFIER */0 :
+                  if (match$15 === "from") {
+                    match$16 = [
+                      /* ImportValue */2,
+                      {
+                        TAG: /* ImportDefaultSpecifier */1,
+                        _0: type_ident
+                      }
+                    ];
+                  } else {
+                    exit$4 = 2;
+                  }
+                  break;
+              case /* T_COMMA */8 :
+                  match$16 = [
+                    /* ImportValue */2,
+                    {
+                      TAG: /* ImportDefaultSpecifier */1,
+                      _0: type_ident
+                    }
+                  ];
+                  break;
+              default:
+                exit$4 = 2;
+            }
           } else {
-            exit$3 = 2;
+            exit$4 = 2;
           }
-          if (exit$3 === 2) {
+          if (exit$4 === 2) {
             match$16 = [
               importKind,
               {
@@ -14564,7 +14562,13 @@ function module_item(env) {
             ];
           }
           var match$17 = Curry._2(Parser_env_Peek.token, undefined, env$2);
-          var additional_specifiers = match$17 === 8 ? (token$4(env$2, /* T_COMMA */8), named_or_namespace_specifier(env$2)) : /* [] */0;
+          var additional_specifiers;
+          if (/* tag */typeof match$17 === "number" && match$17 === /* T_COMMA */8) {
+            token$4(env$2, /* T_COMMA */8);
+            additional_specifiers = named_or_namespace_specifier(env$2);
+          } else {
+            additional_specifiers = /* [] */0;
+          }
           var source$6 = source(env$2);
           var loc$7 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env$2);
           var end_loc$8 = loc$7 !== undefined ? loc$7 : source$6[0];
@@ -14584,17 +14588,7 @@ function module_item(env) {
                   }
                 ];
         }
-        case /* T_SUPER */49 :
-    case /* T_IMPLEMENTS */50 :
-    case /* T_INTERFACE */51 :
-    case /* T_PACKAGE */52 :
-    case /* T_PRIVATE */53 :
-    case /* T_PROTECTED */54 :
-    case /* T_PUBLIC */55 :
-    case /* T_YIELD */56 :
-    case /* T_DEBUGGER */57 :
-        return statement_list_item(decorators, env);
-    case /* T_DECLARE */58 :
+        case /* T_DECLARE */58 :
         if (Curry._2(Parser_env_Peek.token, 1, env) === /* T_EXPORT */47) {
           error_on_decorators(env)(decorators);
           return declare_export_declaration(undefined, env);
@@ -14612,62 +14606,63 @@ function statement_list_item(decoratorsOpt, env) {
     error_on_decorators(env)(decorators);
   }
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (typeof match === "number") {
-    if (match === 25) {
-      return var_or_const(env);
-    }
-    if (match === 26) {
-      var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
-      token$4(env, /* T_LET */26);
-      if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_LPAREN */3) {
-        token$4(env, /* T_LPAREN */3);
-        var match$1 = helper(with_no_let(true, env), /* [] */0, /* [] */0);
-        var head = List.map((function (param) {
-                var match = param[1];
-                return {
-                        id: match.id,
-                        init: match.init
-                      };
-              }), match$1[1]);
-        token$4(env, /* T_RPAREN */4);
-        var body = Curry._1(Parse.statement, env);
-        var end_loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-        var end_loc$1 = end_loc !== undefined ? end_loc : match$1[0];
-        semicolon(env);
-        List.iter((function (param) {
-                return error_at(env, param);
-              }), match$1[2]);
-        return [
-                btwn(start_loc, end_loc$1),
-                {
-                  TAG: /* Let */17,
-                  _0: {
-                    head: head,
-                    body: body
-                  }
-                }
-              ];
-      }
-      var match$2 = helper(with_no_let(true, env), /* [] */0, /* [] */0);
-      var declaration = {
-        TAG: /* VariableDeclaration */19,
-        _0: {
-          declarations: match$2[1],
-          kind: /* Let */1
-        }
-      };
-      var end_loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
-      var end_loc$3 = end_loc$2 !== undefined ? end_loc$2 : match$2[0];
-      semicolon(env);
-      List.iter((function (param) {
-              return error_at(env, param);
-            }), match$2[2]);
-      return [
-              btwn(start_loc, end_loc$3),
-              declaration
-            ];
+  if (/* tag */typeof match === "number") {
+    switch (match) {
+      case /* T_CONST */25 :
+          return var_or_const(env);
+      case /* T_LET */26 :
+          var start_loc = Curry._2(Parser_env_Peek.loc, undefined, env);
+          token$4(env, /* T_LET */26);
+          if (Curry._2(Parser_env_Peek.token, undefined, env) === /* T_LPAREN */3) {
+            token$4(env, /* T_LPAREN */3);
+            var match$1 = helper(with_no_let(true, env), /* [] */0, /* [] */0);
+            var head = List.map((function (param) {
+                    var match = param[1];
+                    return {
+                            id: match.id,
+                            init: match.init
+                          };
+                  }), match$1[1]);
+            token$4(env, /* T_RPAREN */4);
+            var body = Curry._1(Parse.statement, env);
+            var end_loc = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+            var end_loc$1 = end_loc !== undefined ? end_loc : match$1[0];
+            semicolon(env);
+            List.iter((function (param) {
+                    return error_at(env, param);
+                  }), match$1[2]);
+            return [
+                    btwn(start_loc, end_loc$1),
+                    {
+                      TAG: /* Let */17,
+                      _0: {
+                        head: head,
+                        body: body
+                      }
+                    }
+                  ];
+          }
+          var match$2 = helper(with_no_let(true, env), /* [] */0, /* [] */0);
+          var declaration = {
+            TAG: /* VariableDeclaration */19,
+            _0: {
+              declarations: match$2[1],
+              kind: /* Let */1
+            }
+          };
+          var end_loc$2 = Curry._2(Parser_env_Peek.semicolon_loc, undefined, env);
+          var end_loc$3 = end_loc$2 !== undefined ? end_loc$2 : match$2[0];
+          semicolon(env);
+          List.iter((function (param) {
+                  return error_at(env, param);
+                }), match$2[2]);
+          return [
+                  btwn(start_loc, end_loc$3),
+                  declaration
+                ];
+      default:
+        
     }
-    
   }
   if (Curry._2(Parser_env_Peek.is_function, undefined, env)) {
     return _function(env);
@@ -14675,19 +14670,12 @@ function statement_list_item(decoratorsOpt, env) {
   if (Curry._2(Parser_env_Peek.is_class, undefined, env)) {
     return class_declaration$1(env, decorators);
   }
-  if (typeof match !== "number") {
+  if (/* tag */typeof match !== "number") {
     return statement(env);
   }
   switch (match) {
     case /* T_INTERFACE */51 :
         return $$interface(env);
-    case /* T_PACKAGE */52 :
-    case /* T_PRIVATE */53 :
-    case /* T_PROTECTED */54 :
-    case /* T_PUBLIC */55 :
-    case /* T_YIELD */56 :
-    case /* T_DEBUGGER */57 :
-        return statement(env);
     case /* T_DECLARE */58 :
         return declare(undefined, env);
     case /* T_TYPE */59 :
@@ -14706,7 +14694,7 @@ function statement_list(_env, term_fn, item_fn, _param) {
     var stmts = param[1];
     var string_tokens = param[0];
     var t = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (t === 105) {
+    if (/* tag */typeof t === "number" && t === /* T_EOF */105) {
       return [
               env,
               string_tokens,
@@ -14732,7 +14720,7 @@ function statement_list(_env, term_fn, item_fn, _param) {
       tl: stmts
     };
     var match = possible_directive[1];
-    if (typeof match === "number") {
+    if (/* tag */typeof match === "number") {
       return [
               env,
               string_tokens,
@@ -14748,7 +14736,7 @@ function statement_list(_env, term_fn, item_fn, _param) {
     }
     var match$1 = match._0.expression;
     var match$2 = match$1[1];
-    if (typeof match$2 === "number") {
+    if (/* tag */typeof match$2 === "number") {
       return [
               env,
               string_tokens,
@@ -14763,7 +14751,7 @@ function statement_list(_env, term_fn, item_fn, _param) {
             ];
     }
     var str = match$2._0.value;
-    if (typeof str === "number") {
+    if (/* tag */typeof str === "number") {
       return [
               env,
               string_tokens,
@@ -14801,7 +14789,7 @@ function directives(env, term_fn, item_fn) {
   var env$1 = match[0];
   List.iter((function (param) {
           var token = param[1];
-          if (typeof token !== "number" && token.TAG === /* T_STRING */1) {
+          if (/* tag */typeof token !== "number" && token.TAG === /* T_STRING */1) {
             if (token._0[3]) {
               return strict_error_at(env$1, [
                           param[0],
@@ -14829,7 +14817,7 @@ function module_body(term_fn, env) {
   while(true) {
     var acc = _acc;
     var t = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (t === 105) {
+    if (/* tag */typeof t === "number" && t === /* T_EOF */105) {
       return List.rev(acc);
     }
     if (Curry._1(term_fn, t)) {
@@ -14848,7 +14836,7 @@ function statement_list$1(term_fn, env) {
   while(true) {
     var acc = _acc;
     var t = Curry._2(Parser_env_Peek.token, undefined, env);
-    if (t === 105) {
+    if (/* tag */typeof t === "number" && t === /* T_EOF */105) {
       return List.rev(acc);
     }
     if (Curry._1(term_fn, t)) {
@@ -14895,7 +14883,8 @@ function identifier$2(restricted_error, env) {
   var loc = Curry._2(Parser_env_Peek.loc, undefined, env);
   var name = Curry._2(Parser_env_Peek.value, undefined, env);
   var t = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (t === 26) {
+  var exit = 0;
+  if (/* tag */typeof t === "number" && t === /* T_LET */26) {
     if (env.in_strict_mode) {
       strict_error(env, /* StrictReservedWord */39);
     } else if (env.no_let) {
@@ -14905,13 +14894,28 @@ function identifier$2(restricted_error, env) {
           });
     }
     token$3(env);
-  } else if (is_strict_reserved(name)) {
-    strict_error(env, /* StrictReservedWord */39);
-    token$3(env);
-  } else if (typeof t === "number" && !(t > 62 || t < 58)) {
-    token$4(env, t);
   } else {
-    token$4(env, /* T_IDENTIFIER */0);
+    exit = 1;
+  }
+  if (exit === 1) {
+    if (is_strict_reserved(name)) {
+      strict_error(env, /* StrictReservedWord */39);
+      token$3(env);
+    } else if (/* tag */typeof t === "number") {
+      switch (t) {
+        case /* T_DECLARE */58 :
+        case /* T_TYPE */59 :
+        case /* T_OF */60 :
+        case /* T_ASYNC */61 :
+        case /* T_AWAIT */62 :
+            token$4(env, t);
+            break;
+        default:
+          token$4(env, /* T_IDENTIFIER */0);
+      }
+    } else {
+      token$4(env, /* T_IDENTIFIER */0);
+    }
   }
   if (restricted_error !== undefined && is_restricted(name)) {
     strict_error_at(env, [
@@ -14947,7 +14951,7 @@ function program(env) {
 function expression$1(env) {
   var expr = Curry._1(assignment, env);
   var match = Curry._2(Parser_env_Peek.token, undefined, env);
-  if (match === 8) {
+  if (/* tag */typeof match === "number" && match === /* T_COMMA */8) {
     return sequence(env, {
                 hd: expr,
                 tl: /* [] */0
@@ -15271,7 +15275,7 @@ function parse(content, options) {
     var loc = function ($$location) {
       var match = $$location.source;
       var source = match !== undefined ? (
-          typeof match === "number" ? string("(global)") : string(match._0)
+          /* tag */typeof match === "number" ? string("(global)") : string(match._0)
         ) : $$null;
       return obj([
                   [
@@ -15328,7 +15332,7 @@ function parse(content, options) {
     var _type = function (param) {
       var t = param[1];
       var loc = param[0];
-      if (typeof t === "number") {
+      if (/* tag */typeof t === "number") {
         switch (t) {
           case /* Any */0 :
               return node("AnyTypeAnnotation", loc, []);
@@ -15558,7 +15562,7 @@ function parse(content, options) {
     var expression = function (param) {
       var arr = param[1];
       var loc = param[0];
-      if (typeof arr === "number") {
+      if (/* tag */typeof arr === "number") {
         return node("ThisExpression", loc, []);
       }
       switch (arr.TAG | 0) {
@@ -15636,7 +15640,7 @@ function parse(content, options) {
         case /* Unary */5 :
             var unary = arr._0;
             var match = unary.operator;
-            if (match >= 7) {
+            if (match === /* Await */7) {
               return node("AwaitExpression", loc, [[
                             "argument",
                             expression(unary.argument)
@@ -16198,7 +16202,7 @@ function parse(content, options) {
     var statement = function (param) {
       var b = param[1];
       var loc = param[0];
-      if (typeof b === "number") {
+      if (/* tag */typeof b === "number") {
         if (b === /* Empty */0) {
           return node("EmptyStatement", loc, []);
         } else {
@@ -16842,7 +16846,7 @@ function parse(content, options) {
       var value = lit.value;
       var loc = param[0];
       var value_;
-      if (typeof value === "number") {
+      if (/* tag */typeof value === "number") {
         value_ = $$null;
       } else {
         switch (value.TAG | 0) {
@@ -16864,7 +16868,7 @@ function parse(content, options) {
       }
       var props;
       var exit = 0;
-      if (typeof value === "number" || value.TAG !== /* RegExp */3) {
+      if (/* tag */typeof value === "number" || value.TAG !== /* RegExp */3) {
         exit = 1;
       } else {
         var match$1 = value._0;
diff --git a/jscomp/test/fun_pattern_match.js b/jscomp/test/fun_pattern_match.js
index be00d13676..fd289f57b7 100644
--- a/jscomp/test/fun_pattern_match.js
+++ b/jscomp/test/fun_pattern_match.js
@@ -15,29 +15,23 @@ function f3(param) {
   var lhs = param.rank;
   return function (param) {
     var rhs = param.rank;
-    if (typeof lhs === "number") {
-      throw {
-            RE_EXN_ID: "Assert_failure",
-            _1: [
-              "fun_pattern_match.ml",
-              44,
-              9
-            ],
-            Error: new Error()
-          };
+    if (/* tag */typeof lhs === "number") {
+      lhs === /* Uninitialized */0;
+    } else {
+      if (/* tag */typeof rhs !== "number") {
+        return Caml.int_compare(lhs._0, rhs._0);
+      }
+      rhs === /* Uninitialized */0;
     }
-    if (typeof rhs === "number") {
-      throw {
-            RE_EXN_ID: "Assert_failure",
-            _1: [
-              "fun_pattern_match.ml",
-              44,
-              9
-            ],
-            Error: new Error()
-          };
-    }
-    return Caml.int_compare(lhs._0, rhs._0);
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "fun_pattern_match.ml",
+            44,
+            9
+          ],
+          Error: new Error()
+        };
   };
 }
 
@@ -45,29 +39,23 @@ function f4(param) {
   var lhs = param.rank;
   return function (param) {
     var rhs = param.rank;
-    if (typeof lhs === "number") {
-      throw {
-            RE_EXN_ID: "Assert_failure",
-            _1: [
-              "fun_pattern_match.ml",
-              52,
-              9
-            ],
-            Error: new Error()
-          };
-    }
-    if (typeof rhs === "number") {
-      throw {
-            RE_EXN_ID: "Assert_failure",
-            _1: [
-              "fun_pattern_match.ml",
-              52,
-              9
-            ],
-            Error: new Error()
-          };
+    if (/* tag */typeof lhs === "number") {
+      lhs === /* Uninitialized */0;
+    } else {
+      if (/* tag */typeof rhs !== "number") {
+        return Caml.int_compare(lhs._0, rhs._0);
+      }
+      rhs === /* Uninitialized */0;
     }
-    return Caml.int_compare(lhs._0, rhs._0);
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "fun_pattern_match.ml",
+            52,
+            9
+          ],
+          Error: new Error()
+        };
   };
 }
 
diff --git a/jscomp/test/gpr_1658_test.js b/jscomp/test/gpr_1658_test.js
index 66b09303d4..a0c151cfef 100644
--- a/jscomp/test/gpr_1658_test.js
+++ b/jscomp/test/gpr_1658_test.js
@@ -32,7 +32,7 @@ eq("File \"gpr_1658_test.ml\", line 11, characters 7-14", null, null);
 
 var match = Js_types.classify(null);
 
-if (match === 2) {
+if (/* tag */typeof match === "number" && match === /* JSNull */2) {
   eq("File \"gpr_1658_test.ml\", line 14, characters 11-18", true, true);
 } else {
   eq("File \"gpr_1658_test.ml\", line 16, characters 11-18", true, false);
diff --git a/jscomp/test/gpr_3209_test.js b/jscomp/test/gpr_3209_test.js
index ccdb340145..fec8f3e920 100644
--- a/jscomp/test/gpr_3209_test.js
+++ b/jscomp/test/gpr_3209_test.js
@@ -2,7 +2,7 @@
 
 
 function f9(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     switch (param) {
       case /* T60 */0 :
       case /* T61 */1 :
diff --git a/jscomp/test/gpr_3609_test.js b/jscomp/test/gpr_3609_test.js
index 410908db55..7cb88b2676 100644
--- a/jscomp/test/gpr_3609_test.js
+++ b/jscomp/test/gpr_3609_test.js
@@ -2,7 +2,7 @@
 
 
 function func(state) {
-  if (typeof state === "number") {
+  if (/* tag */typeof state === "number") {
     return 0;
   } else {
     return 0 + state._0 | 0;
diff --git a/jscomp/test/gpr_4900_test.js b/jscomp/test/gpr_4900_test.js
index 5512ae1a9f..74ae3021a2 100644
--- a/jscomp/test/gpr_4900_test.js
+++ b/jscomp/test/gpr_4900_test.js
@@ -11,16 +11,18 @@ var test_id = {
 };
 
 function showToJs(x) {
-  return x !== 0;
+  if (/* tag */typeof x === "number" && x === /* No */0) {
+    return false;
+  } else {
+    return true;
+  }
 }
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 15, characters 30-37", showToJs(/* Yes */1), true);
+Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 15, characters 30-37", true, true);
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 16, characters 30-37", showToJs(/* No */0), false);
+Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 16, characters 30-37", false, false);
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 17, characters 30-37", showToJs(/* After */{
-          _0: 3
-        }), true);
+Mt.eq_suites(test_id, suites, "File \"gpr_4900_test.ml\", line 17, characters 30-37", true, true);
 
 Mt.from_pair_suites("File \"gpr_4900_test.ml\", line 19, characters 20-27", suites.contents);
 
diff --git a/jscomp/test/gpr_4924_test.js b/jscomp/test/gpr_4924_test.js
index ccd700b381..3ba99c54b6 100644
--- a/jscomp/test/gpr_4924_test.js
+++ b/jscomp/test/gpr_4924_test.js
@@ -11,7 +11,7 @@ var test_id = {
 };
 
 function u(b) {
-  if (b === 0) {
+  if (/* tag */typeof b === "number" && b === /* A */0) {
     return 0;
   } else {
     return 1;
@@ -19,23 +19,29 @@ function u(b) {
 }
 
 function u1(b) {
-  return b === 0;
+  if (/* tag */typeof b === "number" && b === /* A */0) {
+    return true;
+  } else {
+    return false;
+  }
 }
 
 function u2(b) {
-  return b !== 0;
+  if (/* tag */typeof b === "number" && b === /* A */0) {
+    return false;
+  } else {
+    return true;
+  }
 }
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 25, characters 30-37", u2(/* A */0), false);
+Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 25, characters 30-37", false, false);
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 26, characters 30-37", u2(/* B */1), true);
+Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 26, characters 30-37", true, true);
 
-Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 27, characters 30-37", u2(/* C */{
-          _0: 2
-        }), true);
+Mt.eq_suites(test_id, suites, "File \"gpr_4924_test.ml\", line 27, characters 30-37", true, true);
 
 function u3(b) {
-  if (b === 0) {
+  if (/* tag */typeof b === "number" && b === /* A */0) {
     return 3;
   } else {
     return 4;
@@ -43,7 +49,7 @@ function u3(b) {
 }
 
 function u4(b) {
-  if (b === 0) {
+  if (/* tag */typeof b === "number" && b === /* A */0) {
     return 3;
   } else {
     return 4;
@@ -51,11 +57,19 @@ function u4(b) {
 }
 
 function u5(b) {
-  return b !== 0;
+  if (/* tag */typeof b === "number" && b === /* A */0) {
+    return false;
+  } else {
+    return true;
+  }
 }
 
 function u6(b) {
-  return b === 0;
+  if (/* tag */typeof b === "number" && b === /* A */0) {
+    return true;
+  } else {
+    return false;
+  }
 }
 
 Mt.from_pair_suites("File \"gpr_4924_test.ml\", line 49, characters 20-27", suites.contents);
diff --git a/jscomp/test/gpr_5280_optimize_test.js b/jscomp/test/gpr_5280_optimize_test.js
index 77e3062ad2..bfe97c2249 100644
--- a/jscomp/test/gpr_5280_optimize_test.js
+++ b/jscomp/test/gpr_5280_optimize_test.js
@@ -5,8 +5,10 @@ var a = /* Color */{
   _0: "#ffff"
 };
 
-var c = "white";
+var c;
+
+c = /* tag */typeof a === "number" ? "orange" : "white";
 
 exports.a = a;
 exports.c = c;
-/* No side effect */
+/* c Not a pure module */
diff --git a/jscomp/test/inline_map2_test.js b/jscomp/test/inline_map2_test.js
index d6d3320072..e750e8824b 100644
--- a/jscomp/test/inline_map2_test.js
+++ b/jscomp/test/inline_map2_test.js
@@ -8,10 +8,10 @@ var Caml_option = require("../../lib/js/caml_option.js");
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param._4;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param._4;
     }
   };
   var create = function (l, x, d, r) {
@@ -35,26 +35,28 @@ function Make(Ord) {
           };
   };
   var bal = function (l, x, d, r) {
-    var hl = l ? l._4 : 0;
-    var hr = r ? r._4 : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l._4;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r._4;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l._3;
-        var ld = l._2;
-        var lv = l._1;
-        var ll = l._0;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, ld, create(lr, x, d, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
               Error: new Error()
             };
       }
+      var lr = l._3;
+      var ld = l._2;
+      var lv = l._1;
+      var ll = l._0;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, ld, create(lr, x, d, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
@@ -70,23 +72,23 @@ function Make(Ord) {
               _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r._3;
-      var rd = r._2;
-      var rv = r._1;
-      var rl = r._0;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, x, d, rl), rv, rd, rr);
-      }
-      if (rl) {
-        return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var rr = r._3;
+    var rd = r._2;
+    var rv = r._1;
+    var rl = r._0;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, x, d, rl), rv, rd, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -94,14 +96,14 @@ function Make(Ord) {
         };
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var add = function (x, data, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Node */{
               _0: /* Empty */0,
               _1: x,
@@ -132,24 +134,24 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var c = Curry._2(Ord.compare, x, param._1);
-        if (c === 0) {
-          return param._2;
-        }
-        _param = c < 0 ? param._0 : param._3;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = Curry._2(Ord.compare, x, param._1);
+      if (c === 0) {
+        return param._2;
+      }
+      _param = c < 0 ? param._0 : param._3;
+      continue ;
     };
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param._1);
@@ -163,60 +165,60 @@ function Make(Ord) {
   var min_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param._0;
-        if (!l) {
-          return [
-                  param._1,
-                  param._2
-                ];
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param._0;
+      if (/* tag */typeof l === "number") {
+        return [
+                param._1,
+                param._2
+              ];
+      }
+      _param = l;
+      continue ;
     };
   };
   var max_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param._3;
-        if (!r) {
-          return [
-                  param._1,
-                  param._2
-                ];
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param._3;
+      if (/* tag */typeof r === "number") {
+        return [
+                param._1,
+                param._2
+              ];
+      }
+      _param = r;
+      continue ;
     };
   };
   var remove_min_binding = function (param) {
-    if (param) {
-      var l = param._0;
-      if (l) {
-        return bal(remove_min_binding(l), param._1, param._2, param._3);
-      } else {
-        return param._3;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Map.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param._0;
+    if (/* tag */typeof l === "number") {
+      return param._3;
+    } else {
+      return bal(remove_min_binding(l), param._1, param._2, param._3);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
   };
   var remove = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var r = param._3;
@@ -225,10 +227,10 @@ function Make(Ord) {
     var l = param._0;
     var c = Curry._2(Ord.compare, x, v);
     if (c === 0) {
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return r;
       }
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return l;
       }
       var match = min_binding(r);
@@ -242,7 +244,7 @@ function Make(Ord) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param._0);
@@ -252,7 +254,7 @@ function Make(Ord) {
     };
   };
   var map = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var l$p = map(f, param._0);
@@ -267,7 +269,7 @@ function Make(Ord) {
           };
   };
   var mapi = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param._1;
@@ -286,7 +288,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return accu;
       }
       _accu = Curry._3(f, m._1, m._2, fold(f, m._0, accu));
@@ -297,7 +299,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._2(p, param._1, param._2)) {
@@ -313,7 +315,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._2(p, param._1, param._2)) {
@@ -327,28 +329,28 @@ function Make(Ord) {
     };
   };
   var add_min_binding = function (k, v, param) {
-    if (param) {
-      return bal(add_min_binding(k, v, param._0), param._1, param._2, param._3);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, v);
+    } else {
+      return bal(add_min_binding(k, v, param._0), param._1, param._2, param._3);
     }
   };
   var add_max_binding = function (k, v, param) {
-    if (param) {
-      return bal(param._0, param._1, param._2, add_max_binding(k, v, param._3));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, v);
+    } else {
+      return bal(param._0, param._1, param._2, add_max_binding(k, v, param._3));
     }
   };
   var join = function (l, v, d, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_binding(v, d, r);
     }
-    if (!r) {
+    var lh = l._4;
+    if (/* tag */typeof r === "number") {
       return add_max_binding(v, d, l);
     }
     var rh = r._4;
-    var lh = l._4;
     if (lh > (rh + 2 | 0)) {
       return bal(l._0, l._1, l._2, join(l._3, v, d, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -358,10 +360,10 @@ function Make(Ord) {
     }
   };
   var concat = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
@@ -375,7 +377,7 @@ function Make(Ord) {
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               undefined,
@@ -410,33 +412,36 @@ function Make(Ord) {
           ];
   };
   var merge = function (f, s1, s2) {
-    if (s1) {
+    if (/* tag */typeof s1 === "number") {
+      if (/* tag */typeof s2 === "number") {
+        return /* Empty */0;
+      }
+      
+    } else {
       var v1 = s1._1;
       if (s1._4 >= height(s2)) {
         var match = split(v1, s2);
         return concat_or_join(merge(f, s1._0, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1._2), match[1]), merge(f, s1._3, match[2]));
       }
       
-    } else if (!s2) {
-      return /* Empty */0;
     }
-    if (s2) {
-      var v2 = s2._1;
-      var match$1 = split(v2, s1);
-      return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
+    if (/* tag */typeof s2 === "number") {
+      throw {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "inline_map2_test.ml",
+              270,
+              10
+            ],
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "inline_map2_test.ml",
-            270,
-            10
-          ],
-          Error: new Error()
-        };
+    var v2 = s2._1;
+    var match$1 = split(v2, s1);
+    return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
   };
   var filter = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var d = param._2;
@@ -451,7 +456,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -482,7 +487,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return e;
       }
       _e = /* More */{
@@ -501,14 +506,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -530,14 +535,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return false;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return true;
+        } else {
+          return false;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return false;
       }
       if (Curry._2(Ord.compare, e1._0, e2._0) !== 0) {
@@ -552,17 +557,17 @@ function Make(Ord) {
     };
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param._0) + 1 | 0) + cardinal(param._3) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param._0) + 1 | 0) + cardinal(param._3) | 0;
     }
   };
   var bindings_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param._0;
@@ -619,10 +624,10 @@ function Make(Ord) {
 }
 
 function height(param) {
-  if (param) {
-    return param._4;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._4;
   }
 }
 
@@ -649,26 +654,28 @@ function singleton(x, d) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l._4 : 0;
-  var hr = r ? r._4 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._4;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._4;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._3;
-      var ld = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l._3;
+    var ld = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -684,23 +691,23 @@ function bal(l, x, d, r) {
             _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._3;
-    var rd = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r._3;
+  var rd = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -709,15 +716,15 @@ function bal(l, x, d, r) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function add(x, data, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -749,25 +756,25 @@ function add(x, data, param) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.int_compare(x, param._1);
-      if (c === 0) {
-        return param._2;
-      }
-      _param = c < 0 ? param._0 : param._3;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(x, param._1);
+    if (c === 0) {
+      return param._2;
+    }
+    _param = c < 0 ? param._0 : param._3;
+    continue ;
   };
 }
 
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.int_compare(x, param._1);
@@ -782,63 +789,63 @@ function mem(x, _param) {
 function min_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param._0;
-      if (!l) {
-        return [
-                param._1,
-                param._2
-              ];
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param._0;
+    if (/* tag */typeof l === "number") {
+      return [
+              param._1,
+              param._2
+            ];
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function max_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param._3;
-      if (!r) {
-        return [
-                param._1,
-                param._2
-              ];
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param._3;
+    if (/* tag */typeof r === "number") {
+      return [
+              param._1,
+              param._2
+            ];
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function remove_min_binding(param) {
-  if (param) {
-    var l = param._0;
-    if (l) {
-      return bal(remove_min_binding(l), param._1, param._2, param._3);
-    } else {
-      return param._3;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Map.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param._0;
+  if (/* tag */typeof l === "number") {
+    return param._3;
+  } else {
+    return bal(remove_min_binding(l), param._1, param._2, param._3);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function remove(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var r = param._3;
@@ -847,10 +854,10 @@ function remove(x, param) {
   var l = param._0;
   var c = Caml.int_compare(x, v);
   if (c === 0) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return r;
     }
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return l;
     }
     var match = min_binding(r);
@@ -865,7 +872,7 @@ function remove(x, param) {
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param._0);
@@ -876,7 +883,7 @@ function iter(f, _param) {
 }
 
 function map(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var l$p = map(f, param._0);
@@ -892,7 +899,7 @@ function map(f, param) {
 }
 
 function mapi(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param._1;
@@ -912,7 +919,7 @@ function fold(f, _m, _accu) {
   while(true) {
     var accu = _accu;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return accu;
     }
     _accu = Curry._3(f, m._1, m._2, fold(f, m._0, accu));
@@ -924,7 +931,7 @@ function fold(f, _m, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._2(p, param._1, param._2)) {
@@ -941,7 +948,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._2(p, param._1, param._2)) {
@@ -956,30 +963,30 @@ function exists(p, _param) {
 }
 
 function add_min_binding(k, v, param) {
-  if (param) {
-    return bal(add_min_binding(k, v, param._0), param._1, param._2, param._3);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, v);
+  } else {
+    return bal(add_min_binding(k, v, param._0), param._1, param._2, param._3);
   }
 }
 
 function add_max_binding(k, v, param) {
-  if (param) {
-    return bal(param._0, param._1, param._2, add_max_binding(k, v, param._3));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, v);
+  } else {
+    return bal(param._0, param._1, param._2, add_max_binding(k, v, param._3));
   }
 }
 
 function join(l, v, d, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_binding(v, d, r);
   }
-  if (!r) {
+  var lh = l._4;
+  if (/* tag */typeof r === "number") {
     return add_max_binding(v, d, l);
   }
   var rh = r._4;
-  var lh = l._4;
   if (lh > (rh + 2 | 0)) {
     return bal(l._0, l._1, l._2, join(l._3, v, d, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -990,10 +997,10 @@ function join(l, v, d, r) {
 }
 
 function concat(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -1009,7 +1016,7 @@ function concat_or_join(t1, v, d, t2) {
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             undefined,
@@ -1045,34 +1052,37 @@ function split(x, param) {
 }
 
 function merge(f, s1, s2) {
-  if (s1) {
+  if (/* tag */typeof s1 === "number") {
+    if (/* tag */typeof s2 === "number") {
+      return /* Empty */0;
+    }
+    
+  } else {
     var v1 = s1._1;
     if (s1._4 >= height(s2)) {
       var match = split(v1, s2);
       return concat_or_join(merge(f, s1._0, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1._2), match[1]), merge(f, s1._3, match[2]));
     }
     
-  } else if (!s2) {
-    return /* Empty */0;
   }
-  if (s2) {
-    var v2 = s2._1;
-    var match$1 = split(v2, s1);
-    return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
+  if (/* tag */typeof s2 === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "inline_map2_test.ml",
+            270,
+            10
+          ],
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "inline_map2_test.ml",
-          270,
-          10
-        ],
-        Error: new Error()
-      };
+  var v2 = s2._1;
+  var match$1 = split(v2, s1);
+  return concat_or_join(merge(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge(f, match$1[2], s2._3));
 }
 
 function filter(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var d = param._2;
@@ -1088,7 +1098,7 @@ function filter(p, param) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -1120,7 +1130,7 @@ function cons_enum(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -1140,14 +1150,14 @@ function compare(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.int_compare(e1._0, e2._0);
@@ -1170,14 +1180,14 @@ function equal(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (e1._0 !== e2._0) {
@@ -1193,10 +1203,10 @@ function equal(cmp, m1, m2) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param._0) + 1 | 0) + cardinal(param._3) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param._0) + 1 | 0) + cardinal(param._3) | 0;
   }
 }
 
@@ -1204,7 +1214,7 @@ function bindings_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param._0;
@@ -1290,10 +1300,10 @@ var m = List.fold_left((function (acc, param) {
     });
 
 function height$1(param) {
-  if (param) {
-    return param._4;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._4;
   }
 }
 
@@ -1320,26 +1330,28 @@ function singleton$1(x, d) {
 }
 
 function bal$1(l, x, d, r) {
-  var hl = l ? l._4 : 0;
-  var hr = r ? r._4 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._4;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._4;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._3;
-      var ld = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height$1(ll) >= height$1(lr)) {
-        return create$1(ll, lv, ld, create$1(lr, x, d, r));
-      }
-      if (lr) {
-        return create$1(create$1(ll, lv, ld, lr._0), lr._1, lr._2, create$1(lr._3, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l._3;
+    var ld = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height$1(ll) >= height$1(lr)) {
+      return create$1(ll, lv, ld, create$1(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$1(create$1(ll, lv, ld, lr._0), lr._1, lr._2, create$1(lr._3, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -1355,23 +1367,23 @@ function bal$1(l, x, d, r) {
             _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._3;
-    var rd = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height$1(rr) >= height$1(rl)) {
-      return create$1(create$1(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create$1(create$1(l, x, d, rl._0), rl._1, rl._2, create$1(rl._3, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r._3;
+  var rd = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height$1(rr) >= height$1(rl)) {
+    return create$1(create$1(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$1(create$1(l, x, d, rl._0), rl._1, rl._2, create$1(rl._3, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -1380,15 +1392,15 @@ function bal$1(l, x, d, r) {
 }
 
 function is_empty$1(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function add$1(x, data, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -1420,25 +1432,25 @@ function add$1(x, data, param) {
 function find$1(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.string_compare(x, param._1);
-      if (c === 0) {
-        return param._2;
-      }
-      _param = c < 0 ? param._0 : param._3;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.string_compare(x, param._1);
+    if (c === 0) {
+      return param._2;
+    }
+    _param = c < 0 ? param._0 : param._3;
+    continue ;
   };
 }
 
 function mem$1(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.string_compare(x, param._1);
@@ -1453,63 +1465,63 @@ function mem$1(x, _param) {
 function min_binding$1(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param._0;
-      if (!l) {
-        return [
-                param._1,
-                param._2
-              ];
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param._0;
+    if (/* tag */typeof l === "number") {
+      return [
+              param._1,
+              param._2
+            ];
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function max_binding$1(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param._3;
-      if (!r) {
-        return [
-                param._1,
-                param._2
-              ];
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param._3;
+    if (/* tag */typeof r === "number") {
+      return [
+              param._1,
+              param._2
+            ];
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function remove_min_binding$1(param) {
-  if (param) {
-    var l = param._0;
-    if (l) {
-      return bal$1(remove_min_binding$1(l), param._1, param._2, param._3);
-    } else {
-      return param._3;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Map.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param._0;
+  if (/* tag */typeof l === "number") {
+    return param._3;
+  } else {
+    return bal$1(remove_min_binding$1(l), param._1, param._2, param._3);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function remove$1(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var r = param._3;
@@ -1518,10 +1530,10 @@ function remove$1(x, param) {
   var l = param._0;
   var c = Caml.string_compare(x, v);
   if (c === 0) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return r;
     }
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return l;
     }
     var match = min_binding$1(r);
@@ -1536,7 +1548,7 @@ function remove$1(x, param) {
 function iter$1(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter$1(f, param._0);
@@ -1547,7 +1559,7 @@ function iter$1(f, _param) {
 }
 
 function map$1(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var l$p = map$1(f, param._0);
@@ -1563,7 +1575,7 @@ function map$1(f, param) {
 }
 
 function mapi$1(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param._1;
@@ -1583,7 +1595,7 @@ function fold$1(f, _m, _accu) {
   while(true) {
     var accu = _accu;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return accu;
     }
     _accu = Curry._3(f, m._1, m._2, fold$1(f, m._0, accu));
@@ -1595,7 +1607,7 @@ function fold$1(f, _m, _accu) {
 function for_all$1(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._2(p, param._1, param._2)) {
@@ -1612,7 +1624,7 @@ function for_all$1(p, _param) {
 function exists$1(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._2(p, param._1, param._2)) {
@@ -1627,30 +1639,30 @@ function exists$1(p, _param) {
 }
 
 function add_min_binding$1(k, v, param) {
-  if (param) {
-    return bal$1(add_min_binding$1(k, v, param._0), param._1, param._2, param._3);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton$1(k, v);
+  } else {
+    return bal$1(add_min_binding$1(k, v, param._0), param._1, param._2, param._3);
   }
 }
 
 function add_max_binding$1(k, v, param) {
-  if (param) {
-    return bal$1(param._0, param._1, param._2, add_max_binding$1(k, v, param._3));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton$1(k, v);
+  } else {
+    return bal$1(param._0, param._1, param._2, add_max_binding$1(k, v, param._3));
   }
 }
 
 function join$1(l, v, d, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_binding$1(v, d, r);
   }
-  if (!r) {
+  var lh = l._4;
+  if (/* tag */typeof r === "number") {
     return add_max_binding$1(v, d, l);
   }
   var rh = r._4;
-  var lh = l._4;
   if (lh > (rh + 2 | 0)) {
     return bal$1(l._0, l._1, l._2, join$1(l._3, v, d, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -1661,10 +1673,10 @@ function join$1(l, v, d, r) {
 }
 
 function concat$1(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding$1(t2);
@@ -1680,7 +1692,7 @@ function concat_or_join$1(t1, v, d, t2) {
 }
 
 function split$1(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             undefined,
@@ -1716,34 +1728,37 @@ function split$1(x, param) {
 }
 
 function merge$1(f, s1, s2) {
-  if (s1) {
+  if (/* tag */typeof s1 === "number") {
+    if (/* tag */typeof s2 === "number") {
+      return /* Empty */0;
+    }
+    
+  } else {
     var v1 = s1._1;
     if (s1._4 >= height$1(s2)) {
       var match = split$1(v1, s2);
       return concat_or_join$1(merge$1(f, s1._0, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1._2), match[1]), merge$1(f, s1._3, match[2]));
     }
     
-  } else if (!s2) {
-    return /* Empty */0;
   }
-  if (s2) {
-    var v2 = s2._1;
-    var match$1 = split$1(v2, s1);
-    return concat_or_join$1(merge$1(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge$1(f, match$1[2], s2._3));
+  if (/* tag */typeof s2 === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "inline_map2_test.ml",
+            270,
+            10
+          ],
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "inline_map2_test.ml",
-          270,
-          10
-        ],
-        Error: new Error()
-      };
+  var v2 = s2._1;
+  var match$1 = split$1(v2, s1);
+  return concat_or_join$1(merge$1(f, match$1[0], s2._0), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2._2)), merge$1(f, match$1[2], s2._3));
 }
 
 function filter$1(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var d = param._2;
@@ -1759,7 +1774,7 @@ function filter$1(p, param) {
 }
 
 function partition$1(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -1791,7 +1806,7 @@ function cons_enum$1(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -1811,14 +1826,14 @@ function compare$1(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.string_compare(e1._0, e2._0);
@@ -1841,14 +1856,14 @@ function equal$1(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (Caml.string_compare(e1._0, e2._0) !== 0) {
@@ -1864,10 +1879,10 @@ function equal$1(cmp, m1, m2) {
 }
 
 function cardinal$1(param) {
-  if (param) {
-    return (cardinal$1(param._0) + 1 | 0) + cardinal$1(param._3) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal$1(param._0) + 1 | 0) + cardinal$1(param._3) | 0;
   }
 }
 
@@ -1875,7 +1890,7 @@ function bindings_aux$1(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param._0;
diff --git a/jscomp/test/inline_map_demo.js b/jscomp/test/inline_map_demo.js
index 2846e9c70e..c141f7d250 100644
--- a/jscomp/test/inline_map_demo.js
+++ b/jscomp/test/inline_map_demo.js
@@ -5,10 +5,10 @@ var Caml = require("../../lib/js/caml.js");
 var List = require("../../lib/js/list.js");
 
 function height(x) {
-  if (x) {
-    return x._4;
-  } else {
+  if (/* tag */typeof x === "number") {
     return 0;
+  } else {
+    return x._4;
   }
 }
 
@@ -25,36 +25,38 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l._4 : 0;
-  var hr = r ? r._4 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._4;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._4;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._3;
-      var ld = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Assert_failure",
             _1: [
               "inline_map_demo.res",
-              47,
-              19
+              41,
+              15
             ],
             Error: new Error()
           };
     }
+    var lr = l._3;
+    var ld = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
             "inline_map_demo.res",
-            41,
-            15
+            47,
+            19
           ],
           Error: new Error()
         };
@@ -68,40 +70,40 @@ function bal(l, x, d, r) {
             _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._3;
-    var rd = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
             "inline_map_demo.res",
-            61,
-            19
+            55,
+            15
           ],
           Error: new Error()
         };
   }
+  var rr = r._3;
+  var rd = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Assert_failure",
         _1: [
           "inline_map_demo.res",
-          55,
-          15
+          61,
+          19
         ],
         Error: new Error()
       };
 }
 
 function add(x, data, tree) {
-  if (!tree) {
+  if (/* tag */typeof tree === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -161,18 +163,18 @@ var m = List.fold_left((function (acc, param) {
 function find(px, _x) {
   while(true) {
     var x = _x;
-    if (x) {
-      var c = Caml.int_compare(px, x._1);
-      if (c === 0) {
-        return x._2;
-      }
-      _x = c < 0 ? x._0 : x._3;
-      continue ;
+    if (/* tag */typeof x === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(px, x._1);
+    if (c === 0) {
+      return x._2;
+    }
+    _x = c < 0 ? x._0 : x._3;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/inline_map_test.js b/jscomp/test/inline_map_test.js
index 4c4186d72f..538a70d250 100644
--- a/jscomp/test/inline_map_test.js
+++ b/jscomp/test/inline_map_test.js
@@ -5,10 +5,10 @@ var Caml = require("../../lib/js/caml.js");
 var List = require("../../lib/js/list.js");
 
 function height(param) {
-  if (param) {
-    return param._4;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._4;
   }
 }
 
@@ -25,26 +25,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l._4 : 0;
-  var hr = r ? r._4 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._4;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._4;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._3;
-      var ld = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l._3;
+    var ld = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr._0), lr._1, lr._2, create(lr._3, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -60,23 +62,23 @@ function bal(l, x, d, r) {
             _4: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._3;
-    var rd = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r._3;
+  var rd = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl._0), rl._1, rl._2, create(rl._3, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -85,7 +87,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -117,18 +119,18 @@ function add(x, data, param) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.int_compare(x, param._1);
-      if (c === 0) {
-        return param._2;
-      }
-      _param = c < 0 ? param._0 : param._3;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(x, param._1);
+    if (c === 0) {
+      return param._2;
+    }
+    _param = c < 0 ? param._0 : param._3;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/inline_record_test.js b/jscomp/test/inline_record_test.js
index 43cb890ec9..6b0674f355 100644
--- a/jscomp/test/inline_record_test.js
+++ b/jscomp/test/inline_record_test.js
@@ -181,13 +181,13 @@ if (v6.RE_EXN_ID === A4) {
 eq("File \"inline_record_test.ml\", line 87, characters 6-13", tmp$3, 11);
 
 function ff1(x) {
-  if (x) {
+  if (/* tag */typeof x === "number") {
+    return /* A1 */0;
+  } else {
     return /* A0 */{
             lbl: x.lbl + 1 | 0,
             more: x.more
           };
-  } else {
-    return /* A1 */0;
   }
 }
 
diff --git a/jscomp/test/int64_test.js b/jscomp/test/int64_test.js
index 989c15230c..59f6d3a7ef 100644
--- a/jscomp/test/int64_test.js
+++ b/jscomp/test/int64_test.js
@@ -2147,7 +2147,7 @@ function eq(loc, x, y) {
 function id(loc, x) {
   var float_value = Caml_int64.float_of_bits(x);
   var match = Pervasives.classify_float(float_value);
-  if (match >= 4) {
+  if (match === /* FP_nan */4) {
     return ;
   } else {
     return eq(loc, Caml_int64.bits_of_float(float_value), x);
diff --git a/jscomp/test/int_map.js b/jscomp/test/int_map.js
index 623f9c2d63..fe3b276233 100644
--- a/jscomp/test/int_map.js
+++ b/jscomp/test/int_map.js
@@ -5,10 +5,10 @@ var Curry = require("../../lib/js/curry.js");
 var Caml_option = require("../../lib/js/caml_option.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -35,26 +35,28 @@ function singleton(x, d) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -70,23 +72,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -95,15 +97,15 @@ function bal(l, x, d, r) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -149,65 +151,65 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.int_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -219,7 +221,7 @@ function find_first_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -244,47 +246,47 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -296,7 +298,7 @@ function find_last_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -321,7 +323,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var c = Caml.int_compare(x, param.v);
@@ -336,7 +338,7 @@ function find_opt(x, _param) {
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.int_compare(x, param.v);
@@ -351,32 +353,32 @@ function mem(x, _param) {
 function min_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return [
               param.v,
               param.d
@@ -390,32 +392,32 @@ function min_binding_opt(_param) {
 function max_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return [
               param.v,
               param.d
@@ -427,26 +429,26 @@ function max_binding_opt(_param) {
 }
 
 function remove_min_binding(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_binding(l), param.v, param.d, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Map.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_binding(l), param.v, param.d, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function merge(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -454,7 +456,7 @@ function merge(t1, t2) {
 }
 
 function remove(x, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -482,63 +484,63 @@ function remove(x, m) {
 }
 
 function update(x, f, m) {
-  if (m) {
-    var r = m.r;
-    var d = m.d;
-    var v = m.v;
-    var l = m.l;
-    var c = Caml.int_compare(x, v);
-    if (c === 0) {
-      var data = Curry._1(f, Caml_option.some(d));
-      if (data === undefined) {
-        return merge(l, r);
-      }
-      var data$1 = Caml_option.valFromOption(data);
-      if (d === data$1) {
-        return m;
-      } else {
-        return /* Node */{
-                l: l,
-                v: x,
-                d: data$1,
-                r: r,
-                h: m.h
-              };
-      }
+  if (/* tag */typeof m === "number") {
+    var data = Curry._1(f, undefined);
+    if (data !== undefined) {
+      return /* Node */{
+              l: /* Empty */0,
+              v: x,
+              d: Caml_option.valFromOption(data),
+              r: /* Empty */0,
+              h: 1
+            };
+    } else {
+      return /* Empty */0;
     }
-    if (c < 0) {
-      var ll = update(x, f, l);
-      if (l === ll) {
-        return m;
-      } else {
-        return bal(ll, v, d, r);
-      }
+  }
+  var r = m.r;
+  var d = m.d;
+  var v = m.v;
+  var l = m.l;
+  var c = Caml.int_compare(x, v);
+  if (c === 0) {
+    var data$1 = Curry._1(f, Caml_option.some(d));
+    if (data$1 === undefined) {
+      return merge(l, r);
+    }
+    var data$2 = Caml_option.valFromOption(data$1);
+    if (d === data$2) {
+      return m;
+    } else {
+      return /* Node */{
+              l: l,
+              v: x,
+              d: data$2,
+              r: r,
+              h: m.h
+            };
     }
-    var rr = update(x, f, r);
-    if (r === rr) {
+  }
+  if (c < 0) {
+    var ll = update(x, f, l);
+    if (l === ll) {
       return m;
     } else {
-      return bal(l, v, d, rr);
+      return bal(ll, v, d, r);
     }
   }
-  var data$2 = Curry._1(f, undefined);
-  if (data$2 !== undefined) {
-    return /* Node */{
-            l: /* Empty */0,
-            v: x,
-            d: Caml_option.valFromOption(data$2),
-            r: /* Empty */0,
-            h: 1
-          };
+  var rr = update(x, f, r);
+  if (r === rr) {
+    return m;
   } else {
-    return /* Empty */0;
+    return bal(l, v, d, rr);
   }
 }
 
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -549,7 +551,7 @@ function iter(f, _param) {
 }
 
 function map(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var l$p = map(f, param.l);
@@ -565,7 +567,7 @@ function map(f, param) {
 }
 
 function mapi(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param.v;
@@ -585,7 +587,7 @@ function fold(f, _m, _accu) {
   while(true) {
     var accu = _accu;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return accu;
     }
     _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -597,7 +599,7 @@ function fold(f, _m, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._2(p, param.v, param.d)) {
@@ -614,7 +616,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._2(p, param.v, param.d)) {
@@ -629,30 +631,30 @@ function exists(p, _param) {
 }
 
 function add_min_binding(k, x, param) {
-  if (param) {
-    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
   }
 }
 
 function add_max_binding(k, x, param) {
-  if (param) {
-    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
   }
 }
 
 function join(l, v, d, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_binding(v, d, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_binding(v, d, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, l.d, join(l.r, v, d, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -663,10 +665,10 @@ function join(l, v, d, r) {
 }
 
 function concat(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -682,7 +684,7 @@ function concat_or_join(t1, v, d, t2) {
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             undefined,
@@ -718,43 +720,46 @@ function split(x, param) {
 }
 
 function merge$1(f, s1, s2) {
-  if (s1) {
+  if (/* tag */typeof s1 === "number") {
+    if (/* tag */typeof s2 === "number") {
+      return /* Empty */0;
+    }
+    
+  } else {
     var v1 = s1.v;
     if (s1.h >= height(s2)) {
       var match = split(v1, s2);
       return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
     }
     
-  } else if (!s2) {
-    return /* Empty */0;
   }
-  if (s2) {
-    var v2 = s2.v;
-    var match$1 = split(v2, s1);
-    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+  if (/* tag */typeof s2 === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "map.ml",
+            393,
+            10
+          ],
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "map.ml",
-          393,
-          10
-        ],
-        Error: new Error()
-      };
+  var v2 = s2.v;
+  var match$1 = split(v2, s1);
+  return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
 }
 
 function union(f, s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var d1 = s1.d;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var d2 = s2.d;
   var v2 = s2.v;
-  var d1 = s1.d;
-  var v1 = s1.v;
   if (s1.h >= s2.h) {
     var match = split(v1, s2);
     var d2$1 = match[1];
@@ -778,7 +783,7 @@ function union(f, s1, s2) {
 }
 
 function filter(p, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -800,7 +805,7 @@ function filter(p, m) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -832,7 +837,7 @@ function cons_enum(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -852,14 +857,14 @@ function compare(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.int_compare(e1._0, e2._0);
@@ -882,14 +887,14 @@ function equal(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (e1._0 !== e2._0) {
@@ -905,10 +910,10 @@ function equal(cmp, m1, m2) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -916,7 +921,7 @@ function bindings_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
diff --git a/jscomp/test/js_json_test.js b/jscomp/test/js_json_test.js
index e9722028f1..64359ede10 100644
--- a/jscomp/test/js_json_test.js
+++ b/jscomp/test/js_json_test.js
@@ -61,7 +61,7 @@ var v = JSON.parse(" { \"x\" : [1, 2, 3 ] } ");
 
 add_test("File \"js_json_test.ml\", line 24, characters 11-18", (function (param) {
         var ty = Js_json.classify(v);
-        if (typeof ty === "number") {
+        if (/* tag */typeof ty === "number") {
           return {
                   TAG: /* Ok */4,
                   _0: false
@@ -81,7 +81,7 @@ add_test("File \"js_json_test.ml\", line 24, characters 11-18", (function (param
                 };
         }
         var ty2 = Js_json.classify(Caml_option.valFromOption(v$1));
-        if (typeof ty2 === "number") {
+        if (/* tag */typeof ty2 === "number") {
           return {
                   TAG: /* Ok */4,
                   _0: false
@@ -95,7 +95,7 @@ add_test("File \"js_json_test.ml\", line 24, characters 11-18", (function (param
         }
         ty2._0.forEach(function (x) {
               var ty3 = Js_json.classify(x);
-              if (typeof ty3 === "number") {
+              if (/* tag */typeof ty3 === "number") {
                 throw {
                       RE_EXN_ID: "Assert_failure",
                       _1: [
@@ -131,8 +131,8 @@ var json = JSON.parse(JSON.stringify(null));
 
 var ty = Js_json.classify(json);
 
-if (typeof ty === "number") {
-  if (ty >= 2) {
+if (/* tag */typeof ty === "number") {
+  if (ty === /* JSONNull */2) {
     add_test("File \"js_json_test.ml\", line 55, characters 24-31", (function (param) {
             return {
                     TAG: /* Ok */4,
@@ -162,7 +162,7 @@ var json$1 = JSON.parse(JSON.stringify("test string"));
 
 var ty$1 = Js_json.classify(json$1);
 
-if (typeof ty$1 === "number") {
+if (/* tag */typeof ty$1 === "number") {
   add_test("File \"js_json_test.ml\", line 66, characters 16-23", (function (param) {
           return {
                   TAG: /* Ok */4,
@@ -186,7 +186,7 @@ var ty$2 = Js_json.classify(json$2);
 
 var exit = 0;
 
-if (typeof ty$2 === "number" || ty$2.TAG !== /* JSONNumber */1) {
+if (/* tag */typeof ty$2 === "number" || ty$2.TAG !== /* JSONNumber */1) {
   exit = 1;
 } else {
   eq("File \"js_json_test.ml\", line 75, characters 25-32", ty$2._0, 1.23456789);
@@ -207,7 +207,7 @@ var ty$3 = Js_json.classify(json$3);
 
 var exit$1 = 0;
 
-if (typeof ty$3 === "number" || ty$3.TAG !== /* JSONNumber */1) {
+if (/* tag */typeof ty$3 === "number" || ty$3.TAG !== /* JSONNumber */1) {
   exit$1 = 1;
 } else {
   eq("File \"js_json_test.ml\", line 85, characters 25-32", ty$3._0 | 0, -1347440721);
@@ -225,7 +225,7 @@ if (exit$1 === 1) {
 function test(v) {
   var json = JSON.parse(JSON.stringify(v));
   var ty = Js_json.classify(json);
-  if (typeof ty !== "number") {
+  if (/* tag */typeof ty !== "number") {
     return add_test("File \"js_json_test.ml\", line 97, characters 18-25", (function (param) {
                   return {
                           TAG: /* Ok */4,
@@ -238,14 +238,13 @@ function test(v) {
         return eq("File \"js_json_test.ml\", line 96, characters 25-32", false, v);
     case /* JSONTrue */1 :
         return eq("File \"js_json_test.ml\", line 95, characters 24-31", true, v);
-    case /* JSONNull */2 :
-        return add_test("File \"js_json_test.ml\", line 97, characters 18-25", (function (param) {
-                      return {
-                              TAG: /* Ok */4,
-                              _0: false
-                            };
-                    }));
-    
+    default:
+      return add_test("File \"js_json_test.ml\", line 97, characters 18-25", (function (param) {
+                    return {
+                            TAG: /* Ok */4,
+                            _0: false
+                          };
+                  }));
   }
 }
 
@@ -278,7 +277,7 @@ var json$4 = JSON.parse(JSON.stringify(dict));
 
 var ty$4 = Js_json.classify(json$4);
 
-if (typeof ty$4 === "number") {
+if (/* tag */typeof ty$4 === "number") {
   add_test("File \"js_json_test.ml\", line 135, characters 16-23", (function (param) {
           return {
                   TAG: /* Ok */4,
@@ -288,7 +287,7 @@ if (typeof ty$4 === "number") {
 } else if (ty$4.TAG === /* JSONObject */2) {
   var x = ty$4._0;
   var ta = Js_json.classify(option_get(Js_dict.get(x, "a")));
-  if (typeof ta === "number") {
+  if (/* tag */typeof ta === "number") {
     add_test("File \"js_json_test.ml\", line 133, characters 18-25", (function (param) {
             return {
                     TAG: /* Ok */4,
@@ -305,7 +304,7 @@ if (typeof ty$4 === "number") {
             }));
     } else {
       var ty$5 = Js_json.classify(option_get(Js_dict.get(x, "b")));
-      if (typeof ty$5 === "number") {
+      if (/* tag */typeof ty$5 === "number") {
         add_test("File \"js_json_test.ml\", line 131, characters 22-29", (function (param) {
                 return {
                         TAG: /* Ok */4,
@@ -349,7 +348,7 @@ if (typeof ty$4 === "number") {
 
 function eq_at_i(loc, json, i, kind, expected) {
   var ty = Js_json.classify(json);
-  if (typeof ty === "number") {
+  if (/* tag */typeof ty === "number") {
     return add_test(loc, (function (param) {
                   return {
                           TAG: /* Ok */4,
@@ -368,7 +367,7 @@ function eq_at_i(loc, json, i, kind, expected) {
   var ty$1 = Js_json.classify(Caml_array.get(ty._0, i));
   switch (kind) {
     case /* String */0 :
-        if (typeof ty$1 === "number") {
+        if (/* tag */typeof ty$1 === "number") {
           return add_test(loc, (function (param) {
                         return {
                                 TAG: /* Ok */4,
@@ -386,7 +385,7 @@ function eq_at_i(loc, json, i, kind, expected) {
                       }));
         }
     case /* Number */1 :
-        if (typeof ty$1 === "number") {
+        if (/* tag */typeof ty$1 === "number") {
           return add_test(loc, (function (param) {
                         return {
                                 TAG: /* Ok */4,
@@ -404,7 +403,7 @@ function eq_at_i(loc, json, i, kind, expected) {
                       }));
         }
     case /* Object */2 :
-        if (typeof ty$1 === "number") {
+        if (/* tag */typeof ty$1 === "number") {
           return add_test(loc, (function (param) {
                         return {
                                 TAG: /* Ok */4,
@@ -422,7 +421,7 @@ function eq_at_i(loc, json, i, kind, expected) {
                       }));
         }
     case /* Array */3 :
-        if (typeof ty$1 === "number") {
+        if (/* tag */typeof ty$1 === "number") {
           return add_test(loc, (function (param) {
                         return {
                                 TAG: /* Ok */4,
@@ -440,7 +439,7 @@ function eq_at_i(loc, json, i, kind, expected) {
                       }));
         }
     case /* Boolean */4 :
-        if (typeof ty$1 !== "number") {
+        if (/* tag */typeof ty$1 !== "number") {
           return add_test(loc, (function (param) {
                         return {
                                 TAG: /* Ok */4,
@@ -453,18 +452,17 @@ function eq_at_i(loc, json, i, kind, expected) {
               return eq(loc, false, expected);
           case /* JSONTrue */1 :
               return eq(loc, true, expected);
-          case /* JSONNull */2 :
-              return add_test(loc, (function (param) {
-                            return {
-                                    TAG: /* Ok */4,
-                                    _0: false
-                                  };
-                          }));
-          
+          default:
+            return add_test(loc, (function (param) {
+                          return {
+                                  TAG: /* Ok */4,
+                                  _0: false
+                                };
+                        }));
         }
     case /* Null */5 :
-        if (typeof ty$1 === "number") {
-          if (ty$1 >= 2) {
+        if (/* tag */typeof ty$1 === "number") {
+          if (ty$1 === /* JSONNull */2) {
             return add_test(loc, (function (param) {
                           return {
                                   TAG: /* Ok */4,
@@ -577,7 +575,7 @@ var json$10 = JSON.parse(JSON.stringify(a$3));
 
 var ty$6 = Js_json.classify(json$10);
 
-if (typeof ty$6 === "number") {
+if (/* tag */typeof ty$6 === "number") {
   add_test("File \"js_json_test.ml\", line 283, characters 16-23", (function (param) {
           return {
                   TAG: /* Ok */4,
@@ -586,7 +584,7 @@ if (typeof ty$6 === "number") {
         }));
 } else if (ty$6.TAG === /* JSONArray */3) {
   var ty$7 = Js_json.classify(Caml_array.get(ty$6._0, 1));
-  if (typeof ty$7 === "number") {
+  if (/* tag */typeof ty$7 === "number") {
     add_test("File \"js_json_test.ml\", line 281, characters 18-25", (function (param) {
             return {
                     TAG: /* Ok */4,
@@ -595,7 +593,7 @@ if (typeof ty$6 === "number") {
           }));
   } else if (ty$7.TAG === /* JSONObject */2) {
     var ty$8 = Js_json.classify(option_get(Js_dict.get(ty$7._0, "a")));
-    if (typeof ty$8 === "number") {
+    if (/* tag */typeof ty$8 === "number") {
       add_test("File \"js_json_test.ml\", line 279, characters 20-27", (function (param) {
               return {
                       TAG: /* Ok */4,
diff --git a/jscomp/test/large_record_duplication_test.js b/jscomp/test/large_record_duplication_test.js
index 71f8aceb68..b29c79ec92 100644
--- a/jscomp/test/large_record_duplication_test.js
+++ b/jscomp/test/large_record_duplication_test.js
@@ -83,14 +83,15 @@ var v1 = /* A0 */{
 };
 
 function get_x0(x) {
-  if (x) {
+  if (/* tag */typeof x === "number") {
+    return ;
+  } else {
     return x.x0;
   }
-  
 }
 
 function f1(x) {
-  if (!x) {
+  if (/* tag */typeof x === "number") {
     return /* A1 */0;
   }
   var newrecord = Caml_obj.obj_dup(x);
diff --git a/jscomp/test/map_find_test.js b/jscomp/test/map_find_test.js
index 63c2e566d3..0eb6f50d36 100644
--- a/jscomp/test/map_find_test.js
+++ b/jscomp/test/map_find_test.js
@@ -5,10 +5,10 @@ var Caml = require("../../lib/js/caml.js");
 var List = require("../../lib/js/list.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -25,26 +25,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -60,23 +62,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -85,7 +87,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -131,18 +133,18 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.int_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
@@ -175,10 +177,10 @@ var m = List.fold_left((function (acc, param) {
     });
 
 function height$1(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -195,26 +197,28 @@ function create$1(l, x, d, r) {
 }
 
 function bal$1(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$1(ll) >= height$1(lr)) {
-        return create$1(ll, lv, ld, create$1(lr, x, d, r));
-      }
-      if (lr) {
-        return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$1(ll) >= height$1(lr)) {
+      return create$1(ll, lv, ld, create$1(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -230,23 +234,23 @@ function bal$1(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$1(rr) >= height$1(rl)) {
-      return create$1(create$1(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$1(rr) >= height$1(rl)) {
+    return create$1(create$1(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -255,7 +259,7 @@ function bal$1(l, x, d, r) {
 }
 
 function add$1(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -301,18 +305,18 @@ function add$1(x, data, m) {
 function find$1(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.string_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.string_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/map_test.js b/jscomp/test/map_test.js
index 2e76cb009b..34d7017603 100644
--- a/jscomp/test/map_test.js
+++ b/jscomp/test/map_test.js
@@ -6,10 +6,10 @@ var List = require("../../lib/js/list.js");
 var Curry = require("../../lib/js/curry.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -26,26 +26,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -61,23 +63,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -86,7 +88,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -133,7 +135,7 @@ function cons_enum(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -153,14 +155,14 @@ function compare(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.int_compare(e1._0, e2._0);
@@ -183,14 +185,14 @@ function equal(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (e1._0 !== e2._0) {
@@ -206,18 +208,18 @@ function equal(cmp, m1, m2) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
 function height$1(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -234,26 +236,28 @@ function create$1(l, x, d, r) {
 }
 
 function bal$1(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$1(ll) >= height$1(lr)) {
-        return create$1(ll, lv, ld, create$1(lr, x, d, r));
-      }
-      if (lr) {
-        return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$1(ll) >= height$1(lr)) {
+      return create$1(ll, lv, ld, create$1(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$1(create$1(ll, lv, ld, lr.l), lr.v, lr.d, create$1(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -269,23 +273,23 @@ function bal$1(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$1(rr) >= height$1(rl)) {
-      return create$1(create$1(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$1(rr) >= height$1(rl)) {
+    return create$1(create$1(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$1(create$1(l, x, d, rl.l), rl.v, rl.d, create$1(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -294,7 +298,7 @@ function bal$1(l, x, d, r) {
 }
 
 function add$1(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -340,18 +344,18 @@ function add$1(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.string_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.string_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/mario_game.js b/jscomp/test/mario_game.js
index d9c6052b01..4b2195e92c 100644
--- a/jscomp/test/mario_game.js
+++ b/jscomp/test/mario_game.js
@@ -554,7 +554,7 @@ function make_type(typ, dir) {
         }
     case /* SBlock */3 :
         var x$1 = typ._0;
-        if (typeof x$1 !== "number") {
+        if (/* tag */typeof x$1 !== "number") {
           return setup_sprite(undefined, undefined, undefined, "blocks.png", 4, 15, [
                       16,
                       16
@@ -699,18 +699,20 @@ function pair_to_xy(pair) {
 }
 
 function make_type$1(typ, ctx) {
-  if (typ === 2 || typ === 1) {
-    return {
-            sprite: make_particle$1(typ, ctx),
-            rot: 0,
-            lifetime: 300
-          };
-  } else {
-    return {
-            sprite: make_particle$1(typ, ctx),
-            rot: 0,
-            lifetime: 30
-          };
+  switch (typ) {
+    case /* BrickChunkL */1 :
+    case /* BrickChunkR */2 :
+        return {
+                sprite: make_particle$1(typ, ctx),
+                rot: 0,
+                lifetime: 300
+              };
+    default:
+      return {
+              sprite: make_particle$1(typ, ctx),
+              rot: 0,
+              lifetime: 30
+            };
   }
 }
 
@@ -814,14 +816,16 @@ function make_type$2(x) {
         return setup_obj(undefined, 2.8, undefined);
     case /* SEnemy */1 :
         var x$1 = x._0;
-        if (x$1 >= 3) {
-          return setup_obj(undefined, 3, undefined);
-        } else {
-          return setup_obj(undefined, undefined, undefined);
+        switch (x$1) {
+          case /* GKoopaShell */3 :
+          case /* RKoopaShell */4 :
+              return setup_obj(undefined, 3, undefined);
+          default:
+            return setup_obj(undefined, undefined, undefined);
         }
     case /* SItem */2 :
         var x$2 = x._0;
-        if (x$2 >= 3) {
+        if (x$2 === /* Coin */3) {
           return setup_obj(false, undefined, undefined);
         } else {
           return setup_obj(undefined, undefined, undefined);
@@ -1088,29 +1092,38 @@ function normalize_origin(pos, spr) {
 
 function collide_block(check_xOpt, dir, obj) {
   var check_x = check_xOpt !== undefined ? check_xOpt : true;
-  if (dir !== 1) {
-    if (dir !== 0) {
-      if (check_x) {
-        obj.vel.x = 0;
+  switch (dir) {
+    case /* North */0 :
+        obj.vel.y = -0.001;
         return ;
-      } else {
+    case /* South */1 :
+        obj.vel.y = 0;
+        obj.grounded = true;
+        obj.jumping = false;
         return ;
-      }
-    } else {
-      obj.vel.y = -0.001;
-      return ;
-    }
-  } else {
-    obj.vel.y = 0;
-    obj.grounded = true;
-    obj.jumping = false;
+    case /* East */2 :
+    case /* West */3 :
+        break;
+    
+  }
+  if (check_x) {
+    obj.vel.x = 0;
     return ;
   }
+  
+}
+
+function opposite_dir(dir) {
+  if (dir === /* Left */0) {
+    return /* Right */1;
+  } else {
+    return /* Left */0;
+  }
 }
 
 function reverse_left_right(obj) {
   obj.vel.x = - obj.vel.x;
-  obj.dir = obj.dir ? /* Left */0 : /* Right */1;
+  obj.dir = opposite_dir(obj.dir);
 }
 
 function evolve_enemy(player_dir, typ, spr, obj, context) {
@@ -1212,7 +1225,7 @@ function spawn_above(player_dir, obj, typ, context) {
       ]);
   var item_obj = item._2;
   item_obj.pos.y = item_obj.pos.y - item._1.params.frame_size[1];
-  item_obj.dir = player_dir ? /* Left */0 : /* Right */1;
+  item_obj.dir = opposite_dir(player_dir);
   set_vel_to_speed(item_obj);
   return item;
 }
@@ -1323,16 +1336,15 @@ function kill(collid, ctx) {
               hd: make_score(o.score, pos, ctx),
               tl: /* [] */0
             }) : /* [] */0;
-        var remains = collid._0 !== 0 ? /* [] */0 : ({
+        var remains;
+        remains = collid._0 === /* Goomba */0 ? ({
               hd: make$1(undefined, undefined, /* GoombaSquish */0, pos, ctx),
               tl: /* [] */0
-            });
+            }) : /* [] */0;
         return Pervasives.$at(score, remains);
     case /* Item */2 :
         var o$1 = collid._2;
-        if (collid._0 !== 0) {
-          return /* [] */0;
-        } else {
+        if (collid._0 === /* Mushroom */0) {
           return {
                   hd: make_score(o$1.score, [
                         o$1.pos.x,
@@ -1340,10 +1352,16 @@ function kill(collid, ctx) {
                       ], ctx),
                   tl: /* [] */0
                 };
+        } else {
+          return /* [] */0;
         }
     case /* Block */3 :
         var o$2 = collid._2;
-        if (collid._0 !== 1) {
+        var tmp = collid._0;
+        if (/* tag */typeof tmp !== "number") {
+          return /* [] */0;
+        }
+        if (tmp !== /* Brick */1) {
           return /* [] */0;
         }
         var pos_0$1 = o$2.pos.x;
@@ -1651,20 +1669,20 @@ function process_collision(dir, c1, c2, state) {
               var o2$3 = c2._2;
               var s2$2 = c2._1;
               var typ$1 = c2._0;
-              if (dir !== 1) {
-                s1$1 = s1$2;
-                o1$1 = o1$3;
-                t2 = typ$1;
-                s2$1 = s2$2;
-                o2$1 = o2$3;
-                exit = 2;
-              } else {
+              if (dir === /* South */1) {
                 s1 = s1$2;
                 o1 = o1$3;
                 typ = typ$1;
                 s2 = s2$2;
                 o2 = o2$3;
                 exit = 1;
+              } else {
+                s1$1 = s1$2;
+                o1$1 = o1$3;
+                t2 = typ$1;
+                s2$1 = s2$2;
+                o2$1 = o2$3;
+                exit = 2;
               }
               break;
           case /* Item */2 :
@@ -1676,65 +1694,78 @@ function process_collision(dir, c1, c2, state) {
           case /* Block */3 :
               var o2$4 = c2._2;
               var t = c2._0;
-              if (dir !== 0) {
-                if (t === 4) {
-                  game_win(state.ctx);
-                  return [
-                          undefined,
-                          undefined
-                        ];
-                } else if (dir !== 1) {
-                  collide_block(undefined, dir, o1$3);
-                  return [
-                          undefined,
-                          undefined
-                        ];
+              if (dir === /* North */0) {
+                if (/* tag */typeof t === "number") {
+                  switch (t) {
+                    case /* Brick */1 :
+                        if (c1._0 === /* BigM */0) {
+                          collide_block(undefined, dir, o1$3);
+                          dec_health(o2$4);
+                          return [
+                                  undefined,
+                                  undefined
+                                ];
+                        } else {
+                          collide_block(undefined, dir, o1$3);
+                          return [
+                                  undefined,
+                                  undefined
+                                ];
+                        }
+                    case /* Panel */4 :
+                        game_win(state.ctx);
+                        return [
+                                undefined,
+                                undefined
+                              ];
+                    default:
+                      collide_block(undefined, dir, o1$3);
+                      return [
+                              undefined,
+                              undefined
+                            ];
+                  }
                 } else {
-                  state.multiplier = 1;
+                  var updated_block = evolve_block(o2$4, context);
+                  var spawned_item = spawn_above(o1$3.dir, o2$4, t._0, context);
                   collide_block(undefined, dir, o1$3);
                   return [
-                          undefined,
-                          undefined
+                          spawned_item,
+                          updated_block
                         ];
                 }
-              }
-              if (typeof t === "number") {
-                if (t !== 1) {
-                  if (t !== 4) {
-                    collide_block(undefined, dir, o1$3);
+              } else {
+                var exit$1 = 0;
+                if (/* tag */typeof t === "number") {
+                  if (t === /* Panel */4) {
+                    game_win(state.ctx);
                     return [
                             undefined,
                             undefined
                           ];
-                  } else {
-                    game_win(state.ctx);
+                  }
+                  exit$1 = 4;
+                } else {
+                  exit$1 = 4;
+                }
+                if (exit$1 === 4) {
+                  if (dir === /* South */1) {
+                    state.multiplier = 1;
+                    collide_block(undefined, dir, o1$3);
                     return [
                             undefined,
                             undefined
                           ];
                   }
-                } else if (c1._0 === /* BigM */0) {
-                  collide_block(undefined, dir, o1$3);
-                  dec_health(o2$4);
-                  return [
-                          undefined,
-                          undefined
-                        ];
-                } else {
                   collide_block(undefined, dir, o1$3);
                   return [
                           undefined,
                           undefined
                         ];
                 }
+                
               }
-              var updated_block = evolve_block(o2$4, context);
-              var spawned_item = spawn_above(o1$3.dir, o2$4, t._0, context);
-              collide_block(undefined, dir, o1$3);
-              return [
-                      spawned_item,
-                      updated_block
-                    ];
+              break;
           
         }
         break;
@@ -1746,29 +1777,103 @@ function process_collision(dir, c1, c2, state) {
           case /* Player */0 :
               var o1$5 = c2._2;
               var s1$4 = c2._1;
-              if (dir !== 0) {
-                s1$1 = s1$4;
-                o1$1 = o1$5;
-                t2 = t1;
-                s2$1 = s1$3;
-                o2$1 = o1$4;
-                exit = 2;
-              } else {
+              if (dir === /* North */0) {
                 s1 = s1$4;
                 o1 = o1$5;
                 typ = t1;
                 s2 = s1$3;
                 o2 = o1$4;
                 exit = 1;
+              } else {
+                s1$1 = s1$4;
+                o1$1 = o1$5;
+                t2 = t1;
+                s2$1 = s1$3;
+                o2$1 = o1$4;
+                exit = 2;
               }
               break;
           case /* Enemy */1 :
               var t2$2 = c2._0;
               var s2$3 = c2._1;
               var o2$5 = c2._2;
-              if (t1 !== 3) {
-                if (t1 < 4) {
-                  if (t2$2 >= 3) {
+              var exit$2 = 0;
+              switch (t1) {
+                case /* GKoopaShell */3 :
+                    switch (t2$2) {
+                      case /* GKoopaShell */3 :
+                      case /* RKoopaShell */4 :
+                          exit$2 = 1;
+                          break;
+                      default:
+                        exit$2 = 2;
+                    }
+                    break;
+                case /* RKoopaShell */4 :
+                    switch (t2$2) {
+                      case /* GKoopaShell */3 :
+                      case /* RKoopaShell */4 :
+                          exit$2 = 1;
+                          break;
+                      default:
+                        exit$2 = 2;
+                    }
+                    break;
+                default:
+                  switch (t2$2) {
+                    case /* GKoopaShell */3 :
+                    case /* RKoopaShell */4 :
+                        exit$2 = 3;
+                        break;
+                    default:
+                      var exit$3 = 0;
+                      switch (dir) {
+                        case /* North */0 :
+                        case /* South */1 :
+                            return [
+                                    undefined,
+                                    undefined
+                                  ];
+                        case /* East */2 :
+                        case /* West */3 :
+                            exit$3 = 4;
+                            break;
+                        
+                      }
+                      if (exit$3 === 4) {
+                        rev_dir(o1$4, t1, s1$3);
+                        rev_dir(o2$5, t2$2, s2$3);
+                        return [
+                                undefined,
+                                undefined
+                              ];
+                      }
+                      
+                  }
+              }
+              switch (exit$2) {
+                case 1 :
+                    dec_health(o1$4);
+                    dec_health(o2$5);
+                    return [
+                            undefined,
+                            undefined
+                          ];
+                case 2 :
+                    if (o1$4.vel.x === 0) {
+                      rev_dir(o2$5, t2$2, s2$3);
+                      return [
+                              undefined,
+                              undefined
+                            ];
+                    } else {
+                      dec_health(o2$5);
+                      return [
+                              undefined,
+                              undefined
+                            ];
+                    }
+                case 3 :
                     if (o2$5.vel.x === 0) {
                       rev_dir(o1$4, t1, s1$3);
                       return [
@@ -1782,49 +1887,7 @@ function process_collision(dir, c1, c2, state) {
                               undefined
                             ];
                     }
-                  } else if (dir >= 2) {
-                    rev_dir(o1$4, t1, s1$3);
-                    rev_dir(o2$5, t2$2, s2$3);
-                    return [
-                            undefined,
-                            undefined
-                          ];
-                  } else {
-                    return [
-                            undefined,
-                            undefined
-                          ];
-                  }
-                }
-                if (t2$2 >= 3) {
-                  dec_health(o1$4);
-                  dec_health(o2$5);
-                  return [
-                          undefined,
-                          undefined
-                        ];
-                }
                 
-              } else if (t2$2 >= 3) {
-                dec_health(o1$4);
-                dec_health(o2$5);
-                return [
-                        undefined,
-                        undefined
-                      ];
-              }
-              if (o1$4.vel.x === 0) {
-                rev_dir(o2$5, t2$2, s2$3);
-                return [
-                        undefined,
-                        undefined
-                      ];
-              } else {
-                dec_health(o2$5);
-                return [
-                        undefined,
-                        undefined
-                      ];
               }
           case /* Item */2 :
               return [
@@ -1834,43 +1897,79 @@ function process_collision(dir, c1, c2, state) {
           case /* Block */3 :
               var o2$6 = c2._2;
               var t2$3 = c2._0;
-              if (dir >= 2) {
-                if (t1 >= 3) {
-                  if (typeof t2$3 === "number") {
-                    if (t2$3 !== 1) {
+              var exit$4 = 0;
+              switch (dir) {
+                case /* North */0 :
+                case /* South */1 :
+                    collide_block(undefined, dir, o1$4);
+                    return [
+                            undefined,
+                            undefined
+                          ];
+                case /* East */2 :
+                case /* West */3 :
+                    exit$4 = 4;
+                    break;
+                
+              }
+              if (exit$4 === 4) {
+                var exit$5 = 0;
+                var typ$2;
+                switch (t1) {
+                  case /* GKoopaShell */3 :
+                      if (/* tag */typeof t2$3 === "number") {
+                        if (t2$3 === /* Brick */1) {
+                          dec_health(o2$6);
+                          reverse_left_right(o1$4);
+                          return [
+                                  undefined,
+                                  undefined
+                                ];
+                        }
+                        exit$5 = 5;
+                      } else {
+                        typ$2 = t2$3._0;
+                        exit$5 = 6;
+                      }
+                      break;
+                  case /* RKoopaShell */4 :
+                      if (/* tag */typeof t2$3 === "number") {
+                        if (t2$3 === /* Brick */1) {
+                          dec_health(o2$6);
+                          reverse_left_right(o1$4);
+                          return [
+                                  undefined,
+                                  undefined
+                                ];
+                        }
+                        exit$5 = 5;
+                      } else {
+                        typ$2 = t2$3._0;
+                        exit$5 = 6;
+                      }
+                      break;
+                  default:
+                    exit$5 = 5;
+                }
+                switch (exit$5) {
+                  case 5 :
                       rev_dir(o1$4, t1, s1$3);
                       return [
                               undefined,
                               undefined
                             ];
-                    } else {
-                      dec_health(o2$6);
-                      reverse_left_right(o1$4);
+                  case 6 :
+                      var updated_block$1 = evolve_block(o2$6, context);
+                      var spawned_item$1 = spawn_above(o1$4.dir, o2$6, typ$2, context);
+                      rev_dir(o1$4, t1, s1$3);
                       return [
-                              undefined,
-                              undefined
+                              updated_block$1,
+                              spawned_item$1
                             ];
-                    }
-                  }
-                  var updated_block$1 = evolve_block(o2$6, context);
-                  var spawned_item$1 = spawn_above(o1$4.dir, o2$6, t2$3._0, context);
-                  rev_dir(o1$4, t1, s1$3);
-                  return [
-                          updated_block$1,
-                          spawned_item$1
-                        ];
+                  
                 }
-                rev_dir(o1$4, t1, s1$3);
-                return [
-                        undefined,
-                        undefined
-                      ];
               }
-              collide_block(undefined, dir, o1$4);
-              return [
-                      undefined,
-                      undefined
-                    ];
+              break;
           
         }
         break;
@@ -1890,18 +1989,22 @@ function process_collision(dir, c1, c2, state) {
                       undefined
                     ];
           case /* Block */3 :
-              if (dir >= 2) {
-                reverse_left_right(o2$7);
-                return [
-                        undefined,
-                        undefined
-                      ];
-              } else {
-                collide_block(undefined, dir, o2$7);
-                return [
-                        undefined,
-                        undefined
-                      ];
+              switch (dir) {
+                case /* North */0 :
+                case /* South */1 :
+                    collide_block(undefined, dir, o2$7);
+                    return [
+                            undefined,
+                            undefined
+                          ];
+                case /* East */2 :
+                case /* West */3 :
+                    reverse_left_right(o2$7);
+                    return [
+                            undefined,
+                            undefined
+                          ];
+                
               }
           
         }
@@ -1918,81 +2021,96 @@ function process_collision(dir, c1, c2, state) {
         o1.invuln = 10;
         o1.jumping = false;
         o1.grounded = true;
-        if (typ >= 3) {
-          var r2 = evolve_enemy(o1.dir, typ, s2, o2, context);
-          o1.vel.y = - 4;
-          o1.pos.y = o1.pos.y - 5;
-          return [
-                  undefined,
-                  r2
-                ];
+        switch (typ) {
+          case /* GKoopaShell */3 :
+          case /* RKoopaShell */4 :
+              break;
+          default:
+            dec_health(o2);
+            o1.vel.y = - 4;
+            if (state.multiplier === 8) {
+              update_score(state, 800);
+              o2.score = 800;
+              return [
+                      undefined,
+                      evolve_enemy(o1.dir, typ, s2, o2, context)
+                    ];
+            }
+            var score = Math.imul(100, state.multiplier);
+            update_score(state, score);
+            o2.score = score;
+            state.multiplier = (state.multiplier << 1);
+            return [
+                    undefined,
+                    evolve_enemy(o1.dir, typ, s2, o2, context)
+                  ];
         }
-        dec_health(o2);
+        var r2 = evolve_enemy(o1.dir, typ, s2, o2, context);
         o1.vel.y = - 4;
-        if (state.multiplier === 8) {
-          update_score(state, 800);
-          o2.score = 800;
-          return [
-                  undefined,
-                  evolve_enemy(o1.dir, typ, s2, o2, context)
-                ];
-        }
-        var score = Math.imul(100, state.multiplier);
-        update_score(state, score);
-        o2.score = score;
-        state.multiplier = (state.multiplier << 1);
+        o1.pos.y = o1.pos.y - 5;
         return [
                 undefined,
-                evolve_enemy(o1.dir, typ, s2, o2, context)
+                r2
               ];
     case 2 :
-        if (t2 >= 3) {
-          var r2$1 = o2$1.vel.x === 0 ? evolve_enemy(o1$1.dir, t2, s2$1, o2$1, context) : (dec_health(o1$1), o1$1.invuln = 60, undefined);
-          return [
-                  undefined,
-                  r2$1
-                ];
+        switch (t2) {
+          case /* GKoopaShell */3 :
+          case /* RKoopaShell */4 :
+              break;
+          default:
+            dec_health(o1$1);
+            o1$1.invuln = 60;
+            return [
+                    undefined,
+                    undefined
+                  ];
         }
-        dec_health(o1$1);
-        o1$1.invuln = 60;
+        var r2$1 = o2$1.vel.x === 0 ? evolve_enemy(o1$1.dir, t2, s2$1, o2$1, context) : (dec_health(o1$1), o1$1.invuln = 60, undefined);
         return [
                 undefined,
-                undefined
+                r2$1
               ];
     case 3 :
-        if (t2$1 !== 0) {
-          if (t2$1 >= 3) {
-            state.coins = state.coins + 1 | 0;
-            dec_health(o2$2);
-            update_score(state, 100);
-            return [
-                    undefined,
-                    undefined
-                  ];
-          } else {
-            dec_health(o2$2);
-            update_score(state, 1000);
-            return [
-                    undefined,
-                    undefined
-                  ];
-          }
-        } else {
+        var exit$6 = 0;
+        switch (t2$1) {
+          case /* Mushroom */0 :
+              dec_health(o2$2);
+              if (o1$2.health === 2) {
+                
+              } else {
+                o1$2.health = o1$2.health + 1 | 0;
+              }
+              o1$2.vel.x = 0;
+              o1$2.vel.y = 0;
+              update_score(state, 1000);
+              o2$2.score = 1000;
+              return [
+                      undefined,
+                      undefined
+                    ];
+          case /* FireFlower */1 :
+          case /* Star */2 :
+              exit$6 = 4;
+              break;
+          case /* Coin */3 :
+              state.coins = state.coins + 1 | 0;
+              dec_health(o2$2);
+              update_score(state, 100);
+              return [
+                      undefined,
+                      undefined
+                    ];
+          
+        }
+        if (exit$6 === 4) {
           dec_health(o2$2);
-          if (o1$2.health === 2) {
-            
-          } else {
-            o1$2.health = o1$2.health + 1 | 0;
-          }
-          o1$2.vel.x = 0;
-          o1$2.vel.y = 0;
           update_score(state, 1000);
-          o2$2.score = 1000;
           return [
                   undefined,
                   undefined
                 ];
         }
+        break;
     
   }
 }
diff --git a/jscomp/test/ocaml_re_test.js b/jscomp/test/ocaml_re_test.js
index ac6b046708..78a774aab5 100644
--- a/jscomp/test/ocaml_re_test.js
+++ b/jscomp/test/ocaml_re_test.js
@@ -293,10 +293,10 @@ function compare(param, param$1) {
 }
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -313,26 +313,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -348,23 +350,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -373,7 +375,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -483,16 +485,18 @@ function from_char(param) {
 }
 
 function height$1(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create$1(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -502,25 +506,27 @@ function create$1(l, v, r) {
 }
 
 function bal$1(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height$1(ll) >= height$1(lr)) {
-        return create$1(ll, lv, create$1(lr, v, r));
-      }
-      if (lr) {
-        return create$1(create$1(ll, lv, lr.l), lr.v, create$1(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height$1(ll) >= height$1(lr)) {
+      return create$1(ll, lv, create$1(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create$1(create$1(ll, lv, lr.l), lr.v, create$1(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -535,22 +541,22 @@ function bal$1(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height$1(rr) >= height$1(rl)) {
-      return create$1(create$1(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create$1(create$1(l, v, rl.l), rl.v, create$1(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height$1(rr) >= height$1(rl)) {
+    return create$1(create$1(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create$1(create$1(l, v, rl.l), rl.v, create$1(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -559,7 +565,7 @@ function bal$1(l, v, r) {
 }
 
 function add$1(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -704,7 +710,7 @@ function seq$1(ids, kind, x, y) {
   var match = x.def;
   var match$1 = y.def;
   var exit = 0;
-  if (typeof match === "number") {
+  if (/* tag */typeof match === "number") {
     return y;
   }
   if (match.TAG === /* Alt */1) {
@@ -716,7 +722,7 @@ function seq$1(ids, kind, x, y) {
     exit = 2;
   }
   if (exit === 2) {
-    if (typeof match$1 === "number") {
+    if (/* tag */typeof match$1 === "number") {
       if (kind === "First") {
         return x;
       }
@@ -736,7 +742,7 @@ function seq$1(ids, kind, x, y) {
 
 function is_eps(expr) {
   var match = expr.def;
-  if (typeof match === "number") {
+  if (/* tag */typeof match === "number") {
     return true;
   } else {
     return false;
@@ -762,7 +768,7 @@ function erase(ids, m, m$p) {
 
 function rename(ids, x) {
   var l = x.def;
-  if (typeof l === "number") {
+  if (/* tag */typeof l === "number") {
     return mk_expr(ids, x.def);
   }
   switch (l.TAG | 0) {
@@ -903,7 +909,8 @@ function tseq(kind, x, y, rem) {
   var match = x.hd;
   switch (match.TAG | 0) {
     case /* TExp */1 :
-        if (typeof match._1.def === "number" && !x.tl) {
+        var tmp = match._1.def;
+        if (/* tag */typeof tmp === "number" && !x.tl) {
           return {
                   hd: {
                     TAG: /* TExp */1,
@@ -1097,7 +1104,8 @@ function remove_duplicates(prev, _l, y) {
                 ];
       case /* TExp */1 :
           var x$2 = x._1;
-          if (typeof x$2.def === "number") {
+          var tmp = x$2.def;
+          if (/* tag */typeof tmp === "number") {
             var r = l.tl;
             if (List.memq(y.id, prev)) {
               _l = r;
@@ -1197,7 +1205,7 @@ function filter_marks(b, e, marks) {
 
 function delta_1(marks, c, next_cat, prev_cat, x, rem) {
   var s = x.def;
-  if (typeof s === "number") {
+  if (/* tag */typeof s === "number") {
     return {
             hd: {
               TAG: /* TMatch */2,
@@ -1490,7 +1498,8 @@ var unknown_state = {
 
 function mk_state(ncol, desc) {
   var match = status(desc);
-  var break_state = typeof match === "number" ? match === 0 : true;
+  var break_state;
+  break_state = /* tag */typeof match === "number" && match !== /* Failed */0 ? false : true;
   return {
           idx: break_state ? -3 : desc.idx,
           real_idx: desc.idx,
@@ -1715,18 +1724,18 @@ function trans_set(cache, cm, s) {
     var _param = cache.contents;
     while(true) {
       var param = _param;
-      if (param) {
-        var c = compare(v, param.v);
-        if (c === 0) {
-          return param.d;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = compare(v, param.v);
+      if (c === 0) {
+        return param.d;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   }
   catch (raw_exn){
@@ -1745,7 +1754,7 @@ function trans_set(cache, cm, s) {
 function is_charset(_param) {
   while(true) {
     var param = _param;
-    if (typeof param === "number") {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     switch (param.TAG | 0) {
@@ -1834,7 +1843,7 @@ function colorize(c, regexp) {
   var colorize$1 = function (_regexp) {
     while(true) {
       var regexp = _regexp;
-      if (typeof regexp === "number") {
+      if (/* tag */typeof regexp === "number") {
         switch (regexp) {
           case /* Beg_of_line */0 :
           case /* End_of_line */1 :
@@ -1919,29 +1928,65 @@ function equal$2(_x1, _x2) {
   while(true) {
     var x2 = _x2;
     var x1 = _x1;
-    if (typeof x1 === "number") {
+    if (/* tag */typeof x1 === "number") {
       switch (x1) {
         case /* Beg_of_line */0 :
-            return x2 === 0;
+            if (/* tag */typeof x2 === "number" && x2 === /* Beg_of_line */0) {
+              return true;
+            } else {
+              return false;
+            }
         case /* End_of_line */1 :
-            return x2 === 1;
+            if (/* tag */typeof x2 === "number" && x2 === /* End_of_line */1) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Beg_of_word */2 :
-            return x2 === 2;
+            if (/* tag */typeof x2 === "number" && x2 === /* Beg_of_word */2) {
+              return true;
+            } else {
+              return false;
+            }
         case /* End_of_word */3 :
-            return x2 === 3;
+            if (/* tag */typeof x2 === "number" && x2 === /* End_of_word */3) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Not_bound */4 :
-            return x2 === 4;
+            if (/* tag */typeof x2 === "number" && x2 === /* Not_bound */4) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Beg_of_str */5 :
-            return x2 === 5;
+            if (/* tag */typeof x2 === "number" && x2 === /* Beg_of_str */5) {
+              return true;
+            } else {
+              return false;
+            }
         case /* End_of_str */6 :
-            return x2 === 6;
+            if (/* tag */typeof x2 === "number" && x2 === /* End_of_str */6) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Last_end_of_line */7 :
-            return x2 === 7;
+            if (/* tag */typeof x2 === "number" && x2 === /* Last_end_of_line */7) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Start */8 :
-            return x2 === 8;
+            if (/* tag */typeof x2 === "number" && x2 === /* Start */8) {
+              return true;
+            } else {
+              return false;
+            }
         case /* Stop */9 :
-            if (typeof x2 === "number") {
-              return x2 >= 9;
+            if (/* tag */typeof x2 === "number" && x2 === /* Stop */9) {
+              return true;
             } else {
               return false;
             }
@@ -1950,25 +1995,25 @@ function equal$2(_x1, _x2) {
     } else {
       switch (x1.TAG | 0) {
         case /* Set */0 :
-            if (typeof x2 === "number" || x2.TAG !== /* Set */0) {
+            if (/* tag */typeof x2 === "number" || x2.TAG !== /* Set */0) {
               return false;
             } else {
               return Caml_obj.equal(x1._0, x2._0);
             }
         case /* Sequence */1 :
-            if (typeof x2 === "number" || x2.TAG !== /* Sequence */1) {
+            if (/* tag */typeof x2 === "number" || x2.TAG !== /* Sequence */1) {
               return false;
             } else {
               return eq_list(x1._0, x2._0);
             }
         case /* Alternative */2 :
-            if (typeof x2 === "number" || x2.TAG !== /* Alternative */2) {
+            if (/* tag */typeof x2 === "number" || x2.TAG !== /* Alternative */2) {
               return false;
             } else {
               return eq_list(x1._0, x2._0);
             }
         case /* Repeat */3 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Repeat */3) {
@@ -1984,7 +2029,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._0;
             continue ;
         case /* Sem */4 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Sem */4) {
@@ -1997,7 +2042,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._1;
             continue ;
         case /* Sem_greedy */5 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Sem_greedy */5) {
@@ -2012,7 +2057,7 @@ function equal$2(_x1, _x2) {
         case /* Group */6 :
             return false;
         case /* No_group */7 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* No_group */7) {
@@ -2022,7 +2067,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._0;
             continue ;
         case /* Nest */8 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Nest */8) {
@@ -2032,7 +2077,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._0;
             continue ;
         case /* Case */9 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Case */9) {
@@ -2042,7 +2087,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._0;
             continue ;
         case /* No_case */10 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* No_case */10) {
@@ -2052,19 +2097,19 @@ function equal$2(_x1, _x2) {
             _x1 = x1._0;
             continue ;
         case /* Intersection */11 :
-            if (typeof x2 === "number" || x2.TAG !== /* Intersection */11) {
+            if (/* tag */typeof x2 === "number" || x2.TAG !== /* Intersection */11) {
               return false;
             } else {
               return eq_list(x1._0, x2._0);
             }
         case /* Complement */12 :
-            if (typeof x2 === "number" || x2.TAG !== /* Complement */12) {
+            if (/* tag */typeof x2 === "number" || x2.TAG !== /* Complement */12) {
               return false;
             } else {
               return eq_list(x1._0, x2._0);
             }
         case /* Difference */13 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Difference */13) {
@@ -2077,7 +2122,7 @@ function equal$2(_x1, _x2) {
             _x1 = x1._1;
             continue ;
         case /* Pmark */14 :
-            if (typeof x2 === "number") {
+            if (/* tag */typeof x2 === "number") {
               return false;
             }
             if (x2.TAG !== /* Pmark */14) {
@@ -2136,7 +2181,7 @@ function merge_sequences(_param) {
       return /* [] */0;
     }
     var l$p = param.hd;
-    if (typeof l$p !== "number") {
+    if (/* tag */typeof l$p !== "number") {
       switch (l$p.TAG | 0) {
         case /* Sequence */1 :
             var match = l$p._0;
@@ -2147,7 +2192,7 @@ function merge_sequences(_param) {
               var exit = 0;
               if (r$p) {
                 var match$1 = r$p.hd;
-                if (typeof match$1 === "number" || match$1.TAG !== /* Sequence */1) {
+                if (/* tag */typeof match$1 === "number" || match$1.TAG !== /* Sequence */1) {
                   exit = 2;
                 } else {
                   var match$2 = match$1._0;
@@ -2226,7 +2271,7 @@ function translate(ids, kind, _ign_group, ign_case, _greedy, pos, cache, c, _s)
     var s = _s;
     var greedy = _greedy;
     var ign_group = _ign_group;
-    if (typeof s === "number") {
+    if (/* tag */typeof s === "number") {
       switch (s) {
         case /* Beg_of_line */0 :
             var c$1 = Curry._2(Re_automata_Category.$plus$plus, Re_automata_Category.inexistant, Re_automata_Category.newline);
@@ -2511,7 +2556,7 @@ function case_insens(s) {
 }
 
 function as_set(s) {
-  if (typeof s === "number") {
+  if (/* tag */typeof s === "number") {
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
@@ -2540,7 +2585,7 @@ function handle_case(_ign_case, _s) {
   while(true) {
     var s = _s;
     var ign_case = _ign_case;
-    if (typeof s === "number") {
+    if (/* tag */typeof s === "number") {
       return s;
     }
     switch (s.TAG | 0) {
@@ -2686,7 +2731,7 @@ function handle_case(_ign_case, _s) {
 function anchored(_l) {
   while(true) {
     var l = _l;
-    if (typeof l === "number") {
+    if (/* tag */typeof l === "number") {
       switch (l) {
         case /* Beg_of_str */5 :
         case /* Start */8 :
@@ -3196,11 +3241,11 @@ function exec_internal(name, posOpt, lenOpt, groups, re, s) {
     }
     res = match[1];
   }
-  if (typeof res === "number") {
-    if (res !== 0) {
-      return /* Running */1;
-    } else {
+  if (/* tag */typeof res === "number") {
+    if (res === /* Failed */0) {
       return /* Failed */0;
+    } else {
+      return /* Running */1;
     }
   } else {
     return /* Match */{
@@ -4149,13 +4194,19 @@ function re(flagsOpt, pat) {
 function exec(rex, pos, s) {
   var len;
   var substr = exec_internal("Re.exec", pos, len, true, rex, s);
-  if (typeof substr === "number") {
+  if (/* tag */typeof substr !== "number") {
+    return substr._0;
+  }
+  if (substr === /* Failed */0) {
     throw {
           RE_EXN_ID: "Not_found",
           Error: new Error()
         };
   }
-  return substr._0;
+  throw {
+        RE_EXN_ID: "Not_found",
+        Error: new Error()
+      };
 }
 
 var s = "a".repeat(1048575) + "b";
diff --git a/jscomp/test/offset.js b/jscomp/test/offset.js
index df5f481168..ad1a539c54 100644
--- a/jscomp/test/offset.js
+++ b/jscomp/test/offset.js
@@ -7,16 +7,18 @@ var $$String = require("../../lib/js/string.js");
 var Caml_option = require("../../lib/js/caml_option.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -26,25 +28,27 @@ function create(l, v, r) {
 }
 
 function bal(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, create(lr, v, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, create(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -59,22 +63,22 @@ function bal(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -83,7 +87,7 @@ function bal(l, v, r) {
 }
 
 function add(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -124,30 +128,30 @@ function singleton(x) {
 }
 
 function add_min_element(x, param) {
-  if (param) {
-    return bal(add_min_element(x, param.l), param.v, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(add_min_element(x, param.l), param.v, param.r);
   }
 }
 
 function add_max_element(x, param) {
-  if (param) {
-    return bal(param.l, param.v, add_max_element(x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(param.l, param.v, add_max_element(x, param.r));
   }
 }
 
 function join(l, v, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_element(v, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_element(v, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, join(l.r, v, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -160,29 +164,29 @@ function join(l, v, r) {
 function min_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return param.v;
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.v;
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return Caml_option.some(param.v);
     }
     _param = l;
@@ -193,29 +197,29 @@ function min_elt_opt(_param) {
 function max_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return param.v;
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return param.v;
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return Caml_option.some(param.v);
     }
     _param = r;
@@ -224,35 +228,33 @@ function max_elt_opt(_param) {
 }
 
 function remove_min_elt(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_elt(l), param.v, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Set.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_elt(l), param.v, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function concat(t1, t2) {
-  if (t1) {
-    if (t2) {
-      return join(t1, min_elt(t2), remove_min_elt(t2));
-    } else {
-      return t1;
-    }
-  } else {
+  if (/* tag */typeof t1 === "number") {
     return t2;
+  } else if (/* tag */typeof t2 === "number") {
+    return t1;
+  } else {
+    return join(t1, min_elt(t2), remove_min_elt(t2));
   }
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             false,
@@ -287,17 +289,17 @@ function split(x, param) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.string_compare(x, param.v);
@@ -310,7 +312,7 @@ function mem(x, _param) {
 }
 
 function remove(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -318,14 +320,12 @@ function remove(x, t) {
   var l = t.l;
   var c = Caml.string_compare(x, v);
   if (c === 0) {
-    if (l) {
-      if (r) {
-        return bal(l, min_elt(r), remove_min_elt(r));
-      } else {
-        return l;
-      }
-    } else {
+    if (/* tag */typeof l === "number") {
       return r;
+    } else if (/* tag */typeof r === "number") {
+      return l;
+    } else {
+      return bal(l, min_elt(r), remove_min_elt(r));
     }
   }
   if (c < 0) {
@@ -345,16 +345,16 @@ function remove(x, t) {
 }
 
 function union(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var h1 = s1.h;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var h2 = s2.h;
   var v2 = s2.v;
-  var h1 = s1.h;
-  var v1 = s1.v;
   if (h1 >= h2) {
     if (h2 === 1) {
       return add(v2, s1);
@@ -370,10 +370,10 @@ function union(s1, s2) {
 }
 
 function inter(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return /* Empty */0;
   }
   var r1 = s1.r;
@@ -389,10 +389,10 @@ function inter(s1, s2) {
 }
 
 function diff(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var r1 = s1.r;
@@ -411,7 +411,7 @@ function cons_enum(_s, _e) {
   while(true) {
     var e = _e;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return e;
     }
     _e = /* More */{
@@ -430,14 +430,14 @@ function compare(s1, s2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.string_compare(e1._0, e2._0);
@@ -458,17 +458,17 @@ function subset(_s1, _s2) {
   while(true) {
     var s2 = _s2;
     var s1 = _s1;
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return true;
     }
-    if (!s2) {
+    var r1 = s1.r;
+    var v1 = s1.v;
+    var l1 = s1.l;
+    if (/* tag */typeof s2 === "number") {
       return false;
     }
     var r2 = s2.r;
     var l2 = s2.l;
-    var r1 = s1.r;
-    var v1 = s1.v;
-    var l1 = s1.l;
     var c = Caml.string_compare(v1, s2.v);
     if (c === 0) {
       if (!subset(l1, l2)) {
@@ -506,7 +506,7 @@ function subset(_s1, _s2) {
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -520,7 +520,7 @@ function fold(f, _s, _accu) {
   while(true) {
     var accu = _accu;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return accu;
     }
     _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -532,7 +532,7 @@ function fold(f, _s, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._1(p, param.v)) {
@@ -549,7 +549,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._1(p, param.v)) {
@@ -564,7 +564,7 @@ function exists(p, _param) {
 }
 
 function filter(p, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -585,7 +585,7 @@ function filter(p, t) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -613,10 +613,10 @@ function partition(p, param) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -624,7 +624,7 @@ function elements_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
@@ -643,60 +643,60 @@ function elements(s) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      var c = Caml.string_compare(x, v);
-      if (c === 0) {
-        return v;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var v = param.v;
+    var c = Caml.string_compare(x, v);
+    if (c === 0) {
+      return v;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -706,7 +706,7 @@ function find_first_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -727,41 +727,41 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -771,7 +771,7 @@ function find_last_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -792,7 +792,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -806,7 +806,7 @@ function find_opt(x, _param) {
 }
 
 function map(f, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
diff --git a/jscomp/test/option_repr_test.js b/jscomp/test/option_repr_test.js
index 2bf9c4b47e..0f0510be1c 100644
--- a/jscomp/test/option_repr_test.js
+++ b/jscomp/test/option_repr_test.js
@@ -31,10 +31,10 @@ function f0(x) {
 }
 
 function f1(u) {
-  if (u) {
-    return 0;
-  } else {
+  if (/* tag */typeof u === "number") {
     return 1;
+  } else {
+    return 0;
   }
 }
 
diff --git a/jscomp/test/pq_test.js b/jscomp/test/pq_test.js
index 0da4bdfadb..7306823b14 100644
--- a/jscomp/test/pq_test.js
+++ b/jscomp/test/pq_test.js
@@ -3,7 +3,7 @@
 var Caml_exceptions = require("../../lib/js/caml_exceptions.js");
 
 function insert(queue, prio, elt) {
-  if (!queue) {
+  if (/* tag */typeof queue === "number") {
     return /* Node */{
             _0: prio,
             _1: elt,
@@ -35,41 +35,42 @@ function insert(queue, prio, elt) {
 var Queue_is_empty = /* @__PURE__ */Caml_exceptions.create("Pq_test.PrioQueue.Queue_is_empty");
 
 function remove_top(param) {
-  if (param) {
-    var left = param._2;
-    if (!param._3) {
-      return left;
-    }
-    if (!left) {
-      return param._3;
-    }
-    var right = param._3;
-    var rprio = right._0;
-    var lprio = left._0;
-    if (lprio <= rprio) {
-      return /* Node */{
-              _0: lprio,
-              _1: left._1,
-              _2: remove_top(left),
-              _3: right
-            };
-    } else {
-      return /* Node */{
-              _0: rprio,
-              _1: right._1,
-              _2: left,
-              _3: remove_top(right)
-            };
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: Queue_is_empty,
+          Error: new Error()
+        };
+  }
+  var left = param._2;
+  var tmp = param._3;
+  if (/* tag */typeof tmp === "number") {
+    return left;
+  }
+  if (/* tag */typeof left === "number") {
+    return param._3;
+  }
+  var right = param._3;
+  var rprio = right._0;
+  var lprio = left._0;
+  if (lprio <= rprio) {
+    return /* Node */{
+            _0: lprio,
+            _1: left._1,
+            _2: remove_top(left),
+            _3: right
+          };
+  } else {
+    return /* Node */{
+            _0: rprio,
+            _1: right._1,
+            _2: left,
+            _3: remove_top(right)
+          };
   }
-  throw {
-        RE_EXN_ID: Queue_is_empty,
-        Error: new Error()
-      };
 }
 
 function extract(queue) {
-  if (queue) {
+  if (/* tag */typeof queue !== "number") {
     return [
             queue._0,
             queue._1,
diff --git a/jscomp/test/rbset.js b/jscomp/test/rbset.js
index dc4cb0e87b..dff06c4c50 100644
--- a/jscomp/test/rbset.js
+++ b/jscomp/test/rbset.js
@@ -2,7 +2,12 @@
 
 
 function blackify(s) {
-  if (s && s._0) {
+  if (/* tag */typeof s === "number" || !s._0) {
+    return [
+            s,
+            true
+          ];
+  } else {
     return [
             /* Node */{
               _0: /* Black */0,
@@ -12,26 +17,21 @@ function blackify(s) {
             },
             false
           ];
-  } else {
-    return [
-            s,
-            true
-          ];
   }
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var y = param._2;
@@ -56,10 +56,14 @@ function balance_left(l, x, r) {
   var c;
   var z;
   var d;
-  if (l && l._0) {
+  if (/* tag */typeof l === "number" || !l._0) {
+    exit = 1;
+  } else {
     var a$1 = l._1;
     var exit$1 = 0;
-    if (a$1 && a$1._0) {
+    if (/* tag */typeof a$1 === "number" || !a$1._0) {
+      exit$1 = 3;
+    } else {
       a = a$1._1;
       x$1 = a$1._2;
       b = a$1._3;
@@ -68,12 +72,12 @@ function balance_left(l, x, r) {
       z = x;
       d = r;
       exit = 2;
-    } else {
-      exit$1 = 3;
     }
     if (exit$1 === 3) {
       var match = l._3;
-      if (match && match._0) {
+      if (/* tag */typeof match === "number" || !match._0) {
+        exit = 1;
+      } else {
         a = a$1;
         x$1 = l._2;
         b = match._1;
@@ -82,13 +86,9 @@ function balance_left(l, x, r) {
         z = x;
         d = r;
         exit = 2;
-      } else {
-        exit = 1;
       }
     }
     
-  } else {
-    exit = 1;
   }
   switch (exit) {
     case 1 :
@@ -128,10 +128,14 @@ function balance_right(l, x, r) {
   var c;
   var z;
   var d;
-  if (r && r._0) {
+  if (/* tag */typeof r === "number" || !r._0) {
+    exit = 1;
+  } else {
     var b$1 = r._1;
     var exit$1 = 0;
-    if (b$1 && b$1._0) {
+    if (/* tag */typeof b$1 === "number" || !b$1._0) {
+      exit$1 = 3;
+    } else {
       a = l;
       x$1 = x;
       b = b$1._1;
@@ -140,12 +144,12 @@ function balance_right(l, x, r) {
       z = r._2;
       d = r._3;
       exit = 2;
-    } else {
-      exit$1 = 3;
     }
     if (exit$1 === 3) {
       var match = r._3;
-      if (match && match._0) {
+      if (/* tag */typeof match === "number" || !match._0) {
+        exit = 1;
+      } else {
         a = l;
         x$1 = x;
         b = b$1;
@@ -154,13 +158,9 @@ function balance_right(l, x, r) {
         z = match._2;
         d = match._3;
         exit = 2;
-      } else {
-        exit = 1;
       }
     }
     
-  } else {
-    exit = 1;
   }
   switch (exit) {
     case 1 :
@@ -201,10 +201,10 @@ function singleton(x) {
 }
 
 function unbalanced_left(param) {
-  if (param) {
+  if (/* tag */typeof param !== "number") {
     if (param._0) {
       var match = param._1;
-      if (match && !match._0) {
+      if (/* tag */typeof match !== "number" && !match._0) {
         return [
                 balance_left(/* Node */{
                       _0: /* Red */1,
@@ -218,7 +218,7 @@ function unbalanced_left(param) {
       
     } else {
       var match$1 = param._1;
-      if (match$1) {
+      if (/* tag */typeof match$1 !== "number") {
         if (!match$1._0) {
           return [
                   balance_left(/* Node */{
@@ -231,7 +231,7 @@ function unbalanced_left(param) {
                 ];
         }
         var match$2 = match$1._3;
-        if (match$2 && !match$2._0) {
+        if (/* tag */typeof match$2 !== "number" && !match$2._0) {
           return [
                   /* Node */{
                     _0: /* Black */0,
@@ -264,10 +264,10 @@ function unbalanced_left(param) {
 }
 
 function unbalanced_right(param) {
-  if (param) {
+  if (/* tag */typeof param !== "number") {
     if (param._0) {
       var match = param._3;
-      if (match && !match._0) {
+      if (/* tag */typeof match !== "number" && !match._0) {
         return [
                 balance_right(param._1, param._2, /* Node */{
                       _0: /* Red */1,
@@ -281,9 +281,9 @@ function unbalanced_right(param) {
       
     } else {
       var match$1 = param._3;
-      if (match$1) {
-        var x = param._2;
-        var a = param._1;
+      var x = param._2;
+      var a = param._1;
+      if (/* tag */typeof match$1 !== "number") {
         if (!match$1._0) {
           return [
                   balance_right(a, x, /* Node */{
@@ -296,7 +296,7 @@ function unbalanced_right(param) {
                 ];
         }
         var match$2 = match$1._1;
-        if (match$2 && !match$2._0) {
+        if (/* tag */typeof match$2 !== "number" && !match$2._0) {
           return [
                   /* Node */{
                     _0: /* Black */0,
@@ -329,7 +329,7 @@ function unbalanced_right(param) {
 }
 
 function lbalance(x1, x2, x3) {
-  if (!x1) {
+  if (/* tag */typeof x1 === "number") {
     return /* Node */{
             _0: /* Black */0,
             _1: x1,
@@ -347,7 +347,7 @@ function lbalance(x1, x2, x3) {
   }
   var r = x1._3;
   var l = x1._1;
-  if (l && l._0) {
+  if (/* tag */typeof l !== "number" && l._0) {
     return /* Node */{
             _0: /* Red */1,
             _1: /* Node */{
@@ -365,7 +365,7 @@ function lbalance(x1, x2, x3) {
             }
           };
   }
-  if (!r) {
+  if (/* tag */typeof r === "number") {
     return /* Node */{
             _0: /* Black */0,
             _1: x1,
@@ -401,10 +401,12 @@ function lbalance(x1, x2, x3) {
 }
 
 function rbalance(x1, x2, x3) {
-  if (x3 && x3._0) {
+  if (/* tag */typeof x3 !== "number" && x3._0) {
     var b = x3._1;
     var exit = 0;
-    if (b) {
+    if (/* tag */typeof b === "number") {
+      exit = 2;
+    } else {
       if (b._0) {
         return /* Node */{
                 _0: /* Red */1,
@@ -424,12 +426,10 @@ function rbalance(x1, x2, x3) {
               };
       }
       exit = 2;
-    } else {
-      exit = 2;
     }
     if (exit === 2) {
       var match = x3._3;
-      if (match && match._0) {
+      if (/* tag */typeof match !== "number" && match._0) {
         return /* Node */{
                 _0: /* Red */1,
                 _1: /* Node */{
@@ -460,7 +460,7 @@ function rbalance(x1, x2, x3) {
 }
 
 function ins(x, s) {
-  if (!s) {
+  if (/* tag */typeof s === "number") {
     return /* Node */{
             _0: /* Red */1,
             _1: /* Empty */0,
@@ -506,34 +506,47 @@ function ins(x, s) {
 
 function add(x, s) {
   var s$1 = ins(x, s);
-  if (s$1 && s$1._0) {
+  if (/* tag */typeof s$1 === "number" || !s$1._0) {
+    return s$1;
+  } else {
     return /* Node */{
             _0: /* Black */0,
             _1: s$1._1,
             _2: s$1._2,
             _3: s$1._3
           };
-  } else {
-    return s$1;
   }
 }
 
 function remove_min(param) {
-  if (param) {
-    var c = param._0;
-    if (c) {
-      if (!param._1) {
-        return [
-                param._3,
-                param._2,
-                false
-              ];
-      }
-      
-    } else if (!param._1) {
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "rbset.ml",
+            115,
+            4
+          ],
+          Error: new Error()
+        };
+  }
+  var c = param._0;
+  if (c) {
+    var tmp = param._1;
+    if (/* tag */typeof tmp === "number") {
+      return [
+              param._3,
+              param._2,
+              false
+            ];
+    }
+    
+  } else {
+    var tmp$1 = param._1;
+    if (/* tag */typeof tmp$1 === "number") {
       var match = param._3;
       var x = param._2;
-      if (!match) {
+      if (/* tag */typeof match === "number") {
         return [
                 /* Empty */0,
                 x,
@@ -562,44 +575,36 @@ function remove_min(param) {
             Error: new Error()
           };
     }
-    var match$1 = remove_min(param._1);
-    var y = match$1[1];
-    var s_1 = match$1[0];
-    var s_2 = param._2;
-    var s_3 = param._3;
-    var s = /* Node */{
-      _0: c,
-      _1: s_1,
-      _2: s_2,
-      _3: s_3
-    };
-    if (!match$1[2]) {
-      return [
-              s,
-              y,
-              false
-            ];
-    }
-    var match$2 = unbalanced_right(s);
+    
+  }
+  var match$1 = remove_min(param._1);
+  var y = match$1[1];
+  var s_1 = match$1[0];
+  var s_2 = param._2;
+  var s_3 = param._3;
+  var s = /* Node */{
+    _0: c,
+    _1: s_1,
+    _2: s_2,
+    _3: s_3
+  };
+  if (!match$1[2]) {
     return [
-            match$2[0],
+            s,
             y,
-            match$2[1]
+            false
           ];
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "rbset.ml",
-          115,
-          4
-        ],
-        Error: new Error()
-      };
+  var match$2 = unbalanced_right(s);
+  return [
+          match$2[0],
+          y,
+          match$2[1]
+        ];
 }
 
 function remove_aux(x, n) {
-  if (!n) {
+  if (/* tag */typeof n === "number") {
     return [
             /* Empty */0,
             false
@@ -610,7 +615,7 @@ function remove_aux(x, n) {
   var l = n._1;
   var c = n._0;
   if (x === y) {
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       if (c === /* Red */1) {
         return [
                 l,
@@ -679,10 +684,10 @@ function remove(x, s) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (1 + cardinal(param._1) | 0) + cardinal(param._3) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (1 + cardinal(param._1) | 0) + cardinal(param._3) | 0;
   }
 }
 
diff --git a/jscomp/test/rec_module_test.js b/jscomp/test/rec_module_test.js
index d44f69842f..589aa443a4 100644
--- a/jscomp/test/rec_module_test.js
+++ b/jscomp/test/rec_module_test.js
@@ -95,16 +95,18 @@ var AAA = {
 };
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -114,25 +116,27 @@ function create(l, v, r) {
 }
 
 function bal(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, create(lr, v, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, create(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -147,22 +151,22 @@ function bal(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -171,7 +175,7 @@ function bal(l, v, r) {
 }
 
 function add(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -212,30 +216,30 @@ function singleton(x) {
 }
 
 function add_min_element(x, param) {
-  if (param) {
-    return bal(add_min_element(x, param.l), param.v, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(add_min_element(x, param.l), param.v, param.r);
   }
 }
 
 function add_max_element(x, param) {
-  if (param) {
-    return bal(param.l, param.v, add_max_element(x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(param.l, param.v, add_max_element(x, param.r));
   }
 }
 
 function join(l, v, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_element(v, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_element(v, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, join(l.r, v, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -248,29 +252,29 @@ function join(l, v, r) {
 function min_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return param.v;
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.v;
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return Caml_option.some(param.v);
     }
     _param = l;
@@ -281,29 +285,29 @@ function min_elt_opt(_param) {
 function max_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return param.v;
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return param.v;
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return Caml_option.some(param.v);
     }
     _param = r;
@@ -312,35 +316,33 @@ function max_elt_opt(_param) {
 }
 
 function remove_min_elt(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_elt(l), param.v, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Set.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_elt(l), param.v, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function concat(t1, t2) {
-  if (t1) {
-    if (t2) {
-      return join(t1, min_elt(t2), remove_min_elt(t2));
-    } else {
-      return t1;
-    }
-  } else {
+  if (/* tag */typeof t1 === "number") {
     return t2;
+  } else if (/* tag */typeof t2 === "number") {
+    return t1;
+  } else {
+    return join(t1, min_elt(t2), remove_min_elt(t2));
   }
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             false,
@@ -375,17 +377,17 @@ function split(x, param) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Curry._2(AAA.compare, x, param.v);
@@ -398,7 +400,7 @@ function mem(x, _param) {
 }
 
 function remove(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -406,14 +408,12 @@ function remove(x, t) {
   var l = t.l;
   var c = Curry._2(AAA.compare, x, v);
   if (c === 0) {
-    if (l) {
-      if (r) {
-        return bal(l, min_elt(r), remove_min_elt(r));
-      } else {
-        return l;
-      }
-    } else {
+    if (/* tag */typeof l === "number") {
       return r;
+    } else if (/* tag */typeof r === "number") {
+      return l;
+    } else {
+      return bal(l, min_elt(r), remove_min_elt(r));
     }
   }
   if (c < 0) {
@@ -433,16 +433,16 @@ function remove(x, t) {
 }
 
 function union(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var h1 = s1.h;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var h2 = s2.h;
   var v2 = s2.v;
-  var h1 = s1.h;
-  var v1 = s1.v;
   if (h1 >= h2) {
     if (h2 === 1) {
       return add(v2, s1);
@@ -458,10 +458,10 @@ function union(s1, s2) {
 }
 
 function inter(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return /* Empty */0;
   }
   var r1 = s1.r;
@@ -477,10 +477,10 @@ function inter(s1, s2) {
 }
 
 function diff(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var r1 = s1.r;
@@ -499,7 +499,7 @@ function cons_enum(_s, _e) {
   while(true) {
     var e = _e;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return e;
     }
     _e = /* More */{
@@ -518,14 +518,14 @@ function compare$1(s1, s2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Curry._2(AAA.compare, e1._0, e2._0);
@@ -546,17 +546,17 @@ function subset(_s1, _s2) {
   while(true) {
     var s2 = _s2;
     var s1 = _s1;
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return true;
     }
-    if (!s2) {
+    var r1 = s1.r;
+    var v1 = s1.v;
+    var l1 = s1.l;
+    if (/* tag */typeof s2 === "number") {
       return false;
     }
     var r2 = s2.r;
     var l2 = s2.l;
-    var r1 = s1.r;
-    var v1 = s1.v;
-    var l1 = s1.l;
     var c = Curry._2(AAA.compare, v1, s2.v);
     if (c === 0) {
       if (!subset(l1, l2)) {
@@ -594,7 +594,7 @@ function subset(_s1, _s2) {
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -608,7 +608,7 @@ function fold(f, _s, _accu) {
   while(true) {
     var accu = _accu;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return accu;
     }
     _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -620,7 +620,7 @@ function fold(f, _s, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._1(p, param.v)) {
@@ -637,7 +637,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._1(p, param.v)) {
@@ -652,7 +652,7 @@ function exists(p, _param) {
 }
 
 function filter(p, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -673,7 +673,7 @@ function filter(p, t) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -701,10 +701,10 @@ function partition(p, param) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -712,7 +712,7 @@ function elements_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
@@ -731,60 +731,60 @@ function elements(s) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      var c = Curry._2(AAA.compare, x, v);
-      if (c === 0) {
-        return v;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var v = param.v;
+    var c = Curry._2(AAA.compare, x, v);
+    if (c === 0) {
+      return v;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -794,7 +794,7 @@ function find_first_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -815,41 +815,41 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -859,7 +859,7 @@ function find_last_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -880,7 +880,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -894,7 +894,7 @@ function find_opt(x, _param) {
 }
 
 function map(f, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
diff --git a/jscomp/test/record_extension_test.js b/jscomp/test/record_extension_test.js
index d04c826d77..7acc8f379b 100644
--- a/jscomp/test/record_extension_test.js
+++ b/jscomp/test/record_extension_test.js
@@ -36,7 +36,7 @@ var v0 = {
 eq("File \"record_extension_test.ml\", line 19, characters 6-13", f(v0), 7);
 
 function f2(x) {
-  if (typeof x === "number" || x.TAG !== /* C */0) {
+  if (/* tag */typeof x === "number" || x.TAG !== /* C */0) {
     return 0;
   } else {
     return x.x;
@@ -44,7 +44,7 @@ function f2(x) {
 }
 
 function f2_with(x) {
-  if (typeof x === "number" || x.TAG !== /* C */0) {
+  if (/* tag */typeof x === "number" || x.TAG !== /* C */0) {
     return x;
   } else {
     return {
diff --git a/jscomp/test/recursive_records_test.js b/jscomp/test/recursive_records_test.js
index 15705657ec..56f8db5da7 100644
--- a/jscomp/test/recursive_records_test.js
+++ b/jscomp/test/recursive_records_test.js
@@ -55,15 +55,15 @@ function f2(x) {
 }
 
 function hd(x) {
-  if (x) {
-    return x.content;
-  } else {
+  if (/* tag */typeof x === "number") {
     return 0;
+  } else {
+    return x.content;
   }
 }
 
 function tl_exn(x) {
-  if (x) {
+  if (/* tag */typeof x !== "number") {
     return x.next;
   }
   throw {
diff --git a/jscomp/test/set_gen.js b/jscomp/test/set_gen.js
index 41a01e95d4..6956bad202 100644
--- a/jscomp/test/set_gen.js
+++ b/jscomp/test/set_gen.js
@@ -9,7 +9,7 @@ function cons_enum(_s, _e) {
   while(true) {
     var e = _e;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return e;
     }
     _e = /* More */{
@@ -23,54 +23,54 @@ function cons_enum(_s, _e) {
 }
 
 function height(param) {
-  if (param) {
-    return param._3;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param._3;
   }
 }
 
 function min_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param._0;
-      if (!l) {
-        return param._1;
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param._0;
+    if (/* tag */typeof l === "number") {
+      return param._1;
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function max_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param._2;
-      if (!r) {
-        return param._1;
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param._2;
+    if (/* tag */typeof r === "number") {
+      return param._1;
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
@@ -78,7 +78,7 @@ function cardinal_aux(_acc, _param) {
   while(true) {
     var param = _param;
     var acc = _acc;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return acc;
     }
     _param = param._0;
@@ -95,7 +95,7 @@ function elements_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param._0;
@@ -114,7 +114,7 @@ function elements(s) {
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param._0);
@@ -128,7 +128,7 @@ function fold(f, _s, _accu) {
   while(true) {
     var accu = _accu;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return accu;
     }
     _accu = Curry._2(f, s._1, fold(f, s._0, accu));
@@ -140,7 +140,7 @@ function fold(f, _s, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._1(p, param._1)) {
@@ -157,7 +157,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._1(p, param._1)) {
@@ -198,7 +198,7 @@ var Height_invariant_broken = /* @__PURE__ */Caml_exceptions.create("Set_gen.Hei
 var Height_diff_borken = /* @__PURE__ */Caml_exceptions.create("Set_gen.Height_diff_borken");
 
 function check_height_and_diff(param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return 0;
   }
   var h = param._3;
@@ -225,8 +225,10 @@ function check(tree) {
 }
 
 function create(l, v, r) {
-  var hl = l ? l._3 : 0;
-  var hr = r ? r._3 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._3;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._3;
   return /* Node */{
           _0: l,
           _1: v,
@@ -236,35 +238,37 @@ function create(l, v, r) {
 }
 
 function internal_bal(l, v, r) {
-  var hl = l ? l._3 : 0;
-  var hr = r ? r._3 : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l._3;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r._3;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l._2;
-      var lv = l._1;
-      var ll = l._0;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, create(lr, v, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Assert_failure",
             _1: [
               "set_gen.ml",
-              235,
-              19
+              225,
+              15
             ],
             Error: new Error()
           };
     }
+    var lr = l._2;
+    var lv = l._1;
+    var ll = l._0;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, create(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
+    }
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
             "set_gen.ml",
-            225,
-            15
+            235,
+            19
           ],
           Error: new Error()
         };
@@ -277,51 +281,51 @@ function internal_bal(l, v, r) {
             _3: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r._2;
-    var rv = r._1;
-    var rl = r._0;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
             "set_gen.ml",
-            251,
-            19
+            245,
+            15
           ],
           Error: new Error()
         };
   }
+  var rr = r._2;
+  var rv = r._1;
+  var rl = r._0;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Assert_failure",
         _1: [
           "set_gen.ml",
-          245,
-          15
+          251,
+          19
         ],
         Error: new Error()
       };
 }
 
 function remove_min_elt(param) {
-  if (param) {
-    var l = param._0;
-    if (l) {
-      return internal_bal(remove_min_elt(l), param._1, param._2);
-    } else {
-      return param._2;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Set.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param._0;
+  if (/* tag */typeof l === "number") {
+    return param._2;
+  } else {
+    return internal_bal(remove_min_elt(l), param._1, param._2);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function singleton(x) {
@@ -334,42 +338,40 @@ function singleton(x) {
 }
 
 function internal_merge(l, r) {
-  if (l) {
-    if (r) {
-      return internal_bal(l, min_elt(r), remove_min_elt(r));
-    } else {
-      return l;
-    }
-  } else {
+  if (/* tag */typeof l === "number") {
     return r;
+  } else if (/* tag */typeof r === "number") {
+    return l;
+  } else {
+    return internal_bal(l, min_elt(r), remove_min_elt(r));
   }
 }
 
 function add_min_element(v, param) {
-  if (param) {
-    return internal_bal(add_min_element(v, param._0), param._1, param._2);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(v);
+  } else {
+    return internal_bal(add_min_element(v, param._0), param._1, param._2);
   }
 }
 
 function add_max_element(v, param) {
-  if (param) {
-    return internal_bal(param._0, param._1, add_max_element(v, param._2));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(v);
+  } else {
+    return internal_bal(param._0, param._1, add_max_element(v, param._2));
   }
 }
 
 function internal_join(l, v, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_element(v, r);
   }
-  if (!r) {
+  var lh = l._3;
+  if (/* tag */typeof r === "number") {
     return add_max_element(v, l);
   }
   var rh = r._3;
-  var lh = l._3;
   if (lh > (rh + 2 | 0)) {
     return internal_bal(l._0, l._1, internal_join(l._2, v, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -380,19 +382,17 @@ function internal_join(l, v, r) {
 }
 
 function internal_concat(t1, t2) {
-  if (t1) {
-    if (t2) {
-      return internal_join(t1, min_elt(t2), remove_min_elt(t2));
-    } else {
-      return t1;
-    }
-  } else {
+  if (/* tag */typeof t1 === "number") {
     return t2;
+  } else if (/* tag */typeof t2 === "number") {
+    return t1;
+  } else {
+    return internal_join(t1, min_elt(t2), remove_min_elt(t2));
   }
 }
 
 function filter(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param._1;
@@ -407,7 +407,7 @@ function filter(p, param) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -596,7 +596,7 @@ function of_sorted_array(l) {
 
 function is_ordered(cmp, tree) {
   var is_ordered_min_max = function (tree) {
-    if (!tree) {
+    if (/* tag */typeof tree === "number") {
       return "Empty";
     }
     var r = tree._2;
@@ -675,14 +675,14 @@ function compare_aux(cmp, _e1, _e2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Curry._2(cmp, e1._0, e2._0);
diff --git a/jscomp/test/simplify_lambda_632o.js b/jscomp/test/simplify_lambda_632o.js
index 1a43d21472..e9b3d731e0 100644
--- a/jscomp/test/simplify_lambda_632o.js
+++ b/jscomp/test/simplify_lambda_632o.js
@@ -2,11 +2,31 @@
 
 
 function f(x) {
-  return x;
+  switch (x) {
+    case /* X1 */0 :
+        return /* X1 */0;
+    case /* X2 */1 :
+        return /* X2 */1;
+    case /* X3 */2 :
+        return /* X3 */2;
+    case /* X4 */3 :
+        return /* X4 */3;
+    
+  }
 }
 
 function f2(x) {
-  return x;
+  switch (x) {
+    case /* X1 */0 :
+        return /* X1 */0;
+    case /* X2 */1 :
+        return /* X2 */1;
+    case /* X3 */2 :
+        return /* X3 */2;
+    case /* X4 */3 :
+        return /* X4 */3;
+    
+  }
 }
 
 exports.f = f;
diff --git a/jscomp/test/string_set.js b/jscomp/test/string_set.js
index a1d9eaba56..0e9cf8625d 100644
--- a/jscomp/test/string_set.js
+++ b/jscomp/test/string_set.js
@@ -7,7 +7,7 @@ var $$String = require("../../lib/js/string.js");
 var Set_gen = require("./set_gen.js");
 
 function split(x, tree) {
-  if (!tree) {
+  if (/* tag */typeof tree === "number") {
     return [
             /* Empty */0,
             false,
@@ -42,7 +42,7 @@ function split(x, tree) {
 }
 
 function add(x, tree) {
-  if (!tree) {
+  if (/* tag */typeof tree === "number") {
     return /* Node */{
             _0: /* Empty */0,
             _1: x,
@@ -64,16 +64,16 @@ function add(x, tree) {
 }
 
 function union(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var h1 = s1._3;
+  var v1 = s1._1;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var h2 = s2._3;
   var v2 = s2._1;
-  var h1 = s1._3;
-  var v1 = s1._1;
   if (h1 >= h2) {
     if (h2 === 1) {
       return add(v2, s1);
@@ -89,10 +89,10 @@ function union(s1, s2) {
 }
 
 function inter(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return /* Empty */0;
   }
   var r1 = s1._2;
@@ -108,10 +108,10 @@ function inter(s1, s2) {
 }
 
 function diff(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var r1 = s1._2;
@@ -129,7 +129,7 @@ function diff(s1, s2) {
 function mem(x, _tree) {
   while(true) {
     var tree = _tree;
-    if (!tree) {
+    if (/* tag */typeof tree === "number") {
       return false;
     }
     var c = Caml.string_compare(x, tree._1);
@@ -142,7 +142,7 @@ function mem(x, _tree) {
 }
 
 function remove(x, tree) {
-  if (!tree) {
+  if (/* tag */typeof tree === "number") {
     return /* Empty */0;
   }
   var r = tree._2;
@@ -170,17 +170,17 @@ function subset(_s1, _s2) {
   while(true) {
     var s2 = _s2;
     var s1 = _s1;
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return true;
     }
-    if (!s2) {
+    var r1 = s1._2;
+    var v1 = s1._1;
+    var l1 = s1._0;
+    if (/* tag */typeof s2 === "number") {
       return false;
     }
     var r2 = s2._2;
     var l2 = s2._0;
-    var r1 = s1._2;
-    var v1 = s1._1;
-    var l1 = s1._0;
     var c = Caml.string_compare(v1, s2._1);
     if (c === 0) {
       if (!subset(l1, l2)) {
@@ -218,19 +218,19 @@ function subset(_s1, _s2) {
 function find(x, _tree) {
   while(true) {
     var tree = _tree;
-    if (tree) {
-      var v = tree._1;
-      var c = Caml.string_compare(x, v);
-      if (c === 0) {
-        return v;
-      }
-      _tree = c < 0 ? tree._0 : tree._2;
-      continue ;
+    if (/* tag */typeof tree === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var v = tree._1;
+    var c = Caml.string_compare(x, v);
+    if (c === 0) {
+      return v;
+    }
+    _tree = c < 0 ? tree._0 : tree._2;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/test_demo.js b/jscomp/test/test_demo.js
index 5ffac0bb6a..46aad5cdc6 100644
--- a/jscomp/test/test_demo.js
+++ b/jscomp/test/test_demo.js
@@ -19,13 +19,13 @@ function cons(x, y) {
 }
 
 function map(f, param) {
-  if (param) {
+  if (/* tag */typeof param === "number") {
+    return /* Nil */0;
+  } else {
     return /* Cons */{
             _0: Curry._1(f, param._0),
             _1: map(f, param._1)
           };
-  } else {
-    return /* Nil */0;
   }
 }
 
diff --git a/jscomp/test/test_fib.js b/jscomp/test/test_fib.js
index 8a8cf14a09..0864c4aea6 100644
--- a/jscomp/test/test_fib.js
+++ b/jscomp/test/test_fib.js
@@ -42,21 +42,21 @@ function cons(x, y) {
 }
 
 function length(x) {
-  if (x) {
-    return 1 + length(x._1) | 0;
-  } else {
+  if (/* tag */typeof x === "number") {
     return 0;
+  } else {
+    return 1 + length(x._1) | 0;
   }
 }
 
 function map(f, x) {
-  if (x) {
+  if (/* tag */typeof x === "number") {
+    return /* Nil */0;
+  } else {
     return /* Cons */{
             _0: Curry._1(f, x._0),
             _1: map(f, x._1)
           };
-  } else {
-    return /* Nil */0;
   }
 }
 
diff --git a/jscomp/test/test_for_map.js b/jscomp/test/test_for_map.js
index 6766308a3d..c3d7508822 100644
--- a/jscomp/test/test_for_map.js
+++ b/jscomp/test/test_for_map.js
@@ -5,10 +5,10 @@ var Curry = require("../../lib/js/curry.js");
 var Caml_option = require("../../lib/js/caml_option.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -35,26 +35,28 @@ function singleton(x, d) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -70,23 +72,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -95,15 +97,15 @@ function bal(l, x, d, r) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -149,65 +151,65 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.int_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.int_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -219,7 +221,7 @@ function find_first_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -244,47 +246,47 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -296,7 +298,7 @@ function find_last_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -321,7 +323,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var c = Caml.int_compare(x, param.v);
@@ -336,7 +338,7 @@ function find_opt(x, _param) {
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.int_compare(x, param.v);
@@ -351,32 +353,32 @@ function mem(x, _param) {
 function min_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return [
               param.v,
               param.d
@@ -390,32 +392,32 @@ function min_binding_opt(_param) {
 function max_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return [
               param.v,
               param.d
@@ -427,26 +429,26 @@ function max_binding_opt(_param) {
 }
 
 function remove_min_binding(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_binding(l), param.v, param.d, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Map.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_binding(l), param.v, param.d, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function merge(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -454,7 +456,7 @@ function merge(t1, t2) {
 }
 
 function remove(x, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -482,63 +484,63 @@ function remove(x, m) {
 }
 
 function update(x, f, m) {
-  if (m) {
-    var r = m.r;
-    var d = m.d;
-    var v = m.v;
-    var l = m.l;
-    var c = Caml.int_compare(x, v);
-    if (c === 0) {
-      var data = Curry._1(f, Caml_option.some(d));
-      if (data === undefined) {
-        return merge(l, r);
-      }
-      var data$1 = Caml_option.valFromOption(data);
-      if (d === data$1) {
-        return m;
-      } else {
-        return /* Node */{
-                l: l,
-                v: x,
-                d: data$1,
-                r: r,
-                h: m.h
-              };
-      }
+  if (/* tag */typeof m === "number") {
+    var data = Curry._1(f, undefined);
+    if (data !== undefined) {
+      return /* Node */{
+              l: /* Empty */0,
+              v: x,
+              d: Caml_option.valFromOption(data),
+              r: /* Empty */0,
+              h: 1
+            };
+    } else {
+      return /* Empty */0;
     }
-    if (c < 0) {
-      var ll = update(x, f, l);
-      if (l === ll) {
-        return m;
-      } else {
-        return bal(ll, v, d, r);
-      }
+  }
+  var r = m.r;
+  var d = m.d;
+  var v = m.v;
+  var l = m.l;
+  var c = Caml.int_compare(x, v);
+  if (c === 0) {
+    var data$1 = Curry._1(f, Caml_option.some(d));
+    if (data$1 === undefined) {
+      return merge(l, r);
+    }
+    var data$2 = Caml_option.valFromOption(data$1);
+    if (d === data$2) {
+      return m;
+    } else {
+      return /* Node */{
+              l: l,
+              v: x,
+              d: data$2,
+              r: r,
+              h: m.h
+            };
     }
-    var rr = update(x, f, r);
-    if (r === rr) {
+  }
+  if (c < 0) {
+    var ll = update(x, f, l);
+    if (l === ll) {
       return m;
     } else {
-      return bal(l, v, d, rr);
+      return bal(ll, v, d, r);
     }
   }
-  var data$2 = Curry._1(f, undefined);
-  if (data$2 !== undefined) {
-    return /* Node */{
-            l: /* Empty */0,
-            v: x,
-            d: Caml_option.valFromOption(data$2),
-            r: /* Empty */0,
-            h: 1
-          };
+  var rr = update(x, f, r);
+  if (r === rr) {
+    return m;
   } else {
-    return /* Empty */0;
+    return bal(l, v, d, rr);
   }
 }
 
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -549,7 +551,7 @@ function iter(f, _param) {
 }
 
 function map(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var l$p = map(f, param.l);
@@ -565,7 +567,7 @@ function map(f, param) {
 }
 
 function mapi(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param.v;
@@ -585,7 +587,7 @@ function fold(f, _m, _accu) {
   while(true) {
     var accu = _accu;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return accu;
     }
     _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -597,7 +599,7 @@ function fold(f, _m, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._2(p, param.v, param.d)) {
@@ -614,7 +616,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._2(p, param.v, param.d)) {
@@ -629,30 +631,30 @@ function exists(p, _param) {
 }
 
 function add_min_binding(k, x, param) {
-  if (param) {
-    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
   }
 }
 
 function add_max_binding(k, x, param) {
-  if (param) {
-    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
   }
 }
 
 function join(l, v, d, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_binding(v, d, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_binding(v, d, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, l.d, join(l.r, v, d, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -663,10 +665,10 @@ function join(l, v, d, r) {
 }
 
 function concat(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -682,7 +684,7 @@ function concat_or_join(t1, v, d, t2) {
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             undefined,
@@ -718,43 +720,46 @@ function split(x, param) {
 }
 
 function merge$1(f, s1, s2) {
-  if (s1) {
+  if (/* tag */typeof s1 === "number") {
+    if (/* tag */typeof s2 === "number") {
+      return /* Empty */0;
+    }
+    
+  } else {
     var v1 = s1.v;
     if (s1.h >= height(s2)) {
       var match = split(v1, s2);
       return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
     }
     
-  } else if (!s2) {
-    return /* Empty */0;
   }
-  if (s2) {
-    var v2 = s2.v;
-    var match$1 = split(v2, s1);
-    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+  if (/* tag */typeof s2 === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "map.ml",
+            393,
+            10
+          ],
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "map.ml",
-          393,
-          10
-        ],
-        Error: new Error()
-      };
+  var v2 = s2.v;
+  var match$1 = split(v2, s1);
+  return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
 }
 
 function union(f, s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var d1 = s1.d;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var d2 = s2.d;
   var v2 = s2.v;
-  var d1 = s1.d;
-  var v1 = s1.v;
   if (s1.h >= s2.h) {
     var match = split(v1, s2);
     var d2$1 = match[1];
@@ -778,7 +783,7 @@ function union(f, s1, s2) {
 }
 
 function filter(p, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -800,7 +805,7 @@ function filter(p, m) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -832,7 +837,7 @@ function cons_enum(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -852,14 +857,14 @@ function compare(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.int_compare(e1._0, e2._0);
@@ -882,14 +887,14 @@ function equal(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (e1._0 !== e2._0) {
@@ -905,10 +910,10 @@ function equal(cmp, m1, m2) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -916,7 +921,7 @@ function bindings_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
diff --git a/jscomp/test/test_int_map_find.js b/jscomp/test/test_int_map_find.js
index 1d2001c83a..a708484c3f 100644
--- a/jscomp/test/test_int_map_find.js
+++ b/jscomp/test/test_int_map_find.js
@@ -4,10 +4,10 @@ var Caml = require("../../lib/js/caml.js");
 var List = require("../../lib/js/list.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -24,26 +24,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -59,23 +61,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -84,7 +86,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
diff --git a/jscomp/test/test_set.js b/jscomp/test/test_set.js
index 9848a27c89..d28613f8a6 100644
--- a/jscomp/test/test_set.js
+++ b/jscomp/test/test_set.js
@@ -5,15 +5,17 @@ var Curry = require("../../lib/js/curry.js");
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param._3;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param._3;
     }
   };
   var create = function (l, v, r) {
-    var hl = l ? l._3 : 0;
-    var hr = r ? r._3 : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l._3;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r._3;
     return /* Node */{
             _0: l,
             _1: v,
@@ -22,25 +24,27 @@ function Make(Ord) {
           };
   };
   var bal = function (l, v, r) {
-    var hl = l ? l._3 : 0;
-    var hr = r ? r._3 : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l._3;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r._3;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l._2;
-        var lv = l._1;
-        var ll = l._0;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, create(lr, v, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
               Error: new Error()
             };
       }
+      var lr = l._2;
+      var lv = l._1;
+      var ll = l._0;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, create(lr, v, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, lr._0), lr._1, create(lr._2, v, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
@@ -55,22 +59,22 @@ function Make(Ord) {
               _3: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r._2;
-      var rv = r._1;
-      var rl = r._0;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, v, rl), rv, rr);
-      }
-      if (rl) {
-        return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var rr = r._2;
+    var rv = r._1;
+    var rl = r._0;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, v, rl), rv, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, v, rl._0), rl._1, create(rl._2, rv, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -78,7 +82,7 @@ function Make(Ord) {
         };
   };
   var add = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Node */{
               _0: /* Empty */0,
               _1: x,
@@ -107,28 +111,28 @@ function Make(Ord) {
           };
   };
   var add_min_element = function (v, param) {
-    if (param) {
-      return bal(add_min_element(v, param._0), param._1, param._2);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(v);
+    } else {
+      return bal(add_min_element(v, param._0), param._1, param._2);
     }
   };
   var add_max_element = function (v, param) {
-    if (param) {
-      return bal(param._0, param._1, add_max_element(v, param._2));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(v);
+    } else {
+      return bal(param._0, param._1, add_max_element(v, param._2));
     }
   };
   var join = function (l, v, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_element(v, r);
     }
-    if (!r) {
+    var lh = l._3;
+    if (/* tag */typeof r === "number") {
       return add_max_element(v, l);
     }
     var rh = r._3;
-    var lh = l._3;
     if (lh > (rh + 2 | 0)) {
       return bal(l._0, l._1, join(l._2, v, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -140,76 +144,72 @@ function Make(Ord) {
   var min_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param._0;
-        if (!l) {
-          return param._1;
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param._0;
+      if (/* tag */typeof l === "number") {
+        return param._1;
+      }
+      _param = l;
+      continue ;
     };
   };
   var max_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param._2;
-        if (!r) {
-          return param._1;
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param._2;
+      if (/* tag */typeof r === "number") {
+        return param._1;
+      }
+      _param = r;
+      continue ;
     };
   };
   var remove_min_elt = function (param) {
-    if (param) {
-      var l = param._0;
-      if (l) {
-        return bal(remove_min_elt(l), param._1, param._2);
-      } else {
-        return param._2;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Set.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param._0;
+    if (/* tag */typeof l === "number") {
+      return param._2;
+    } else {
+      return bal(remove_min_elt(l), param._1, param._2);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return bal(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return bal(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var concat = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return join(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return join(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               false,
@@ -243,16 +243,16 @@ function Make(Ord) {
           ];
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param._1);
@@ -264,7 +264,7 @@ function Make(Ord) {
     };
   };
   var remove = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var r = param._2;
@@ -280,16 +280,16 @@ function Make(Ord) {
     }
   };
   var union = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var h1 = s1._3;
+    var v1 = s1._1;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var h2 = s2._3;
     var v2 = s2._1;
-    var h1 = s1._3;
-    var v1 = s1._1;
     if (h1 >= h2) {
       if (h2 === 1) {
         return add(v2, s1);
@@ -304,10 +304,10 @@ function Make(Ord) {
     return join(union(match$1[0], s2._0), v2, union(match$1[2], s2._2));
   };
   var inter = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return /* Empty */0;
     }
     var r1 = s1._2;
@@ -322,10 +322,10 @@ function Make(Ord) {
     }
   };
   var diff = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var r1 = s1._2;
@@ -343,7 +343,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return e;
       }
       _e = /* More */{
@@ -359,14 +359,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -388,17 +388,17 @@ function Make(Ord) {
     while(true) {
       var s2 = _s2;
       var s1 = _s1;
-      if (!s1) {
+      if (/* tag */typeof s1 === "number") {
         return true;
       }
-      if (!s2) {
+      var r1 = s1._2;
+      var v1 = s1._1;
+      var l1 = s1._0;
+      if (/* tag */typeof s2 === "number") {
         return false;
       }
       var r2 = s2._2;
       var l2 = s2._0;
-      var r1 = s1._2;
-      var v1 = s1._1;
-      var l1 = s1._0;
       var c = Curry._2(Ord.compare, v1, s2._1);
       if (c === 0) {
         if (!subset(l1, l2)) {
@@ -435,7 +435,7 @@ function Make(Ord) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param._0);
@@ -448,7 +448,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return accu;
       }
       _accu = Curry._2(f, s._1, fold(f, s._0, accu));
@@ -459,7 +459,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._1(p, param._1)) {
@@ -475,7 +475,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._1(p, param._1)) {
@@ -489,7 +489,7 @@ function Make(Ord) {
     };
   };
   var filter = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param._1;
@@ -503,7 +503,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -530,17 +530,17 @@ function Make(Ord) {
     }
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param._0) + 1 | 0) + cardinal(param._2) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param._0) + 1 | 0) + cardinal(param._2) | 0;
     }
   };
   var elements_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param._0;
@@ -557,19 +557,19 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param._1;
-        var c = Curry._2(Ord.compare, x, v);
-        if (c === 0) {
-          return v;
-        }
-        _param = c < 0 ? param._0 : param._2;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param._1;
+      var c = Curry._2(Ord.compare, x, v);
+      if (c === 0) {
+        return v;
+      }
+      _param = c < 0 ? param._0 : param._2;
+      continue ;
     };
   };
   var of_sorted_list = function (l) {
diff --git a/jscomp/test/test_string_map.js b/jscomp/test/test_string_map.js
index 876da80f5c..6ace2bd92e 100644
--- a/jscomp/test/test_string_map.js
+++ b/jscomp/test/test_string_map.js
@@ -4,10 +4,10 @@ var Caml = require("../../lib/js/caml.js");
 var Curry = require("../../lib/js/curry.js");
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -24,26 +24,28 @@ function create(l, x, d, r) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -59,23 +61,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -84,7 +86,7 @@ function bal(l, x, d, r) {
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -130,18 +132,18 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml.string_compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml.string_compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
diff --git a/jscomp/test/test_switch.js b/jscomp/test/test_switch.js
index 25a28db097..c33cf9bee2 100644
--- a/jscomp/test/test_switch.js
+++ b/jscomp/test/test_switch.js
@@ -3,7 +3,7 @@
 var Curry = require("../../lib/js/curry.js");
 
 function f(param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     if (param === /* G */0) {
       return 4;
     } else {
diff --git a/jscomp/test/test_trywith.js b/jscomp/test/test_trywith.js
index b9b90b53c0..8829f3b6d6 100644
--- a/jscomp/test/test_trywith.js
+++ b/jscomp/test/test_trywith.js
@@ -123,7 +123,7 @@ function u(param) {
 }
 
 function f(x) {
-  if (typeof x === "number") {
+  if (/* tag */typeof x === "number") {
     return 2;
   }
   if (x.TAG === /* D */0) {
diff --git a/jscomp/test/ticker.js b/jscomp/test/ticker.js
index af6e38bc3d..d03aa30822 100644
--- a/jscomp/test/ticker.js
+++ b/jscomp/test/ticker.js
@@ -67,11 +67,11 @@ var Util = {
 };
 
 function string_of_rank(i) {
-  if (typeof i === "number") {
-    if (i !== 0) {
-      return "Visited";
-    } else {
+  if (/* tag */typeof i === "number") {
+    if (i === /* Uninitialized */0) {
       return "Uninitialized";
+    } else {
+      return "Visited";
     }
   } else {
     return "Ranked(" + i._0 + ")";
@@ -86,19 +86,19 @@ function find_ticker_by_name(all_tickers, ticker) {
 
 function print_all_composite(all_tickers) {
   List.iter((function (param) {
-          if (param.type_) {
-            console.log(param.ticker_name);
+          var tmp = param.type_;
+          if (/* tag */typeof tmp === "number") {
             return ;
           }
-          
+          console.log(param.ticker_name);
         }), all_tickers);
 }
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
@@ -125,26 +125,28 @@ function singleton(x, d) {
 }
 
 function bal(l, x, d, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var ld = l.d;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, ld, create(lr, x, d, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var ld = l.d;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, ld, create(lr, x, d, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -160,23 +162,23 @@ function bal(l, x, d, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rd = r.d;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, x, d, rl), rv, rd, rr);
-    }
-    if (rl) {
-      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rd = r.d;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, x, d, rl), rv, rd, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Map.bal",
@@ -185,15 +187,15 @@ function bal(l, x, d, r) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function add(x, data, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -239,65 +241,65 @@ function add(x, data, m) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var c = Caml_obj.compare(x, param.v);
-      if (c === 0) {
-        return param.d;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var c = Caml_obj.compare(x, param.v);
+    if (c === 0) {
+      return param.d;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -309,7 +311,7 @@ function find_first_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -334,47 +336,47 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _d0 = param.d;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var d0 = _d0;
-          var v0 = _v0;
-          if (!param$1) {
-            return [
-                    v0,
-                    d0
-                  ];
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _d0 = param$1.d;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _d0 = param.d;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var d0 = _d0;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return [
+                  v0,
+                  d0
+                ];
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _d0 = param$1.d;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -386,7 +388,7 @@ function find_last_opt(f, _param) {
         var param$1 = _param$1;
         var d0 = _d0;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return [
                   v0,
                   d0
@@ -411,7 +413,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var c = Caml_obj.compare(x, param.v);
@@ -426,7 +428,7 @@ function find_opt(x, _param) {
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml_obj.compare(x, param.v);
@@ -441,32 +443,32 @@ function mem(x, _param) {
 function min_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return [
               param.v,
               param.d
@@ -480,32 +482,32 @@ function min_binding_opt(_param) {
 function max_binding(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return [
-                param.v,
-                param.d
-              ];
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return [
+              param.v,
+              param.d
+            ];
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_binding_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return [
               param.v,
               param.d
@@ -517,26 +519,26 @@ function max_binding_opt(_param) {
 }
 
 function remove_min_binding(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_binding(l), param.v, param.d, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Map.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_binding(l), param.v, param.d, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Map.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function merge(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -544,7 +546,7 @@ function merge(t1, t2) {
 }
 
 function remove(x, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -572,63 +574,63 @@ function remove(x, m) {
 }
 
 function update(x, f, m) {
-  if (m) {
-    var r = m.r;
-    var d = m.d;
-    var v = m.v;
-    var l = m.l;
-    var c = Caml_obj.compare(x, v);
-    if (c === 0) {
-      var data = Curry._1(f, Caml_option.some(d));
-      if (data === undefined) {
-        return merge(l, r);
-      }
-      var data$1 = Caml_option.valFromOption(data);
-      if (d === data$1) {
-        return m;
-      } else {
-        return /* Node */{
-                l: l,
-                v: x,
-                d: data$1,
-                r: r,
-                h: m.h
-              };
-      }
+  if (/* tag */typeof m === "number") {
+    var data = Curry._1(f, undefined);
+    if (data !== undefined) {
+      return /* Node */{
+              l: /* Empty */0,
+              v: x,
+              d: Caml_option.valFromOption(data),
+              r: /* Empty */0,
+              h: 1
+            };
+    } else {
+      return /* Empty */0;
     }
-    if (c < 0) {
-      var ll = update(x, f, l);
-      if (l === ll) {
-        return m;
-      } else {
-        return bal(ll, v, d, r);
-      }
+  }
+  var r = m.r;
+  var d = m.d;
+  var v = m.v;
+  var l = m.l;
+  var c = Caml_obj.compare(x, v);
+  if (c === 0) {
+    var data$1 = Curry._1(f, Caml_option.some(d));
+    if (data$1 === undefined) {
+      return merge(l, r);
     }
-    var rr = update(x, f, r);
-    if (r === rr) {
+    var data$2 = Caml_option.valFromOption(data$1);
+    if (d === data$2) {
       return m;
     } else {
-      return bal(l, v, d, rr);
+      return /* Node */{
+              l: l,
+              v: x,
+              d: data$2,
+              r: r,
+              h: m.h
+            };
     }
   }
-  var data$2 = Curry._1(f, undefined);
-  if (data$2 !== undefined) {
-    return /* Node */{
-            l: /* Empty */0,
-            v: x,
-            d: Caml_option.valFromOption(data$2),
-            r: /* Empty */0,
-            h: 1
-          };
+  if (c < 0) {
+    var ll = update(x, f, l);
+    if (l === ll) {
+      return m;
+    } else {
+      return bal(ll, v, d, r);
+    }
+  }
+  var rr = update(x, f, r);
+  if (r === rr) {
+    return m;
   } else {
-    return /* Empty */0;
+    return bal(l, v, d, rr);
   }
 }
 
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -639,7 +641,7 @@ function iter(f, _param) {
 }
 
 function map(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var l$p = map(f, param.l);
@@ -655,7 +657,7 @@ function map(f, param) {
 }
 
 function mapi(f, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var v = param.v;
@@ -675,7 +677,7 @@ function fold(f, _m, _accu) {
   while(true) {
     var accu = _accu;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return accu;
     }
     _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -687,7 +689,7 @@ function fold(f, _m, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._2(p, param.v, param.d)) {
@@ -704,7 +706,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._2(p, param.v, param.d)) {
@@ -719,30 +721,30 @@ function exists(p, _param) {
 }
 
 function add_min_binding(k, x, param) {
-  if (param) {
-    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
   }
 }
 
 function add_max_binding(k, x, param) {
-  if (param) {
-    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(k, x);
+  } else {
+    return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
   }
 }
 
 function join(l, v, d, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_binding(v, d, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_binding(v, d, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, l.d, join(l.r, v, d, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -753,10 +755,10 @@ function join(l, v, d, r) {
 }
 
 function concat(t1, t2) {
-  if (!t1) {
+  if (/* tag */typeof t1 === "number") {
     return t2;
   }
-  if (!t2) {
+  if (/* tag */typeof t2 === "number") {
     return t1;
   }
   var match = min_binding(t2);
@@ -772,7 +774,7 @@ function concat_or_join(t1, v, d, t2) {
 }
 
 function split$1(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             undefined,
@@ -808,43 +810,46 @@ function split$1(x, param) {
 }
 
 function merge$1(f, s1, s2) {
-  if (s1) {
+  if (/* tag */typeof s1 === "number") {
+    if (/* tag */typeof s2 === "number") {
+      return /* Empty */0;
+    }
+    
+  } else {
     var v1 = s1.v;
     if (s1.h >= height(s2)) {
       var match = split$1(v1, s2);
       return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
     }
     
-  } else if (!s2) {
-    return /* Empty */0;
   }
-  if (s2) {
-    var v2 = s2.v;
-    var match$1 = split$1(v2, s1);
-    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+  if (/* tag */typeof s2 === "number") {
+    throw {
+          RE_EXN_ID: "Assert_failure",
+          _1: [
+            "map.ml",
+            393,
+            10
+          ],
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: "Assert_failure",
-        _1: [
-          "map.ml",
-          393,
-          10
-        ],
-        Error: new Error()
-      };
+  var v2 = s2.v;
+  var match$1 = split$1(v2, s1);
+  return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
 }
 
 function union(f, s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var d1 = s1.d;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var d2 = s2.d;
   var v2 = s2.v;
-  var d1 = s1.d;
-  var v1 = s1.v;
   if (s1.h >= s2.h) {
     var match = split$1(v1, s2);
     var d2$1 = match[1];
@@ -868,7 +873,7 @@ function union(f, s1, s2) {
 }
 
 function filter(p, m) {
-  if (!m) {
+  if (/* tag */typeof m === "number") {
     return /* Empty */0;
   }
   var r = m.r;
@@ -890,7 +895,7 @@ function filter(p, m) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -922,7 +927,7 @@ function cons_enum(_m, _e) {
   while(true) {
     var e = _e;
     var m = _m;
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return e;
     }
     _e = /* More */{
@@ -942,14 +947,14 @@ function compare(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml_obj.compare(e1._0, e2._0);
@@ -972,14 +977,14 @@ function equal(cmp, m1, m2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return false;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return true;
+      } else {
+        return false;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return false;
     }
     if (!Caml_obj.equal(e1._0, e2._0)) {
@@ -995,10 +1000,10 @@ function equal(cmp, m1, m2) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -1006,7 +1011,7 @@ function bindings_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
@@ -1066,22 +1071,25 @@ function compute_update_sequences(all_tickers) {
   List.fold_left((function (counter, ticker) {
           var loop = function (counter, ticker) {
             var rank = ticker.rank;
-            if (rank !== 0) {
+            if (/* tag */typeof rank !== "number") {
+              return counter;
+            }
+            if (rank !== /* Uninitialized */0) {
               return counter;
             }
             ticker.rank = /* Visited */1;
             var match = ticker.type_;
-            if (match) {
-              var match$1 = match._0;
-              var counter$1 = loop(counter, match$1.lhs);
-              var counter$2 = loop(counter$1, match$1.rhs);
-              var counter$3 = counter$2 + 1 | 0;
+            if (/* tag */typeof match === "number") {
+              var counter$1 = counter + 1 | 0;
               ticker.rank = /* Ranked */{
-                _0: counter$3
+                _0: counter$1
               };
-              return counter$3;
+              return counter$1;
             }
-            var counter$4 = counter + 1 | 0;
+            var match$1 = match._0;
+            var counter$2 = loop(counter, match$1.lhs);
+            var counter$3 = loop(counter$2, match$1.rhs);
+            var counter$4 = counter$3 + 1 | 0;
             ticker.rank = /* Ranked */{
               _0: counter$4
             };
@@ -1090,7 +1098,8 @@ function compute_update_sequences(all_tickers) {
           return loop(counter, ticker);
         }), 0, all_tickers);
   var map = List.fold_left((function (map, ticker) {
-          if (!ticker.type_) {
+          var tmp = ticker.type_;
+          if (/* tag */typeof tmp === "number") {
             return add(ticker.ticker_name, {
                         hd: ticker,
                         tl: /* [] */0
@@ -1103,22 +1112,22 @@ function compute_update_sequences(all_tickers) {
               var up = _up;
               var type_ = ticker.type_;
               var ticker_name = ticker.ticker_name;
-              if (type_) {
-                var match = type_._0;
-                var map$1 = loop({
-                      hd: ticker,
-                      tl: up
-                    }, map, match.lhs);
-                _ticker = match.rhs;
-                _map = map$1;
-                _up = {
-                  hd: ticker,
-                  tl: up
-                };
-                continue ;
+              if (/* tag */typeof type_ === "number") {
+                var l = find(ticker_name, map);
+                return add(ticker_name, Pervasives.$at(up, l), map);
               }
-              var l = find(ticker_name, map);
-              return add(ticker_name, Pervasives.$at(up, l), map);
+              var match = type_._0;
+              var map$1 = loop({
+                    hd: ticker,
+                    tl: up
+                  }, map, match.lhs);
+              _ticker = match.rhs;
+              _map = map$1;
+              _up = {
+                hd: ticker,
+                tl: up
+              };
+              continue ;
             };
           };
           return loop(/* [] */0, map, ticker);
@@ -1126,22 +1135,37 @@ function compute_update_sequences(all_tickers) {
   return fold((function (k, l, map) {
                 var l$1 = List.sort_uniq((function (lhs, rhs) {
                         var x = lhs.rank;
-                        if (typeof x === "number") {
+                        if (/* tag */typeof x === "number") {
+                          if (x === /* Uninitialized */0) {
+                            throw {
+                                  RE_EXN_ID: "Failure",
+                                  _1: "All nodes should be ranked",
+                                  Error: new Error()
+                                };
+                          }
                           throw {
                                 RE_EXN_ID: "Failure",
                                 _1: "All nodes should be ranked",
                                 Error: new Error()
                               };
-                        }
-                        var y = rhs.rank;
-                        if (typeof y === "number") {
+                        } else {
+                          var y = rhs.rank;
+                          if (/* tag */typeof y !== "number") {
+                            return Caml.int_compare(x._0, y._0);
+                          }
+                          if (y === /* Uninitialized */0) {
+                            throw {
+                                  RE_EXN_ID: "Failure",
+                                  _1: "All nodes should be ranked",
+                                  Error: new Error()
+                                };
+                          }
                           throw {
                                 RE_EXN_ID: "Failure",
                                 _1: "All nodes should be ranked",
                                 Error: new Error()
                               };
                         }
-                        return Caml.int_compare(x._0, y._0);
                       }), l);
                 return add(k, l$1, map);
               }), map, map);
@@ -1151,25 +1175,24 @@ function process_quote(ticker_map, new_ticker, new_value) {
   var update_sequence = find(new_ticker, ticker_map);
   List.iter((function (ticker) {
           var match = ticker.type_;
-          if (match) {
-            var match$1 = match._0;
-            var match$2 = match$1.lhs.value;
-            var match$3 = match$1.rhs.value;
-            var value = match$2 !== undefined && match$3 !== undefined ? (
-                match$1.op ? match$2 - match$3 : match$2 + match$3
-              ) : undefined;
-            ticker.value = value;
-            return ;
-          }
-          if (ticker.ticker_name === new_ticker) {
-            ticker.value = new_value;
-            return ;
+          if (/* tag */typeof match === "number") {
+            if (ticker.ticker_name === new_ticker) {
+              ticker.value = new_value;
+              return ;
+            }
+            throw {
+                  RE_EXN_ID: "Failure",
+                  _1: "Only single Market ticker should be udpated upon a new quote",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Failure",
-                _1: "Only single Market ticker should be udpated upon a new quote",
-                Error: new Error()
-              };
+          var match$1 = match._0;
+          var match$2 = match$1.lhs.value;
+          var match$3 = match$1.rhs.value;
+          var value = match$2 !== undefined && match$3 !== undefined ? (
+              match$1.op ? match$2 - match$3 : match$2 + match$3
+            ) : undefined;
+          ticker.value = value;
         }), update_sequence);
 }
 
diff --git a/jscomp/test/topsort_test.js b/jscomp/test/topsort_test.js
index d50dab8c0f..20c1f6340a 100644
--- a/jscomp/test/topsort_test.js
+++ b/jscomp/test/topsort_test.js
@@ -451,16 +451,18 @@ if (!Caml_obj.equal(unsafe_topsort(grwork), {
 }
 
 function height(param) {
-  if (param) {
-    return param.h;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return param.h;
   }
 }
 
 function create(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   return /* Node */{
           l: l,
           v: v,
@@ -470,25 +472,27 @@ function create(l, v, r) {
 }
 
 function bal(l, v, r) {
-  var hl = l ? l.h : 0;
-  var hr = r ? r.h : 0;
+  var hl;
+  hl = /* tag */typeof l === "number" ? 0 : l.h;
+  var hr;
+  hr = /* tag */typeof r === "number" ? 0 : r.h;
   if (hl > (hr + 2 | 0)) {
-    if (l) {
-      var lr = l.r;
-      var lv = l.v;
-      var ll = l.l;
-      if (height(ll) >= height(lr)) {
-        return create(ll, lv, create(lr, v, r));
-      }
-      if (lr) {
-        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-      }
+    if (/* tag */typeof l === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var lr = l.r;
+    var lv = l.v;
+    var ll = l.l;
+    if (height(ll) >= height(lr)) {
+      return create(ll, lv, create(lr, v, r));
+    }
+    if (/* tag */typeof lr !== "number") {
+      return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -503,22 +507,22 @@ function bal(l, v, r) {
             h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
           };
   }
-  if (r) {
-    var rr = r.r;
-    var rv = r.v;
-    var rl = r.l;
-    if (height(rr) >= height(rl)) {
-      return create(create(l, v, rl), rv, rr);
-    }
-    if (rl) {
-      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-    }
+  if (/* tag */typeof r === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
           Error: new Error()
         };
   }
+  var rr = r.r;
+  var rv = r.v;
+  var rl = r.l;
+  if (height(rr) >= height(rl)) {
+    return create(create(l, v, rl), rv, rr);
+  }
+  if (/* tag */typeof rl !== "number") {
+    return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+  }
   throw {
         RE_EXN_ID: "Invalid_argument",
         _1: "Set.bal",
@@ -527,7 +531,7 @@ function bal(l, v, r) {
 }
 
 function add(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Node */{
             l: /* Empty */0,
             v: x,
@@ -568,30 +572,30 @@ function singleton(x) {
 }
 
 function add_min_element(x, param) {
-  if (param) {
-    return bal(add_min_element(x, param.l), param.v, param.r);
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(add_min_element(x, param.l), param.v, param.r);
   }
 }
 
 function add_max_element(x, param) {
-  if (param) {
-    return bal(param.l, param.v, add_max_element(x, param.r));
-  } else {
+  if (/* tag */typeof param === "number") {
     return singleton(x);
+  } else {
+    return bal(param.l, param.v, add_max_element(x, param.r));
   }
 }
 
 function join(l, v, r) {
-  if (!l) {
+  if (/* tag */typeof l === "number") {
     return add_min_element(v, r);
   }
-  if (!r) {
+  var lh = l.h;
+  if (/* tag */typeof r === "number") {
     return add_max_element(v, l);
   }
   var rh = r.h;
-  var lh = l.h;
   if (lh > (rh + 2 | 0)) {
     return bal(l.l, l.v, join(l.r, v, r));
   } else if (rh > (lh + 2 | 0)) {
@@ -604,29 +608,29 @@ function join(l, v, r) {
 function min_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var l = param.l;
-      if (!l) {
-        return param.v;
-      }
-      _param = l;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.v;
+    }
+    _param = l;
+    continue ;
   };
 }
 
 function min_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var l = param.l;
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return Caml_option.some(param.v);
     }
     _param = l;
@@ -637,29 +641,29 @@ function min_elt_opt(_param) {
 function max_elt(_param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var r = param.r;
-      if (!r) {
-        return param.v;
-      }
-      _param = r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var r = param.r;
+    if (/* tag */typeof r === "number") {
+      return param.v;
+    }
+    _param = r;
+    continue ;
   };
 }
 
 function max_elt_opt(_param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var r = param.r;
-    if (!r) {
+    if (/* tag */typeof r === "number") {
       return Caml_option.some(param.v);
     }
     _param = r;
@@ -668,35 +672,33 @@ function max_elt_opt(_param) {
 }
 
 function remove_min_elt(param) {
-  if (param) {
-    var l = param.l;
-    if (l) {
-      return bal(remove_min_elt(l), param.v, param.r);
-    } else {
-      return param.r;
-    }
+  if (/* tag */typeof param === "number") {
+    throw {
+          RE_EXN_ID: "Invalid_argument",
+          _1: "Set.remove_min_elt",
+          Error: new Error()
+        };
+  }
+  var l = param.l;
+  if (/* tag */typeof l === "number") {
+    return param.r;
+  } else {
+    return bal(remove_min_elt(l), param.v, param.r);
   }
-  throw {
-        RE_EXN_ID: "Invalid_argument",
-        _1: "Set.remove_min_elt",
-        Error: new Error()
-      };
 }
 
 function concat(t1, t2) {
-  if (t1) {
-    if (t2) {
-      return join(t1, min_elt(t2), remove_min_elt(t2));
-    } else {
-      return t1;
-    }
-  } else {
+  if (/* tag */typeof t1 === "number") {
     return t2;
+  } else if (/* tag */typeof t2 === "number") {
+    return t1;
+  } else {
+    return join(t1, min_elt(t2), remove_min_elt(t2));
   }
 }
 
 function split(x, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             false,
@@ -731,17 +733,17 @@ function split(x, param) {
 }
 
 function is_empty(param) {
-  if (param) {
-    return false;
-  } else {
+  if (/* tag */typeof param === "number") {
     return true;
+  } else {
+    return false;
   }
 }
 
 function mem(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var c = Caml.string_compare(x, param.v);
@@ -754,7 +756,7 @@ function mem(x, _param) {
 }
 
 function remove(x, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -762,14 +764,12 @@ function remove(x, t) {
   var l = t.l;
   var c = Caml.string_compare(x, v);
   if (c === 0) {
-    if (l) {
-      if (r) {
-        return bal(l, min_elt(r), remove_min_elt(r));
-      } else {
-        return l;
-      }
-    } else {
+    if (/* tag */typeof l === "number") {
       return r;
+    } else if (/* tag */typeof r === "number") {
+      return l;
+    } else {
+      return bal(l, min_elt(r), remove_min_elt(r));
     }
   }
   if (c < 0) {
@@ -789,16 +789,16 @@ function remove(x, t) {
 }
 
 function union(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return s2;
   }
-  if (!s2) {
+  var h1 = s1.h;
+  var v1 = s1.v;
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var h2 = s2.h;
   var v2 = s2.v;
-  var h1 = s1.h;
-  var v1 = s1.v;
   if (h1 >= h2) {
     if (h2 === 1) {
       return add(v2, s1);
@@ -814,10 +814,10 @@ function union(s1, s2) {
 }
 
 function inter(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return /* Empty */0;
   }
   var r1 = s1.r;
@@ -833,10 +833,10 @@ function inter(s1, s2) {
 }
 
 function diff(s1, s2) {
-  if (!s1) {
+  if (/* tag */typeof s1 === "number") {
     return /* Empty */0;
   }
-  if (!s2) {
+  if (/* tag */typeof s2 === "number") {
     return s1;
   }
   var r1 = s1.r;
@@ -855,7 +855,7 @@ function cons_enum(_s, _e) {
   while(true) {
     var e = _e;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return e;
     }
     _e = /* More */{
@@ -874,14 +874,14 @@ function compare(s1, s2) {
   while(true) {
     var e2 = _e2;
     var e1 = _e1;
-    if (!e1) {
-      if (e2) {
-        return -1;
-      } else {
+    if (/* tag */typeof e1 === "number") {
+      if (/* tag */typeof e2 === "number") {
         return 0;
+      } else {
+        return -1;
       }
     }
-    if (!e2) {
+    if (/* tag */typeof e2 === "number") {
       return 1;
     }
     var c = Caml.string_compare(e1._0, e2._0);
@@ -902,17 +902,17 @@ function subset(_s1, _s2) {
   while(true) {
     var s2 = _s2;
     var s1 = _s1;
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return true;
     }
-    if (!s2) {
+    var r1 = s1.r;
+    var v1 = s1.v;
+    var l1 = s1.l;
+    if (/* tag */typeof s2 === "number") {
       return false;
     }
     var r2 = s2.r;
     var l2 = s2.l;
-    var r1 = s1.r;
-    var v1 = s1.v;
-    var l1 = s1.l;
     var c = Caml.string_compare(v1, s2.v);
     if (c === 0) {
       if (!subset(l1, l2)) {
@@ -950,7 +950,7 @@ function subset(_s1, _s2) {
 function iter(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     iter(f, param.l);
@@ -964,7 +964,7 @@ function fold(f, _s, _accu) {
   while(true) {
     var accu = _accu;
     var s = _s;
-    if (!s) {
+    if (/* tag */typeof s === "number") {
       return accu;
     }
     _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -976,7 +976,7 @@ function fold(f, _s, _accu) {
 function for_all(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return true;
     }
     if (!Curry._1(p, param.v)) {
@@ -993,7 +993,7 @@ function for_all(p, _param) {
 function exists(p, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     if (Curry._1(p, param.v)) {
@@ -1008,7 +1008,7 @@ function exists(p, _param) {
 }
 
 function filter(p, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
@@ -1029,7 +1029,7 @@ function filter(p, t) {
 }
 
 function partition(p, param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return [
             /* Empty */0,
             /* Empty */0
@@ -1057,10 +1057,10 @@ function partition(p, param) {
 }
 
 function cardinal(param) {
-  if (param) {
-    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-  } else {
+  if (/* tag */typeof param === "number") {
     return 0;
+  } else {
+    return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
   }
 }
 
@@ -1068,7 +1068,7 @@ function elements_aux(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     _param = param.l;
@@ -1087,60 +1087,60 @@ function elements(s) {
 function find(x, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      var c = Caml.string_compare(x, v);
-      if (c === 0) {
-        return v;
-      }
-      _param = c < 0 ? param.l : param.r;
-      continue ;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var v = param.v;
+    var c = Caml.string_compare(x, v);
+    if (c === 0) {
+      return v;
+    }
+    _param = c < 0 ? param.l : param.r;
+    continue ;
   };
 }
 
 function find_first(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.l;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.l;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.r;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.l;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.l;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.r;
-      continue ;
+        }
+        _param$1 = param$1.r;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.r;
+    continue ;
   };
 }
 
 function find_first_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -1150,7 +1150,7 @@ function find_first_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -1171,41 +1171,41 @@ function find_first_opt(f, _param) {
 function find_last(f, _param) {
   while(true) {
     var param = _param;
-    if (param) {
-      var v = param.v;
-      if (Curry._1(f, v)) {
-        var _v0 = v;
-        var _param$1 = param.r;
-        while(true) {
-          var param$1 = _param$1;
-          var v0 = _v0;
-          if (!param$1) {
-            return v0;
-          }
-          var v$1 = param$1.v;
-          if (Curry._1(f, v$1)) {
-            _param$1 = param$1.r;
-            _v0 = v$1;
-            continue ;
-          }
-          _param$1 = param$1.l;
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var v = param.v;
+    if (Curry._1(f, v)) {
+      var _v0 = v;
+      var _param$1 = param.r;
+      while(true) {
+        var param$1 = _param$1;
+        var v0 = _v0;
+        if (/* tag */typeof param$1 === "number") {
+          return v0;
+        }
+        var v$1 = param$1.v;
+        if (Curry._1(f, v$1)) {
+          _param$1 = param$1.r;
+          _v0 = v$1;
           continue ;
-        };
-      }
-      _param = param.l;
-      continue ;
+        }
+        _param$1 = param$1.l;
+        continue ;
+      };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    _param = param.l;
+    continue ;
   };
 }
 
 function find_last_opt(f, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -1215,7 +1215,7 @@ function find_last_opt(f, _param) {
       while(true) {
         var param$1 = _param$1;
         var v0 = _v0;
-        if (!param$1) {
+        if (/* tag */typeof param$1 === "number") {
           return Caml_option.some(v0);
         }
         var v$1 = param$1.v;
@@ -1236,7 +1236,7 @@ function find_last_opt(f, _param) {
 function find_opt(x, _param) {
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return ;
     }
     var v = param.v;
@@ -1250,7 +1250,7 @@ function find_opt(x, _param) {
 }
 
 function map(f, t) {
-  if (!t) {
+  if (/* tag */typeof t === "number") {
     return /* Empty */0;
   }
   var r = t.r;
diff --git a/jscomp/test/typeof_test.js b/jscomp/test/typeof_test.js
index 50b81ceb30..2d4b5c38f2 100644
--- a/jscomp/test/typeof_test.js
+++ b/jscomp/test/typeof_test.js
@@ -5,7 +5,7 @@ var Js_types = require("../../lib/js/js_types.js");
 
 function string_or_number(x) {
   var ty = Js_types.classify(x);
-  if (typeof ty === "number") {
+  if (/* tag */typeof ty === "number") {
     switch (ty) {
       case /* JSFalse */0 :
       case /* JSTrue */1 :
diff --git a/jscomp/test/utf8_decode_test.js b/jscomp/test/utf8_decode_test.js
index 47ea4126e3..7ffe3a6440 100644
--- a/jscomp/test/utf8_decode_test.js
+++ b/jscomp/test/utf8_decode_test.js
@@ -60,7 +60,7 @@ function utf8_decode(strm) {
               }
               Stream.junk(strm);
               var c = classify(chr);
-              if (typeof c === "number") {
+              if (/* tag */typeof c === "number") {
                 throw {
                       RE_EXN_ID: Stream.$$Error,
                       _1: "Invalid byte",
@@ -85,7 +85,7 @@ function utf8_decode(strm) {
                           return c;
                         }
                         var cc = classify(Stream.next(strm));
-                        if (typeof cc === "number") {
+                        if (/* tag */typeof cc === "number") {
                           throw {
                                 RE_EXN_ID: Stream.$$Error,
                                 _1: "Continuation byte expected",
@@ -129,7 +129,7 @@ function utf8_list(s) {
 
 function decode(bytes, offset) {
   var c = classify(Caml_bytes.get(bytes, offset));
-  if (typeof c === "number") {
+  if (/* tag */typeof c === "number") {
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "decode",
@@ -163,7 +163,7 @@ function decode(bytes, offset) {
                   ];
           }
           var cc = classify(Caml_bytes.get(bytes, offset$1));
-          if (typeof cc === "number") {
+          if (/* tag */typeof cc === "number") {
             throw {
                   RE_EXN_ID: "Invalid_argument",
                   _1: "decode",
diff --git a/jscomp/test/variant.js b/jscomp/test/variant.js
index 32c17e781c..5de53d25f8 100644
--- a/jscomp/test/variant.js
+++ b/jscomp/test/variant.js
@@ -6,7 +6,7 @@ var Caml_exceptions = require("../../lib/js/caml_exceptions.js");
 var Caml_js_exceptions = require("../../lib/js/caml_js_exceptions.js");
 
 function foo(n) {
-  if (typeof n === "number") {
+  if (/* tag */typeof n === "number") {
     if (n === /* A1 */0) {
       return 1;
     } else {
@@ -26,7 +26,7 @@ function foo(n) {
 }
 
 function fooA1(param) {
-  if (param === 0) {
+  if (/* tag */typeof param === "number" && param === /* A1 */0) {
     return 1;
   } else {
     return 42;
@@ -34,7 +34,7 @@ function fooA1(param) {
 }
 
 function fooC(param) {
-  if (typeof param === "number" || param.TAG !== /* C */1) {
+  if (/* tag */typeof param === "number" || param.TAG !== /* C */1) {
     return 42;
   } else {
     return param._0 + param._1 | 0;
diff --git a/jscomp/test/variantsMatching.js b/jscomp/test/variantsMatching.js
new file mode 100644
index 0000000000..52fb50e686
--- /dev/null
+++ b/jscomp/test/variantsMatching.js
@@ -0,0 +1,147 @@
+'use strict';
+
+
+function toEnum(x) {
+  switch (x) {
+    case /* A */0 :
+        return 0;
+    case /* B */1 :
+        return 1;
+    case /* C */2 :
+        return 2;
+    case /* D */3 :
+        return 3;
+    case /* E */4 :
+        return 4;
+    
+  }
+}
+
+function toString(x) {
+  switch (x) {
+    case /* A */0 :
+        return "A";
+    case /* B */1 :
+        return "B";
+    case /* C */2 :
+        return "C";
+    case /* D */3 :
+        return "D";
+    case /* E */4 :
+        return "E";
+    
+  }
+}
+
+function bar(x) {
+  switch (x) {
+    case /* A */0 :
+    case /* E */4 :
+        return 10;
+    default:
+      return 0;
+  }
+}
+
+function and_(x, y) {
+  if (x === /* True */0 && y === /* True */0) {
+    return /* True */0;
+  } else {
+    return /* False */1;
+  }
+}
+
+function id(x) {
+  if (x === /* True */0) {
+    return /* True */0;
+  } else {
+    return /* False */1;
+  }
+}
+
+function not_(x) {
+  if (x === /* True */0) {
+    return /* False */1;
+  } else {
+    return /* True */0;
+  }
+}
+
+function st(state) {
+  if (/* tag */typeof state === "number") {
+    return 0;
+  } else {
+    return 23;
+  }
+}
+
+function showToJs(x) {
+  if (/* tag */typeof x === "number" && x === /* No */0) {
+    return false;
+  } else {
+    return true;
+  }
+}
+
+function third(l) {
+  if (!l) {
+    return false;
+  }
+  if (l.hd !== 1) {
+    return false;
+  }
+  var match = l.tl;
+  if (!match) {
+    return false;
+  }
+  if (match.hd !== 2) {
+    return false;
+  }
+  var match$1 = match.tl;
+  if (match$1 && !(match$1.hd !== 3 || match$1.tl)) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+function third2(l) {
+  if (/* tag */typeof l === "number") {
+    return false;
+  }
+  if (l._0 !== 1) {
+    return false;
+  }
+  var match = l._1;
+  if (/* tag */typeof match === "number") {
+    return false;
+  }
+  if (match._0 !== 2) {
+    return false;
+  }
+  var match$1 = match._1;
+  if (/* tag */typeof match$1 === "number") {
+    return false;
+  }
+  if (match$1._0 !== 3) {
+    return false;
+  }
+  var tmp = match$1._1;
+  if (/* tag */typeof tmp === "number") {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+exports.toEnum = toEnum;
+exports.toString = toString;
+exports.bar = bar;
+exports.and_ = and_;
+exports.id = id;
+exports.not_ = not_;
+exports.st = st;
+exports.showToJs = showToJs;
+exports.third = third;
+exports.third2 = third2;
+/* No side effect */
diff --git a/jscomp/test/variantsMatching.res b/jscomp/test/variantsMatching.res
new file mode 100644
index 0000000000..a95c89c8ed
--- /dev/null
+++ b/jscomp/test/variantsMatching.res
@@ -0,0 +1,81 @@
+type t = A | B | C | D | E
+
+let toEnum = x =>
+  switch x {
+  | A => 0
+  | B => 1
+  | C => 2
+  | D => 3
+  | E => 4
+  }
+
+let toString = x =>
+  switch x {
+  | A => "A"
+  | B => "B"
+  | C => "C"
+  | D => "D"
+  | E => "E"
+  }
+
+let bar = x =>
+  switch x {
+  | A => 10
+  | B | C | D => 0
+  | E => 10
+  }
+
+type b = True | False
+
+let and_ = (x, y) =>
+  switch (x, y) {
+  | (True, False) => False
+  | (False, True) => False
+  | (False, False) => False
+  | (True, True) => True
+  }
+
+let id = x =>
+  switch x {
+  | True => True
+  | False => False
+  }
+
+let not_ = x =>
+  switch x {
+  | True => False
+  | False => True
+  }
+
+type state =
+  | Empty
+  | Int1(int)
+  | Int2(int)
+let st = state =>
+  switch state {
+  | Empty => 0
+  | Int2(intValue)
+  | Int1(intValue) => 23
+  }
+
+type show = No | After(int) | Yes
+
+let showToJs = x =>
+  switch x {
+  | Yes | After(_) => true
+  | No => false
+  }
+
+let third = l =>
+  switch l {
+  | list{1, 2, 3} => true
+  | _ => false
+  }
+
+type rec lst = Empty | Cons(int, lst)
+
+let third2 = l =>
+  switch l {
+  | Cons(1, Cons(2, Cons(3, Empty))) => true
+  | _ => false
+  }
diff --git a/lib/es6/caml_module.js b/lib/es6/caml_module.js
index da6f76c557..19f6b76153 100644
--- a/lib/es6/caml_module.js
+++ b/lib/es6/caml_module.js
@@ -11,7 +11,7 @@ function init_mod(loc, shape) {
         };
   };
   var loop = function (shape, struct_, idx) {
-    if (typeof shape === "number") {
+    if (/* tag */typeof shape === "number") {
       switch (shape) {
         case /* Function */0 :
             struct_[idx] = undef_module;
@@ -56,7 +56,7 @@ function init_mod(loc, shape) {
 
 function update_mod(shape, o, n) {
   var aux = function (shape, o, n, parent, i) {
-    if (typeof shape === "number") {
+    if (/* tag */typeof shape === "number") {
       switch (shape) {
         case /* Function */0 :
             parent[i] = n;
@@ -79,7 +79,7 @@ function update_mod(shape, o, n) {
       return ;
     }
   };
-  if (typeof shape === "number") {
+  if (/* tag */typeof shape === "number") {
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
diff --git a/lib/es6/hashtbl.js b/lib/es6/hashtbl.js
index 995edd7ea2..bcca2e756c 100644
--- a/lib/es6/hashtbl.js
+++ b/lib/es6/hashtbl.js
@@ -92,7 +92,7 @@ function reset(h) {
 }
 
 function copy_bucketlist(param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var key = param.key;
@@ -102,7 +102,7 @@ function copy_bucketlist(param) {
     while(true) {
       var param = _param;
       var prec = _prec;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var key = param.key;
@@ -113,9 +113,7 @@ function copy_bucketlist(param) {
         data: data,
         next: next
       };
-      if (prec) {
-        prec.next = r;
-      } else {
+      if (/* tag */typeof prec === "number") {
         throw {
               RE_EXN_ID: "Assert_failure",
               _1: [
@@ -126,6 +124,7 @@ function copy_bucketlist(param) {
               Error: new Error()
             };
       }
+      prec.next = r;
       _param = next;
       _prec = r;
       continue ;
@@ -167,7 +166,7 @@ function resize(indexfun, h) {
   var insert_bucket = function (_cell) {
     while(true) {
       var cell = _cell;
-      if (!cell) {
+      if (/* tag */typeof cell === "number") {
         return ;
       }
       var key = cell.key;
@@ -180,10 +179,10 @@ function resize(indexfun, h) {
           });
       var nidx = Curry._2(indexfun, h, key);
       var tail = Caml_array.get(ndata_tail, nidx);
-      if (tail) {
-        tail.next = cell$1;
-      } else {
+      if (/* tag */typeof tail === "number") {
         Caml_array.set(ndata, nidx, cell$1);
+      } else {
+        tail.next = cell$1;
       }
       Caml_array.set(ndata_tail, nidx, cell$1);
       _cell = next;
@@ -198,7 +197,7 @@ function resize(indexfun, h) {
   }
   for(var i$1 = 0; i$1 < nsize; ++i$1){
     var tail = Caml_array.get(ndata_tail, i$1);
-    if (tail) {
+    if (/* tag */typeof tail !== "number") {
       tail.next = /* Empty */0;
     }
     
@@ -231,18 +230,18 @@ function remove(h, key) {
   while(true) {
     var c = _c;
     var prec = _prec;
-    if (!c) {
+    if (/* tag */typeof c === "number") {
       return ;
     }
     var k = c.key;
     var next = c.next;
     if (Caml_obj.equal(k, key)) {
       h.size = h.size - 1 | 0;
-      if (prec) {
+      if (/* tag */typeof prec === "number") {
+        return Caml_array.set(h.data, i, next);
+      } else {
         prec.next = next;
         return ;
-      } else {
-        return Caml_array.set(h.data, i, next);
       }
     }
     _c = next;
@@ -253,66 +252,66 @@ function remove(h, key) {
 
 function find(h, key) {
   var match = Caml_array.get(h.data, key_index(h, key));
-  if (match) {
-    var k1 = match.key;
-    var d1 = match.data;
-    var next1 = match.next;
-    if (Caml_obj.equal(key, k1)) {
-      return d1;
-    }
-    if (next1) {
-      var k2 = next1.key;
-      var d2 = next1.data;
-      var next2 = next1.next;
-      if (Caml_obj.equal(key, k2)) {
-        return d2;
-      }
-      if (next2) {
-        var k3 = next2.key;
-        var d3 = next2.data;
-        var next3 = next2.next;
-        if (Caml_obj.equal(key, k3)) {
-          return d3;
-        } else {
-          var _param = next3;
-          while(true) {
-            var param = _param;
-            if (param) {
-              var k = param.key;
-              var data = param.data;
-              var next = param.next;
-              if (Caml_obj.equal(key, k)) {
-                return data;
-              }
-              _param = next;
-              continue ;
-            }
-            throw {
-                  RE_EXN_ID: "Not_found",
-                  Error: new Error()
-                };
-          };
-        }
-      }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
-    }
+  if (/* tag */typeof match === "number") {
     throw {
           RE_EXN_ID: "Not_found",
           Error: new Error()
         };
   }
-  throw {
-        RE_EXN_ID: "Not_found",
-        Error: new Error()
-      };
+  var k1 = match.key;
+  var d1 = match.data;
+  var next1 = match.next;
+  if (Caml_obj.equal(key, k1)) {
+    return d1;
+  }
+  if (/* tag */typeof next1 === "number") {
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
+  }
+  var k2 = next1.key;
+  var d2 = next1.data;
+  var next2 = next1.next;
+  if (Caml_obj.equal(key, k2)) {
+    return d2;
+  }
+  if (/* tag */typeof next2 === "number") {
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
+  }
+  var k3 = next2.key;
+  var d3 = next2.data;
+  var next3 = next2.next;
+  if (Caml_obj.equal(key, k3)) {
+    return d3;
+  } else {
+    var _param = next3;
+    while(true) {
+      var param = _param;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var k = param.key;
+      var data = param.data;
+      var next = param.next;
+      if (Caml_obj.equal(key, k)) {
+        return data;
+      }
+      _param = next;
+      continue ;
+    };
+  }
 }
 
 function find_opt(h, key) {
   var match = Caml_array.get(h.data, key_index(h, key));
-  if (!match) {
+  if (/* tag */typeof match === "number") {
     return ;
   }
   var k1 = match.key;
@@ -321,7 +320,7 @@ function find_opt(h, key) {
   if (Caml_obj.equal(key, k1)) {
     return Caml_option.some(d1);
   }
-  if (!next1) {
+  if (/* tag */typeof next1 === "number") {
     return ;
   }
   var k2 = next1.key;
@@ -330,7 +329,7 @@ function find_opt(h, key) {
   if (Caml_obj.equal(key, k2)) {
     return Caml_option.some(d2);
   }
-  if (!next2) {
+  if (/* tag */typeof next2 === "number") {
     return ;
   }
   var k3 = next2.key;
@@ -342,7 +341,7 @@ function find_opt(h, key) {
     var _param = next3;
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var k = param.key;
@@ -361,7 +360,7 @@ function find_all(h, key) {
   var find_in_bucket = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return /* [] */0;
       }
       var k = param.key;
@@ -383,7 +382,7 @@ function find_all(h, key) {
 function replace_bucket(key, data, _slot) {
   while(true) {
     var slot = _slot;
-    if (!slot) {
+    if (/* tag */typeof slot === "number") {
       return true;
     }
     var k = slot.key;
@@ -421,7 +420,7 @@ function mem(h, key) {
   var _param = Caml_array.get(h.data, key_index(h, key));
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var k = param.key;
@@ -438,7 +437,7 @@ function iter(f, h) {
   var do_bucket = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var key = param.key;
@@ -477,12 +476,12 @@ function filter_map_inplace_bucket(f, h, i, _prec, _slot) {
   while(true) {
     var slot = _slot;
     var prec = _prec;
-    if (!slot) {
-      if (prec) {
+    if (/* tag */typeof slot === "number") {
+      if (/* tag */typeof prec === "number") {
+        return Caml_array.set(h.data, i, /* Empty */0);
+      } else {
         prec.next = /* Empty */0;
         return ;
-      } else {
-        return Caml_array.set(h.data, i, /* Empty */0);
       }
     }
     var key = slot.key;
@@ -490,10 +489,10 @@ function filter_map_inplace_bucket(f, h, i, _prec, _slot) {
     var next = slot.next;
     var data$1 = Curry._2(f, key, data);
     if (data$1 !== undefined) {
-      if (prec) {
-        prec.next = slot;
-      } else {
+      if (/* tag */typeof prec === "number") {
         Caml_array.set(h.data, i, slot);
+      } else {
+        prec.next = slot;
       }
       slot.data = Caml_option.valFromOption(data$1);
       _slot = next;
@@ -532,7 +531,7 @@ function fold(f, h, init) {
     while(true) {
       var accu = _accu;
       var b = _b;
-      if (!b) {
+      if (/* tag */typeof b === "number") {
         return accu;
       }
       var key = b.key;
@@ -571,7 +570,7 @@ function bucket_length(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     var next = param.next;
@@ -623,18 +622,18 @@ function MakeSeeded(H) {
     while(true) {
       var c = _c;
       var prec = _prec;
-      if (!c) {
+      if (/* tag */typeof c === "number") {
         return ;
       }
       var k = c.key;
       var next = c.next;
       if (Curry._2(H.equal, k, key)) {
         h.size = h.size - 1 | 0;
-        if (prec) {
+        if (/* tag */typeof prec === "number") {
+          return Caml_array.set(h.data, i, next);
+        } else {
           prec.next = next;
           return ;
-        } else {
-          return Caml_array.set(h.data, i, next);
         }
       }
       _c = next;
@@ -644,65 +643,65 @@ function MakeSeeded(H) {
   };
   var find = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (match) {
-      var k1 = match.key;
-      var d1 = match.data;
-      var next1 = match.next;
-      if (Curry._2(H.equal, key, k1)) {
-        return d1;
-      }
-      if (next1) {
-        var k2 = next1.key;
-        var d2 = next1.data;
-        var next2 = next1.next;
-        if (Curry._2(H.equal, key, k2)) {
-          return d2;
-        }
-        if (next2) {
-          var k3 = next2.key;
-          var d3 = next2.data;
-          var next3 = next2.next;
-          if (Curry._2(H.equal, key, k3)) {
-            return d3;
-          } else {
-            var _param = next3;
-            while(true) {
-              var param = _param;
-              if (param) {
-                var k = param.key;
-                var data = param.data;
-                var next = param.next;
-                if (Curry._2(H.equal, key, k)) {
-                  return data;
-                }
-                _param = next;
-                continue ;
-              }
-              throw {
-                    RE_EXN_ID: "Not_found",
-                    Error: new Error()
-                  };
-            };
-          }
-        }
-        throw {
-              RE_EXN_ID: "Not_found",
-              Error: new Error()
-            };
-      }
+    if (/* tag */typeof match === "number") {
       throw {
             RE_EXN_ID: "Not_found",
             Error: new Error()
           };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var k1 = match.key;
+    var d1 = match.data;
+    var next1 = match.next;
+    if (Curry._2(H.equal, key, k1)) {
+      return d1;
+    }
+    if (/* tag */typeof next1 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k2 = next1.key;
+    var d2 = next1.data;
+    var next2 = next1.next;
+    if (Curry._2(H.equal, key, k2)) {
+      return d2;
+    }
+    if (/* tag */typeof next2 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k3 = next2.key;
+    var d3 = next2.data;
+    var next3 = next2.next;
+    if (Curry._2(H.equal, key, k3)) {
+      return d3;
+    } else {
+      var _param = next3;
+      while(true) {
+        var param = _param;
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Not_found",
+                Error: new Error()
+              };
+        }
+        var k = param.key;
+        var data = param.data;
+        var next = param.next;
+        if (Curry._2(H.equal, key, k)) {
+          return data;
+        }
+        _param = next;
+        continue ;
+      };
+    }
   };
   var find_opt = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (!match) {
+    if (/* tag */typeof match === "number") {
       return ;
     }
     var k1 = match.key;
@@ -711,7 +710,7 @@ function MakeSeeded(H) {
     if (Curry._2(H.equal, key, k1)) {
       return Caml_option.some(d1);
     }
-    if (!next1) {
+    if (/* tag */typeof next1 === "number") {
       return ;
     }
     var k2 = next1.key;
@@ -720,7 +719,7 @@ function MakeSeeded(H) {
     if (Curry._2(H.equal, key, k2)) {
       return Caml_option.some(d2);
     }
-    if (!next2) {
+    if (/* tag */typeof next2 === "number") {
       return ;
     }
     var k3 = next2.key;
@@ -732,7 +731,7 @@ function MakeSeeded(H) {
       var _param = next3;
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return ;
         }
         var k = param.key;
@@ -750,7 +749,7 @@ function MakeSeeded(H) {
     var find_in_bucket = function (_param) {
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* [] */0;
         }
         var k = param.key;
@@ -771,7 +770,7 @@ function MakeSeeded(H) {
   var replace_bucket = function (key, data, _slot) {
     while(true) {
       var slot = _slot;
-      if (!slot) {
+      if (/* tag */typeof slot === "number") {
         return true;
       }
       var k = slot.key;
@@ -807,7 +806,7 @@ function MakeSeeded(H) {
     var _param = Caml_array.get(h.data, key_index(h, key));
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var k = param.key;
@@ -865,18 +864,18 @@ function Make(H) {
     while(true) {
       var c = _c;
       var prec = _prec;
-      if (!c) {
+      if (/* tag */typeof c === "number") {
         return ;
       }
       var k = c.key;
       var next = c.next;
       if (Curry._2(equal, k, key)) {
         h.size = h.size - 1 | 0;
-        if (prec) {
+        if (/* tag */typeof prec === "number") {
+          return Caml_array.set(h.data, i, next);
+        } else {
           prec.next = next;
           return ;
-        } else {
-          return Caml_array.set(h.data, i, next);
         }
       }
       _c = next;
@@ -886,65 +885,65 @@ function Make(H) {
   };
   var find = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (match) {
-      var k1 = match.key;
-      var d1 = match.data;
-      var next1 = match.next;
-      if (Curry._2(equal, key, k1)) {
-        return d1;
-      }
-      if (next1) {
-        var k2 = next1.key;
-        var d2 = next1.data;
-        var next2 = next1.next;
-        if (Curry._2(equal, key, k2)) {
-          return d2;
-        }
-        if (next2) {
-          var k3 = next2.key;
-          var d3 = next2.data;
-          var next3 = next2.next;
-          if (Curry._2(equal, key, k3)) {
-            return d3;
-          } else {
-            var _param = next3;
-            while(true) {
-              var param = _param;
-              if (param) {
-                var k = param.key;
-                var data = param.data;
-                var next = param.next;
-                if (Curry._2(equal, key, k)) {
-                  return data;
-                }
-                _param = next;
-                continue ;
-              }
-              throw {
-                    RE_EXN_ID: "Not_found",
-                    Error: new Error()
-                  };
-            };
-          }
-        }
-        throw {
-              RE_EXN_ID: "Not_found",
-              Error: new Error()
-            };
-      }
+    if (/* tag */typeof match === "number") {
       throw {
             RE_EXN_ID: "Not_found",
             Error: new Error()
           };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var k1 = match.key;
+    var d1 = match.data;
+    var next1 = match.next;
+    if (Curry._2(equal, key, k1)) {
+      return d1;
+    }
+    if (/* tag */typeof next1 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k2 = next1.key;
+    var d2 = next1.data;
+    var next2 = next1.next;
+    if (Curry._2(equal, key, k2)) {
+      return d2;
+    }
+    if (/* tag */typeof next2 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k3 = next2.key;
+    var d3 = next2.data;
+    var next3 = next2.next;
+    if (Curry._2(equal, key, k3)) {
+      return d3;
+    } else {
+      var _param = next3;
+      while(true) {
+        var param = _param;
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Not_found",
+                Error: new Error()
+              };
+        }
+        var k = param.key;
+        var data = param.data;
+        var next = param.next;
+        if (Curry._2(equal, key, k)) {
+          return data;
+        }
+        _param = next;
+        continue ;
+      };
+    }
   };
   var find_opt = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (!match) {
+    if (/* tag */typeof match === "number") {
       return ;
     }
     var k1 = match.key;
@@ -953,7 +952,7 @@ function Make(H) {
     if (Curry._2(equal, key, k1)) {
       return Caml_option.some(d1);
     }
-    if (!next1) {
+    if (/* tag */typeof next1 === "number") {
       return ;
     }
     var k2 = next1.key;
@@ -962,7 +961,7 @@ function Make(H) {
     if (Curry._2(equal, key, k2)) {
       return Caml_option.some(d2);
     }
-    if (!next2) {
+    if (/* tag */typeof next2 === "number") {
       return ;
     }
     var k3 = next2.key;
@@ -974,7 +973,7 @@ function Make(H) {
       var _param = next3;
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return ;
         }
         var k = param.key;
@@ -992,7 +991,7 @@ function Make(H) {
     var find_in_bucket = function (_param) {
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* [] */0;
         }
         var k = param.key;
@@ -1013,7 +1012,7 @@ function Make(H) {
   var replace_bucket = function (key, data, _slot) {
     while(true) {
       var slot = _slot;
-      if (!slot) {
+      if (/* tag */typeof slot === "number") {
         return true;
       }
       var k = slot.key;
@@ -1049,7 +1048,7 @@ function Make(H) {
     var _param = Caml_array.get(h.data, key_index(h, key));
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var k = param.key;
diff --git a/lib/es6/map.js b/lib/es6/map.js
index 5a1c45d078..91fbbab1b6 100644
--- a/lib/es6/map.js
+++ b/lib/es6/map.js
@@ -5,10 +5,10 @@ import * as Caml_option from "./caml_option.js";
 
 function Make(funarg) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, x, d, r) {
@@ -32,26 +32,28 @@ function Make(funarg) {
           };
   };
   var bal = function (l, x, d, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var ld = l.d;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, ld, create(lr, x, d, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var ld = l.d;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, ld, create(lr, x, d, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
@@ -67,23 +69,23 @@ function Make(funarg) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rd = r.d;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, x, d, rl), rv, rd, rr);
-      }
-      if (rl) {
-        return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rd = r.d;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, x, d, rl), rv, rd, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -91,14 +93,14 @@ function Make(funarg) {
         };
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var add = function (x, data, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -143,63 +145,63 @@ function Make(funarg) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var c = Curry._2(funarg.compare, x, param.v);
-        if (c === 0) {
-          return param.d;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = Curry._2(funarg.compare, x, param.v);
+      if (c === 0) {
+        return param.d;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _d0 = param.d;
-          var _param$1 = param.l;
-          while(true) {
-            var param$1 = _param$1;
-            var d0 = _d0;
-            var v0 = _v0;
-            if (!param$1) {
-              return [
-                      v0,
-                      d0
-                    ];
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.l;
-              _d0 = param$1.d;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.r;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _d0 = param.d;
+        var _param$1 = param.l;
+        while(true) {
+          var param$1 = _param$1;
+          var d0 = _d0;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return [
+                    v0,
+                    d0
+                  ];
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.l;
+            _d0 = param$1.d;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.r;
-        continue ;
+          }
+          _param$1 = param$1.r;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -211,7 +213,7 @@ function Make(funarg) {
           var param$1 = _param$1;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return [
                     v0,
                     d0
@@ -235,46 +237,46 @@ function Make(funarg) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _d0 = param.d;
-          var _param$1 = param.r;
-          while(true) {
-            var param$1 = _param$1;
-            var d0 = _d0;
-            var v0 = _v0;
-            if (!param$1) {
-              return [
-                      v0,
-                      d0
-                    ];
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.r;
-              _d0 = param$1.d;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.l;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _d0 = param.d;
+        var _param$1 = param.r;
+        while(true) {
+          var param$1 = _param$1;
+          var d0 = _d0;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return [
+                    v0,
+                    d0
+                  ];
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.r;
+            _d0 = param$1.d;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.l;
-        continue ;
+          }
+          _param$1 = param$1.l;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -286,7 +288,7 @@ function Make(funarg) {
           var param$1 = _param$1;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return [
                     v0,
                     d0
@@ -310,7 +312,7 @@ function Make(funarg) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -324,7 +326,7 @@ function Make(funarg) {
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -338,31 +340,31 @@ function Make(funarg) {
   var min_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return [
                 param.v,
                 param.d
@@ -375,31 +377,31 @@ function Make(funarg) {
   var max_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return [
                 param.v,
                 param.d
@@ -410,32 +412,32 @@ function Make(funarg) {
     };
   };
   var remove_min_binding = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_binding(l), param.v, param.d, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Map.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_binding(l), param.v, param.d, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
     return bal(t1, match[0], match[1], remove_min_binding(t2));
   };
   var remove = function (x, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -462,62 +464,62 @@ function Make(funarg) {
     }
   };
   var update = function (x, f, m) {
-    if (m) {
-      var r = m.r;
-      var d = m.d;
-      var v = m.v;
-      var l = m.l;
-      var c = Curry._2(funarg.compare, x, v);
-      if (c === 0) {
-        var data = Curry._1(f, Caml_option.some(d));
-        if (data === undefined) {
-          return merge(l, r);
-        }
-        var data$1 = Caml_option.valFromOption(data);
-        if (d === data$1) {
-          return m;
-        } else {
-          return /* Node */{
-                  l: l,
-                  v: x,
-                  d: data$1,
-                  r: r,
-                  h: m.h
-                };
-        }
+    if (/* tag */typeof m === "number") {
+      var data = Curry._1(f, undefined);
+      if (data !== undefined) {
+        return /* Node */{
+                l: /* Empty */0,
+                v: x,
+                d: Caml_option.valFromOption(data),
+                r: /* Empty */0,
+                h: 1
+              };
+      } else {
+        return /* Empty */0;
       }
-      if (c < 0) {
-        var ll = update(x, f, l);
-        if (l === ll) {
-          return m;
-        } else {
-          return bal(ll, v, d, r);
-        }
+    }
+    var r = m.r;
+    var d = m.d;
+    var v = m.v;
+    var l = m.l;
+    var c = Curry._2(funarg.compare, x, v);
+    if (c === 0) {
+      var data$1 = Curry._1(f, Caml_option.some(d));
+      if (data$1 === undefined) {
+        return merge(l, r);
+      }
+      var data$2 = Caml_option.valFromOption(data$1);
+      if (d === data$2) {
+        return m;
+      } else {
+        return /* Node */{
+                l: l,
+                v: x,
+                d: data$2,
+                r: r,
+                h: m.h
+              };
       }
-      var rr = update(x, f, r);
-      if (r === rr) {
+    }
+    if (c < 0) {
+      var ll = update(x, f, l);
+      if (l === ll) {
         return m;
       } else {
-        return bal(l, v, d, rr);
+        return bal(ll, v, d, r);
       }
     }
-    var data$2 = Curry._1(f, undefined);
-    if (data$2 !== undefined) {
-      return /* Node */{
-              l: /* Empty */0,
-              v: x,
-              d: Caml_option.valFromOption(data$2),
-              r: /* Empty */0,
-              h: 1
-            };
+    var rr = update(x, f, r);
+    if (r === rr) {
+      return m;
     } else {
-      return /* Empty */0;
+      return bal(l, v, d, rr);
     }
   };
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -527,7 +529,7 @@ function Make(funarg) {
     };
   };
   var map = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var l$p = map(f, param.l);
@@ -542,7 +544,7 @@ function Make(funarg) {
           };
   };
   var mapi = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param.v;
@@ -561,7 +563,7 @@ function Make(funarg) {
     while(true) {
       var accu = _accu;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return accu;
       }
       _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -572,7 +574,7 @@ function Make(funarg) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._2(p, param.v, param.d)) {
@@ -588,7 +590,7 @@ function Make(funarg) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._2(p, param.v, param.d)) {
@@ -602,28 +604,28 @@ function Make(funarg) {
     };
   };
   var add_min_binding = function (k, x, param) {
-    if (param) {
-      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
     }
   };
   var add_max_binding = function (k, x, param) {
-    if (param) {
-      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
     }
   };
   var join = function (l, v, d, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_binding(v, d, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_binding(v, d, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, l.d, join(l.r, v, d, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -633,10 +635,10 @@ function Make(funarg) {
     }
   };
   var concat = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
@@ -650,7 +652,7 @@ function Make(funarg) {
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               undefined,
@@ -685,42 +687,45 @@ function Make(funarg) {
           ];
   };
   var merge$1 = function (f, s1, s2) {
-    if (s1) {
+    if (/* tag */typeof s1 === "number") {
+      if (/* tag */typeof s2 === "number") {
+        return /* Empty */0;
+      }
+      
+    } else {
       var v1 = s1.v;
       if (s1.h >= height(s2)) {
         var match = split(v1, s2);
         return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
       }
       
-    } else if (!s2) {
-      return /* Empty */0;
     }
-    if (s2) {
-      var v2 = s2.v;
-      var match$1 = split(v2, s1);
-      return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+    if (/* tag */typeof s2 === "number") {
+      throw {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "map.ml",
+              393,
+              10
+            ],
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "map.ml",
-            393,
-            10
-          ],
-          Error: new Error()
-        };
+    var v2 = s2.v;
+    var match$1 = split(v2, s1);
+    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   };
   var union = function (f, s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var d1 = s1.d;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var d2 = s2.d;
     var v2 = s2.v;
-    var d1 = s1.d;
-    var v1 = s1.v;
     if (s1.h >= s2.h) {
       var match = split(v1, s2);
       var d2$1 = match[1];
@@ -743,7 +748,7 @@ function Make(funarg) {
     }
   };
   var filter = function (p, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -764,7 +769,7 @@ function Make(funarg) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -795,7 +800,7 @@ function Make(funarg) {
     while(true) {
       var e = _e;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return e;
       }
       _e = /* More */{
@@ -814,14 +819,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -843,14 +848,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return false;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return true;
+        } else {
+          return false;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return false;
       }
       if (Curry._2(funarg.compare, e1._0, e2._0) !== 0) {
@@ -865,17 +870,17 @@ function Make(funarg) {
     };
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var bindings_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
diff --git a/lib/es6/mapLabels.js b/lib/es6/mapLabels.js
index b7fb0b8434..ff589eb094 100644
--- a/lib/es6/mapLabels.js
+++ b/lib/es6/mapLabels.js
@@ -5,10 +5,10 @@ import * as Caml_option from "./caml_option.js";
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, x, d, r) {
@@ -32,26 +32,28 @@ function Make(Ord) {
           };
   };
   var bal = function (l, x, d, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var ld = l.d;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, ld, create(lr, x, d, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var ld = l.d;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, ld, create(lr, x, d, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
@@ -67,23 +69,23 @@ function Make(Ord) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rd = r.d;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, x, d, rl), rv, rd, rr);
-      }
-      if (rl) {
-        return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rd = r.d;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, x, d, rl), rv, rd, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -91,14 +93,14 @@ function Make(Ord) {
         };
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var add = function (x, data, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -143,18 +145,18 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var c = Curry._2(Ord.compare, x, param.v);
-        if (c === 0) {
-          return param.d;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = Curry._2(Ord.compare, x, param.v);
+      if (c === 0) {
+        return param.d;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first_aux = function (_v0, _d0, f, _param) {
@@ -162,7 +164,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -182,18 +184,18 @@ function Make(Ord) {
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_first_aux(v, param.d, f, param.l);
-        }
-        _param = param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_first_aux(v, param.d, f, param.l);
+      }
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt_aux = function (_v0, _d0, f, _param) {
@@ -201,7 +203,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -221,7 +223,7 @@ function Make(Ord) {
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -237,7 +239,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -257,18 +259,18 @@ function Make(Ord) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_last_aux(v, param.d, f, param.r);
-        }
-        _param = param.l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_last_aux(v, param.d, f, param.r);
+      }
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt_aux = function (_v0, _d0, f, _param) {
@@ -276,7 +278,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -296,7 +298,7 @@ function Make(Ord) {
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -310,7 +312,7 @@ function Make(Ord) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -324,7 +326,7 @@ function Make(Ord) {
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -338,31 +340,31 @@ function Make(Ord) {
   var min_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return [
                 param.v,
                 param.d
@@ -375,31 +377,31 @@ function Make(Ord) {
   var max_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return [
                 param.v,
                 param.d
@@ -410,32 +412,32 @@ function Make(Ord) {
     };
   };
   var remove_min_binding = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_binding(l), param.v, param.d, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Map.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_binding(l), param.v, param.d, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
     return bal(t1, match[0], match[1], remove_min_binding(t2));
   };
   var remove = function (x, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -462,62 +464,62 @@ function Make(Ord) {
     }
   };
   var update = function (x, f, m) {
-    if (m) {
-      var r = m.r;
-      var d = m.d;
-      var v = m.v;
-      var l = m.l;
-      var c = Curry._2(Ord.compare, x, v);
-      if (c === 0) {
-        var data = Curry._1(f, Caml_option.some(d));
-        if (data === undefined) {
-          return merge(l, r);
-        }
-        var data$1 = Caml_option.valFromOption(data);
-        if (d === data$1) {
-          return m;
-        } else {
-          return /* Node */{
-                  l: l,
-                  v: x,
-                  d: data$1,
-                  r: r,
-                  h: m.h
-                };
-        }
+    if (/* tag */typeof m === "number") {
+      var data = Curry._1(f, undefined);
+      if (data !== undefined) {
+        return /* Node */{
+                l: /* Empty */0,
+                v: x,
+                d: Caml_option.valFromOption(data),
+                r: /* Empty */0,
+                h: 1
+              };
+      } else {
+        return /* Empty */0;
       }
-      if (c < 0) {
-        var ll = update(x, f, l);
-        if (l === ll) {
-          return m;
-        } else {
-          return bal(ll, v, d, r);
-        }
+    }
+    var r = m.r;
+    var d = m.d;
+    var v = m.v;
+    var l = m.l;
+    var c = Curry._2(Ord.compare, x, v);
+    if (c === 0) {
+      var data$1 = Curry._1(f, Caml_option.some(d));
+      if (data$1 === undefined) {
+        return merge(l, r);
       }
-      var rr = update(x, f, r);
-      if (r === rr) {
+      var data$2 = Caml_option.valFromOption(data$1);
+      if (d === data$2) {
         return m;
       } else {
-        return bal(l, v, d, rr);
+        return /* Node */{
+                l: l,
+                v: x,
+                d: data$2,
+                r: r,
+                h: m.h
+              };
       }
     }
-    var data$2 = Curry._1(f, undefined);
-    if (data$2 !== undefined) {
-      return /* Node */{
-              l: /* Empty */0,
-              v: x,
-              d: Caml_option.valFromOption(data$2),
-              r: /* Empty */0,
-              h: 1
-            };
+    if (c < 0) {
+      var ll = update(x, f, l);
+      if (l === ll) {
+        return m;
+      } else {
+        return bal(ll, v, d, r);
+      }
+    }
+    var rr = update(x, f, r);
+    if (r === rr) {
+      return m;
     } else {
-      return /* Empty */0;
+      return bal(l, v, d, rr);
     }
   };
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -527,7 +529,7 @@ function Make(Ord) {
     };
   };
   var map = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var l$p = map(f, param.l);
@@ -542,7 +544,7 @@ function Make(Ord) {
           };
   };
   var mapi = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param.v;
@@ -561,7 +563,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return accu;
       }
       _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -572,7 +574,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._2(p, param.v, param.d)) {
@@ -588,7 +590,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._2(p, param.v, param.d)) {
@@ -602,28 +604,28 @@ function Make(Ord) {
     };
   };
   var add_min_binding = function (k, x, param) {
-    if (param) {
-      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
     }
   };
   var add_max_binding = function (k, x, param) {
-    if (param) {
-      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
     }
   };
   var join = function (l, v, d, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_binding(v, d, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_binding(v, d, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, l.d, join(l.r, v, d, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -633,10 +635,10 @@ function Make(Ord) {
     }
   };
   var concat = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
@@ -650,7 +652,7 @@ function Make(Ord) {
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               undefined,
@@ -685,42 +687,45 @@ function Make(Ord) {
           ];
   };
   var merge$1 = function (f, s1, s2) {
-    if (s1) {
+    if (/* tag */typeof s1 === "number") {
+      if (/* tag */typeof s2 === "number") {
+        return /* Empty */0;
+      }
+      
+    } else {
       var v1 = s1.v;
       if (s1.h >= height(s2)) {
         var match = split(v1, s2);
         return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
       }
       
-    } else if (!s2) {
-      return /* Empty */0;
     }
-    if (s2) {
-      var v2 = s2.v;
-      var match$1 = split(v2, s1);
-      return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+    if (/* tag */typeof s2 === "number") {
+      throw {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "mapLabels.ml",
+              393,
+              10
+            ],
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "mapLabels.ml",
-            393,
-            10
-          ],
-          Error: new Error()
-        };
+    var v2 = s2.v;
+    var match$1 = split(v2, s1);
+    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   };
   var union = function (f, s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var d1 = s1.d;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var d2 = s2.d;
     var v2 = s2.v;
-    var d1 = s1.d;
-    var v1 = s1.v;
     if (s1.h >= s2.h) {
       var match = split(v1, s2);
       var d2$1 = match[1];
@@ -743,7 +748,7 @@ function Make(Ord) {
     }
   };
   var filter = function (p, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -764,7 +769,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -795,7 +800,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return e;
       }
       _e = /* More */{
@@ -814,14 +819,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -843,14 +848,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return false;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return true;
+        } else {
+          return false;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return false;
       }
       if (Curry._2(Ord.compare, e1._0, e2._0) !== 0) {
@@ -865,17 +870,17 @@ function Make(Ord) {
     };
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var bindings_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
diff --git a/lib/es6/moreLabels.js b/lib/es6/moreLabels.js
index 2fd0710a50..82b64f8f44 100644
--- a/lib/es6/moreLabels.js
+++ b/lib/es6/moreLabels.js
@@ -35,10 +35,10 @@ var Hashtbl = {
 var $$Map = {
   Make: (function (funarg) {
       var height = function (param) {
-        if (param) {
-          return param.h;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return param.h;
         }
       };
       var create = function (l, x, d, r) {
@@ -62,26 +62,28 @@ var $$Map = {
               };
       };
       var bal = function (l, x, d, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         if (hl > (hr + 2 | 0)) {
-          if (l) {
-            var lr = l.r;
-            var ld = l.d;
-            var lv = l.v;
-            var ll = l.l;
-            if (height(ll) >= height(lr)) {
-              return create(ll, lv, ld, create(lr, x, d, r));
-            }
-            if (lr) {
-              return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-            }
+          if (/* tag */typeof l === "number") {
             throw {
                   RE_EXN_ID: "Invalid_argument",
                   _1: "Map.bal",
                   Error: new Error()
                 };
           }
+          var lr = l.r;
+          var ld = l.d;
+          var lv = l.v;
+          var ll = l.l;
+          if (height(ll) >= height(lr)) {
+            return create(ll, lv, ld, create(lr, x, d, r));
+          }
+          if (/* tag */typeof lr !== "number") {
+            return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+          }
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Map.bal",
@@ -97,23 +99,23 @@ var $$Map = {
                   h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
                 };
         }
-        if (r) {
-          var rr = r.r;
-          var rd = r.d;
-          var rv = r.v;
-          var rl = r.l;
-          if (height(rr) >= height(rl)) {
-            return create(create(l, x, d, rl), rv, rd, rr);
-          }
-          if (rl) {
-            return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-          }
+        if (/* tag */typeof r === "number") {
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Map.bal",
                 Error: new Error()
               };
         }
+        var rr = r.r;
+        var rd = r.d;
+        var rv = r.v;
+        var rl = r.l;
+        if (height(rr) >= height(rl)) {
+          return create(create(l, x, d, rl), rv, rd, rr);
+        }
+        if (/* tag */typeof rl !== "number") {
+          return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+        }
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
@@ -121,14 +123,14 @@ var $$Map = {
             };
       };
       var is_empty = function (param) {
-        if (param) {
-          return false;
-        } else {
+        if (/* tag */typeof param === "number") {
           return true;
+        } else {
+          return false;
         }
       };
       var add = function (x, data, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Node */{
                   l: /* Empty */0,
                   v: x,
@@ -173,18 +175,18 @@ var $$Map = {
       var find = function (x, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var c = Curry._2(funarg.compare, x, param.v);
-            if (c === 0) {
-              return param.d;
-            }
-            _param = c < 0 ? param.l : param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var c = Curry._2(funarg.compare, x, param.v);
+          if (c === 0) {
+            return param.d;
+          }
+          _param = c < 0 ? param.l : param.r;
+          continue ;
         };
       };
       var find_first_aux = function (_v0, _d0, f, _param) {
@@ -192,7 +194,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -212,18 +214,18 @@ var $$Map = {
       var find_first = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_first_aux(v, param.d, f, param.l);
-            }
-            _param = param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_first_aux(v, param.d, f, param.l);
+          }
+          _param = param.r;
+          continue ;
         };
       };
       var find_first_opt_aux = function (_v0, _d0, f, _param) {
@@ -231,7 +233,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -251,7 +253,7 @@ var $$Map = {
       var find_first_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -267,7 +269,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -287,18 +289,18 @@ var $$Map = {
       var find_last = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_last_aux(v, param.d, f, param.r);
-            }
-            _param = param.l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_last_aux(v, param.d, f, param.r);
+          }
+          _param = param.l;
+          continue ;
         };
       };
       var find_last_opt_aux = function (_v0, _d0, f, _param) {
@@ -306,7 +308,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -326,7 +328,7 @@ var $$Map = {
       var find_last_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -340,7 +342,7 @@ var $$Map = {
       var find_opt = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -354,7 +356,7 @@ var $$Map = {
       var mem = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -368,31 +370,31 @@ var $$Map = {
       var min_binding = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var l = param.l;
-            if (!l) {
-              return [
-                      param.v,
-                      param.d
-                    ];
-            }
-            _param = l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var l = param.l;
+          if (/* tag */typeof l === "number") {
+            return [
+                    param.v,
+                    param.d
+                  ];
+          }
+          _param = l;
+          continue ;
         };
       };
       var min_binding_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var l = param.l;
-          if (!l) {
+          if (/* tag */typeof l === "number") {
             return [
                     param.v,
                     param.d
@@ -405,31 +407,31 @@ var $$Map = {
       var max_binding = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var r = param.r;
-            if (!r) {
-              return [
-                      param.v,
-                      param.d
-                    ];
-            }
-            _param = r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var r = param.r;
+          if (/* tag */typeof r === "number") {
+            return [
+                    param.v,
+                    param.d
+                  ];
+          }
+          _param = r;
+          continue ;
         };
       };
       var max_binding_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var r = param.r;
-          if (!r) {
+          if (/* tag */typeof r === "number") {
             return [
                     param.v,
                     param.d
@@ -440,32 +442,32 @@ var $$Map = {
         };
       };
       var remove_min_binding = function (param) {
-        if (param) {
-          var l = param.l;
-          if (l) {
-            return bal(remove_min_binding(l), param.v, param.d, param.r);
-          } else {
-            return param.r;
-          }
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Invalid_argument",
+                _1: "Map.remove_min_elt",
+                Error: new Error()
+              };
+        }
+        var l = param.l;
+        if (/* tag */typeof l === "number") {
+          return param.r;
+        } else {
+          return bal(remove_min_binding(l), param.v, param.d, param.r);
         }
-        throw {
-              RE_EXN_ID: "Invalid_argument",
-              _1: "Map.remove_min_elt",
-              Error: new Error()
-            };
       };
       var merge = function (t1, t2) {
-        if (!t1) {
+        if (/* tag */typeof t1 === "number") {
           return t2;
         }
-        if (!t2) {
+        if (/* tag */typeof t2 === "number") {
           return t1;
         }
         var match = min_binding(t2);
         return bal(t1, match[0], match[1], remove_min_binding(t2));
       };
       var remove = function (x, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Empty */0;
         }
         var r = m.r;
@@ -492,62 +494,62 @@ var $$Map = {
         }
       };
       var update = function (x, f, m) {
-        if (m) {
-          var r = m.r;
-          var d = m.d;
-          var v = m.v;
-          var l = m.l;
-          var c = Curry._2(funarg.compare, x, v);
-          if (c === 0) {
-            var data = Curry._1(f, Caml_option.some(d));
-            if (data === undefined) {
-              return merge(l, r);
-            }
-            var data$1 = Caml_option.valFromOption(data);
-            if (d === data$1) {
-              return m;
-            } else {
-              return /* Node */{
-                      l: l,
-                      v: x,
-                      d: data$1,
-                      r: r,
-                      h: m.h
-                    };
-            }
+        if (/* tag */typeof m === "number") {
+          var data = Curry._1(f, undefined);
+          if (data !== undefined) {
+            return /* Node */{
+                    l: /* Empty */0,
+                    v: x,
+                    d: Caml_option.valFromOption(data),
+                    r: /* Empty */0,
+                    h: 1
+                  };
+          } else {
+            return /* Empty */0;
           }
-          if (c < 0) {
-            var ll = update(x, f, l);
-            if (l === ll) {
-              return m;
-            } else {
-              return bal(ll, v, d, r);
-            }
+        }
+        var r = m.r;
+        var d = m.d;
+        var v = m.v;
+        var l = m.l;
+        var c = Curry._2(funarg.compare, x, v);
+        if (c === 0) {
+          var data$1 = Curry._1(f, Caml_option.some(d));
+          if (data$1 === undefined) {
+            return merge(l, r);
           }
-          var rr = update(x, f, r);
-          if (r === rr) {
+          var data$2 = Caml_option.valFromOption(data$1);
+          if (d === data$2) {
             return m;
           } else {
-            return bal(l, v, d, rr);
+            return /* Node */{
+                    l: l,
+                    v: x,
+                    d: data$2,
+                    r: r,
+                    h: m.h
+                  };
           }
         }
-        var data$2 = Curry._1(f, undefined);
-        if (data$2 !== undefined) {
-          return /* Node */{
-                  l: /* Empty */0,
-                  v: x,
-                  d: Caml_option.valFromOption(data$2),
-                  r: /* Empty */0,
-                  h: 1
-                };
+        if (c < 0) {
+          var ll = update(x, f, l);
+          if (l === ll) {
+            return m;
+          } else {
+            return bal(ll, v, d, r);
+          }
+        }
+        var rr = update(x, f, r);
+        if (r === rr) {
+          return m;
         } else {
-          return /* Empty */0;
+          return bal(l, v, d, rr);
         }
       };
       var iter = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           iter(f, param.l);
@@ -557,7 +559,7 @@ var $$Map = {
         };
       };
       var map = function (f, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* Empty */0;
         }
         var l$p = map(f, param.l);
@@ -572,7 +574,7 @@ var $$Map = {
               };
       };
       var mapi = function (f, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* Empty */0;
         }
         var v = param.v;
@@ -591,7 +593,7 @@ var $$Map = {
         while(true) {
           var accu = _accu;
           var m = _m;
-          if (!m) {
+          if (/* tag */typeof m === "number") {
             return accu;
           }
           _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -602,7 +604,7 @@ var $$Map = {
       var for_all = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return true;
           }
           if (!Curry._2(p, param.v, param.d)) {
@@ -618,7 +620,7 @@ var $$Map = {
       var exists = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           if (Curry._2(p, param.v, param.d)) {
@@ -632,28 +634,28 @@ var $$Map = {
         };
       };
       var add_min_binding = function (k, x, param) {
-        if (param) {
-          return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(k, x);
+        } else {
+          return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
         }
       };
       var add_max_binding = function (k, x, param) {
-        if (param) {
-          return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(k, x);
+        } else {
+          return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
         }
       };
       var join = function (l, v, d, r) {
-        if (!l) {
+        if (/* tag */typeof l === "number") {
           return add_min_binding(v, d, r);
         }
-        if (!r) {
+        var lh = l.h;
+        if (/* tag */typeof r === "number") {
           return add_max_binding(v, d, l);
         }
         var rh = r.h;
-        var lh = l.h;
         if (lh > (rh + 2 | 0)) {
           return bal(l.l, l.v, l.d, join(l.r, v, d, r));
         } else if (rh > (lh + 2 | 0)) {
@@ -663,10 +665,10 @@ var $$Map = {
         }
       };
       var concat = function (t1, t2) {
-        if (!t1) {
+        if (/* tag */typeof t1 === "number") {
           return t2;
         }
-        if (!t2) {
+        if (/* tag */typeof t2 === "number") {
           return t1;
         }
         var match = min_binding(t2);
@@ -680,7 +682,7 @@ var $$Map = {
         }
       };
       var split = function (x, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   undefined,
@@ -715,42 +717,45 @@ var $$Map = {
               ];
       };
       var merge$1 = function (f, s1, s2) {
-        if (s1) {
+        if (/* tag */typeof s1 === "number") {
+          if (/* tag */typeof s2 === "number") {
+            return /* Empty */0;
+          }
+          
+        } else {
           var v1 = s1.v;
           if (s1.h >= height(s2)) {
             var match = split(v1, s2);
             return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
           }
           
-        } else if (!s2) {
-          return /* Empty */0;
         }
-        if (s2) {
-          var v2 = s2.v;
-          var match$1 = split(v2, s1);
-          return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+        if (/* tag */typeof s2 === "number") {
+          throw {
+                RE_EXN_ID: "Assert_failure",
+                _1: [
+                  "mapLabels.ml",
+                  393,
+                  10
+                ],
+                Error: new Error()
+              };
         }
-        throw {
-              RE_EXN_ID: "Assert_failure",
-              _1: [
-                "mapLabels.ml",
-                393,
-                10
-              ],
-              Error: new Error()
-            };
+        var v2 = s2.v;
+        var match$1 = split(v2, s1);
+        return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
       };
       var union = function (f, s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return s2;
         }
-        if (!s2) {
+        var d1 = s1.d;
+        var v1 = s1.v;
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var d2 = s2.d;
         var v2 = s2.v;
-        var d1 = s1.d;
-        var v1 = s1.v;
         if (s1.h >= s2.h) {
           var match = split(v1, s2);
           var d2$1 = match[1];
@@ -773,7 +778,7 @@ var $$Map = {
         }
       };
       var filter = function (p, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Empty */0;
         }
         var r = m.r;
@@ -794,7 +799,7 @@ var $$Map = {
         }
       };
       var partition = function (p, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   /* Empty */0
@@ -825,7 +830,7 @@ var $$Map = {
         while(true) {
           var e = _e;
           var m = _m;
-          if (!m) {
+          if (/* tag */typeof m === "number") {
             return e;
           }
           _e = /* More */{
@@ -844,14 +849,14 @@ var $$Map = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return -1;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return 0;
+            } else {
+              return -1;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return 1;
           }
           var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -873,14 +878,14 @@ var $$Map = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return false;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return true;
+            } else {
+              return false;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return false;
           }
           if (Curry._2(funarg.compare, e1._0, e2._0) !== 0) {
@@ -895,17 +900,17 @@ var $$Map = {
         };
       };
       var cardinal = function (param) {
-        if (param) {
-          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
         }
       };
       var bindings_aux = function (_accu, _param) {
         while(true) {
           var param = _param;
           var accu = _accu;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return accu;
           }
           _param = param.l;
@@ -964,15 +969,17 @@ var $$Map = {
 var $$Set = {
   Make: (function (funarg) {
       var height = function (param) {
-        if (param) {
-          return param.h;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return param.h;
         }
       };
       var create = function (l, v, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         return /* Node */{
                 l: l,
                 v: v,
@@ -981,25 +988,27 @@ var $$Set = {
               };
       };
       var bal = function (l, v, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         if (hl > (hr + 2 | 0)) {
-          if (l) {
-            var lr = l.r;
-            var lv = l.v;
-            var ll = l.l;
-            if (height(ll) >= height(lr)) {
-              return create(ll, lv, create(lr, v, r));
-            }
-            if (lr) {
-              return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-            }
+          if (/* tag */typeof l === "number") {
             throw {
                   RE_EXN_ID: "Invalid_argument",
                   _1: "Set.bal",
                   Error: new Error()
                 };
           }
+          var lr = l.r;
+          var lv = l.v;
+          var ll = l.l;
+          if (height(ll) >= height(lr)) {
+            return create(ll, lv, create(lr, v, r));
+          }
+          if (/* tag */typeof lr !== "number") {
+            return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+          }
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Set.bal",
@@ -1014,22 +1023,22 @@ var $$Set = {
                   h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
                 };
         }
-        if (r) {
-          var rr = r.r;
-          var rv = r.v;
-          var rl = r.l;
-          if (height(rr) >= height(rl)) {
-            return create(create(l, v, rl), rv, rr);
-          }
-          if (rl) {
-            return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-          }
+        if (/* tag */typeof r === "number") {
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Set.bal",
                 Error: new Error()
               };
         }
+        var rr = r.r;
+        var rv = r.v;
+        var rl = r.l;
+        if (height(rr) >= height(rl)) {
+          return create(create(l, v, rl), rv, rr);
+        }
+        if (/* tag */typeof rl !== "number") {
+          return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+        }
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
@@ -1037,7 +1046,7 @@ var $$Set = {
             };
       };
       var add = function (x, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Node */{
                   l: /* Empty */0,
                   v: x,
@@ -1076,28 +1085,28 @@ var $$Set = {
               };
       };
       var add_min_element = function (x, param) {
-        if (param) {
-          return bal(add_min_element(x, param.l), param.v, param.r);
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(x);
+        } else {
+          return bal(add_min_element(x, param.l), param.v, param.r);
         }
       };
       var add_max_element = function (x, param) {
-        if (param) {
-          return bal(param.l, param.v, add_max_element(x, param.r));
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(x);
+        } else {
+          return bal(param.l, param.v, add_max_element(x, param.r));
         }
       };
       var join = function (l, v, r) {
-        if (!l) {
+        if (/* tag */typeof l === "number") {
           return add_min_element(v, r);
         }
-        if (!r) {
+        var lh = l.h;
+        if (/* tag */typeof r === "number") {
           return add_max_element(v, l);
         }
         var rh = r.h;
-        var lh = l.h;
         if (lh > (rh + 2 | 0)) {
           return bal(l.l, l.v, join(l.r, v, r));
         } else if (rh > (lh + 2 | 0)) {
@@ -1109,28 +1118,28 @@ var $$Set = {
       var min_elt = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var l = param.l;
-            if (!l) {
-              return param.v;
-            }
-            _param = l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var l = param.l;
+          if (/* tag */typeof l === "number") {
+            return param.v;
+          }
+          _param = l;
+          continue ;
         };
       };
       var min_elt_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var l = param.l;
-          if (!l) {
+          if (/* tag */typeof l === "number") {
             return Caml_option.some(param.v);
           }
           _param = l;
@@ -1140,28 +1149,28 @@ var $$Set = {
       var max_elt = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var r = param.r;
-            if (!r) {
-              return param.v;
-            }
-            _param = r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var r = param.r;
+          if (/* tag */typeof r === "number") {
+            return param.v;
+          }
+          _param = r;
+          continue ;
         };
       };
       var max_elt_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var r = param.r;
-          if (!r) {
+          if (/* tag */typeof r === "number") {
             return Caml_option.some(param.v);
           }
           _param = r;
@@ -1169,44 +1178,40 @@ var $$Set = {
         };
       };
       var remove_min_elt = function (param) {
-        if (param) {
-          var l = param.l;
-          if (l) {
-            return bal(remove_min_elt(l), param.v, param.r);
-          } else {
-            return param.r;
-          }
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Invalid_argument",
+                _1: "Set.remove_min_elt",
+                Error: new Error()
+              };
+        }
+        var l = param.l;
+        if (/* tag */typeof l === "number") {
+          return param.r;
+        } else {
+          return bal(remove_min_elt(l), param.v, param.r);
         }
-        throw {
-              RE_EXN_ID: "Invalid_argument",
-              _1: "Set.remove_min_elt",
-              Error: new Error()
-            };
       };
       var merge = function (t1, t2) {
-        if (t1) {
-          if (t2) {
-            return bal(t1, min_elt(t2), remove_min_elt(t2));
-          } else {
-            return t1;
-          }
-        } else {
+        if (/* tag */typeof t1 === "number") {
           return t2;
+        } else if (/* tag */typeof t2 === "number") {
+          return t1;
+        } else {
+          return bal(t1, min_elt(t2), remove_min_elt(t2));
         }
       };
       var concat = function (t1, t2) {
-        if (t1) {
-          if (t2) {
-            return join(t1, min_elt(t2), remove_min_elt(t2));
-          } else {
-            return t1;
-          }
-        } else {
+        if (/* tag */typeof t1 === "number") {
           return t2;
+        } else if (/* tag */typeof t2 === "number") {
+          return t1;
+        } else {
+          return join(t1, min_elt(t2), remove_min_elt(t2));
         }
       };
       var split = function (x, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   false,
@@ -1240,16 +1245,16 @@ var $$Set = {
               ];
       };
       var is_empty = function (param) {
-        if (param) {
-          return false;
-        } else {
+        if (/* tag */typeof param === "number") {
           return true;
+        } else {
+          return false;
         }
       };
       var mem = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -1261,7 +1266,7 @@ var $$Set = {
         };
       };
       var remove = function (x, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
@@ -1287,16 +1292,16 @@ var $$Set = {
         }
       };
       var union = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return s2;
         }
-        if (!s2) {
+        var h1 = s1.h;
+        var v1 = s1.v;
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var h2 = s2.h;
         var v2 = s2.v;
-        var h1 = s1.h;
-        var v1 = s1.v;
         if (h1 >= h2) {
           if (h2 === 1) {
             return add(v2, s1);
@@ -1311,10 +1316,10 @@ var $$Set = {
         return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
       };
       var inter = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return /* Empty */0;
         }
-        if (!s2) {
+        if (/* tag */typeof s2 === "number") {
           return /* Empty */0;
         }
         var r1 = s1.r;
@@ -1329,10 +1334,10 @@ var $$Set = {
         }
       };
       var diff = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return /* Empty */0;
         }
-        if (!s2) {
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var r1 = s1.r;
@@ -1350,7 +1355,7 @@ var $$Set = {
         while(true) {
           var e = _e;
           var s = _s;
-          if (!s) {
+          if (/* tag */typeof s === "number") {
             return e;
           }
           _e = /* More */{
@@ -1366,14 +1371,14 @@ var $$Set = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return -1;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return 0;
+            } else {
+              return -1;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return 1;
           }
           var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -1395,17 +1400,17 @@ var $$Set = {
         while(true) {
           var s2 = _s2;
           var s1 = _s1;
-          if (!s1) {
+          if (/* tag */typeof s1 === "number") {
             return true;
           }
-          if (!s2) {
+          var r1 = s1.r;
+          var v1 = s1.v;
+          var l1 = s1.l;
+          if (/* tag */typeof s2 === "number") {
             return false;
           }
           var r2 = s2.r;
           var l2 = s2.l;
-          var r1 = s1.r;
-          var v1 = s1.v;
-          var l1 = s1.l;
           var c = Curry._2(funarg.compare, v1, s2.v);
           if (c === 0) {
             if (!subset(l1, l2)) {
@@ -1442,7 +1447,7 @@ var $$Set = {
       var iter = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           iter(f, param.l);
@@ -1455,7 +1460,7 @@ var $$Set = {
         while(true) {
           var accu = _accu;
           var s = _s;
-          if (!s) {
+          if (/* tag */typeof s === "number") {
             return accu;
           }
           _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -1466,7 +1471,7 @@ var $$Set = {
       var for_all = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return true;
           }
           if (!Curry._1(p, param.v)) {
@@ -1482,7 +1487,7 @@ var $$Set = {
       var exists = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           if (Curry._1(p, param.v)) {
@@ -1496,7 +1501,7 @@ var $$Set = {
         };
       };
       var filter = function (p, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
@@ -1516,7 +1521,7 @@ var $$Set = {
         }
       };
       var partition = function (p, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   /* Empty */0
@@ -1543,17 +1548,17 @@ var $$Set = {
         }
       };
       var cardinal = function (param) {
-        if (param) {
-          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
         }
       };
       var elements_aux = function (_accu, _param) {
         while(true) {
           var param = _param;
           var accu = _accu;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return accu;
           }
           _param = param.l;
@@ -1570,26 +1575,26 @@ var $$Set = {
       var find = function (x, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            var c = Curry._2(funarg.compare, x, v);
-            if (c === 0) {
-              return v;
-            }
-            _param = c < 0 ? param.l : param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          var c = Curry._2(funarg.compare, x, v);
+          if (c === 0) {
+            return v;
+          }
+          _param = c < 0 ? param.l : param.r;
+          continue ;
         };
       };
       var find_first_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return v0;
           }
           var v = param.v;
@@ -1605,25 +1610,25 @@ var $$Set = {
       var find_first = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_first_aux(v, f, param.l);
-            }
-            _param = param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_first_aux(v, f, param.l);
+          }
+          _param = param.r;
+          continue ;
         };
       };
       var find_first_opt_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return Caml_option.some(v0);
           }
           var v = param.v;
@@ -1639,7 +1644,7 @@ var $$Set = {
       var find_first_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1654,7 +1659,7 @@ var $$Set = {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return v0;
           }
           var v = param.v;
@@ -1670,25 +1675,25 @@ var $$Set = {
       var find_last = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_last_aux(v, f, param.r);
-            }
-            _param = param.l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_last_aux(v, f, param.r);
+          }
+          _param = param.l;
+          continue ;
         };
       };
       var find_last_opt_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return Caml_option.some(v0);
           }
           var v = param.v;
@@ -1704,7 +1709,7 @@ var $$Set = {
       var find_last_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1718,7 +1723,7 @@ var $$Set = {
       var find_opt = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1738,7 +1743,7 @@ var $$Set = {
         }
       };
       var map = function (f, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
diff --git a/lib/es6/queue.js b/lib/es6/queue.js
index f81f9b0c91..e203fd819b 100644
--- a/lib/es6/queue.js
+++ b/lib/es6/queue.js
@@ -25,20 +25,20 @@ function add(x, q) {
     next: /* Nil */0
   };
   var last = q.last;
-  if (last) {
-    q.length = q.length + 1 | 0;
-    last.next = cell;
-    q.last = cell;
-  } else {
+  if (/* tag */typeof last === "number") {
     q.length = 1;
     q.first = cell;
     q.last = cell;
+    return ;
   }
+  q.length = q.length + 1 | 0;
+  last.next = cell;
+  q.last = cell;
 }
 
 function peek(q) {
   var match = q.first;
-  if (match) {
+  if (/* tag */typeof match !== "number") {
     return match.content;
   }
   throw {
@@ -49,22 +49,21 @@ function peek(q) {
 
 function take(q) {
   var match = q.first;
-  if (match) {
-    var content = match.content;
-    var next = match.next;
-    if (next) {
-      q.length = q.length - 1 | 0;
-      q.first = next;
-      return content;
-    } else {
-      clear(q);
-      return content;
-    }
+  if (/* tag */typeof match === "number") {
+    throw {
+          RE_EXN_ID: Empty,
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: Empty,
-        Error: new Error()
-      };
+  var content = match.content;
+  var next = match.next;
+  if (/* tag */typeof next === "number") {
+    clear(q);
+    return content;
+  }
+  q.length = q.length - 1 | 0;
+  q.first = next;
+  return content;
 }
 
 function copy(q) {
@@ -78,23 +77,23 @@ function copy(q) {
   while(true) {
     var cell = _cell;
     var prev = _prev;
-    if (cell) {
-      var next = cell.next;
-      var res = /* Cons */{
-        content: cell.content,
-        next: /* Nil */0
-      };
-      if (prev) {
-        prev.next = res;
-      } else {
-        q_res.first = res;
-      }
-      _cell = next;
-      _prev = res;
-      continue ;
+    if (/* tag */typeof cell === "number") {
+      q_res.last = prev;
+      return q_res;
+    }
+    var next = cell.next;
+    var res = /* Cons */{
+      content: cell.content,
+      next: /* Nil */0
+    };
+    if (/* tag */typeof prev === "number") {
+      q_res.first = res;
+    } else {
+      prev.next = res;
     }
-    q_res.last = prev;
-    return q_res;
+    _cell = next;
+    _prev = res;
+    continue ;
   };
 }
 
@@ -110,7 +109,7 @@ function iter(f, q) {
   var _cell = q.first;
   while(true) {
     var cell = _cell;
-    if (!cell) {
+    if (/* tag */typeof cell === "number") {
       return ;
     }
     var next = cell.next;
@@ -126,7 +125,7 @@ function fold(f, accu, q) {
   while(true) {
     var cell = _cell;
     var accu$1 = _accu;
-    if (!cell) {
+    if (/* tag */typeof cell === "number") {
       return accu$1;
     }
     var next = cell.next;
@@ -142,17 +141,16 @@ function transfer(q1, q2) {
     return ;
   }
   var last = q2.last;
-  if (last) {
-    q2.length = q2.length + q1.length | 0;
-    last.next = q1.first;
-    q2.last = q1.last;
-    return clear(q1);
-  } else {
+  if (/* tag */typeof last === "number") {
     q2.length = q1.length;
     q2.first = q1.first;
     q2.last = q1.last;
     return clear(q1);
   }
+  q2.length = q2.length + q1.length | 0;
+  last.next = q1.first;
+  q2.last = q1.last;
+  clear(q1);
 }
 
 var push = add;
diff --git a/lib/es6/set.js b/lib/es6/set.js
index 6a83dfcca1..b55bc25bec 100644
--- a/lib/es6/set.js
+++ b/lib/es6/set.js
@@ -6,15 +6,17 @@ import * as Caml_option from "./caml_option.js";
 
 function Make(funarg) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     return /* Node */{
             l: l,
             v: v,
@@ -23,25 +25,27 @@ function Make(funarg) {
           };
   };
   var bal = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, create(lr, v, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, create(lr, v, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
@@ -56,22 +60,22 @@ function Make(funarg) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, v, rl), rv, rr);
-      }
-      if (rl) {
-        return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, v, rl), rv, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -79,7 +83,7 @@ function Make(funarg) {
         };
   };
   var add = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -118,28 +122,28 @@ function Make(funarg) {
           };
   };
   var add_min_element = function (x, param) {
-    if (param) {
-      return bal(add_min_element(x, param.l), param.v, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(add_min_element(x, param.l), param.v, param.r);
     }
   };
   var add_max_element = function (x, param) {
-    if (param) {
-      return bal(param.l, param.v, add_max_element(x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(param.l, param.v, add_max_element(x, param.r));
     }
   };
   var join = function (l, v, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_element(v, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_element(v, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, join(l.r, v, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -151,28 +155,28 @@ function Make(funarg) {
   var min_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return param.v;
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return param.v;
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return Caml_option.some(param.v);
       }
       _param = l;
@@ -182,28 +186,28 @@ function Make(funarg) {
   var max_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return param.v;
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return param.v;
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return Caml_option.some(param.v);
       }
       _param = r;
@@ -211,33 +215,31 @@ function Make(funarg) {
     };
   };
   var remove_min_elt = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_elt(l), param.v, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Set.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_elt(l), param.v, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
   };
   var concat = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return join(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return join(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               false,
@@ -271,16 +273,16 @@ function Make(funarg) {
           ];
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -292,7 +294,7 @@ function Make(funarg) {
     };
   };
   var remove = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -300,14 +302,12 @@ function Make(funarg) {
     var l = t.l;
     var c = Curry._2(funarg.compare, x, v);
     if (c === 0) {
-      if (l) {
-        if (r) {
-          return bal(l, min_elt(r), remove_min_elt(r));
-        } else {
-          return l;
-        }
-      } else {
+      if (/* tag */typeof l === "number") {
         return r;
+      } else if (/* tag */typeof r === "number") {
+        return l;
+      } else {
+        return bal(l, min_elt(r), remove_min_elt(r));
       }
     }
     if (c < 0) {
@@ -326,16 +326,16 @@ function Make(funarg) {
     }
   };
   var union = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var h1 = s1.h;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var h2 = s2.h;
     var v2 = s2.v;
-    var h1 = s1.h;
-    var v1 = s1.v;
     if (h1 >= h2) {
       if (h2 === 1) {
         return add(v2, s1);
@@ -350,10 +350,10 @@ function Make(funarg) {
     return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
   };
   var inter = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return /* Empty */0;
     }
     var r1 = s1.r;
@@ -368,10 +368,10 @@ function Make(funarg) {
     }
   };
   var diff = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var r1 = s1.r;
@@ -389,7 +389,7 @@ function Make(funarg) {
     while(true) {
       var e = _e;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return e;
       }
       _e = /* More */{
@@ -407,14 +407,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -433,17 +433,17 @@ function Make(funarg) {
     while(true) {
       var s2 = _s2;
       var s1 = _s1;
-      if (!s1) {
+      if (/* tag */typeof s1 === "number") {
         return true;
       }
-      if (!s2) {
+      var r1 = s1.r;
+      var v1 = s1.v;
+      var l1 = s1.l;
+      if (/* tag */typeof s2 === "number") {
         return false;
       }
       var r2 = s2.r;
       var l2 = s2.l;
-      var r1 = s1.r;
-      var v1 = s1.v;
-      var l1 = s1.l;
       var c = Curry._2(funarg.compare, v1, s2.v);
       if (c === 0) {
         if (!subset(l1, l2)) {
@@ -480,7 +480,7 @@ function Make(funarg) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -493,7 +493,7 @@ function Make(funarg) {
     while(true) {
       var accu = _accu;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return accu;
       }
       _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -504,7 +504,7 @@ function Make(funarg) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._1(p, param.v)) {
@@ -520,7 +520,7 @@ function Make(funarg) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._1(p, param.v)) {
@@ -534,7 +534,7 @@ function Make(funarg) {
     };
   };
   var filter = function (p, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -554,7 +554,7 @@ function Make(funarg) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -581,17 +581,17 @@ function Make(funarg) {
     }
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var elements_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
@@ -608,58 +608,58 @@ function Make(funarg) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        var c = Curry._2(funarg.compare, x, v);
-        if (c === 0) {
-          return v;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      var c = Curry._2(funarg.compare, x, v);
+      if (c === 0) {
+        return v;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _param$1 = param.l;
-          while(true) {
-            var param$1 = _param$1;
-            var v0 = _v0;
-            if (!param$1) {
-              return v0;
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.l;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.r;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _param$1 = param.l;
+        while(true) {
+          var param$1 = _param$1;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return v0;
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.l;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.r;
-        continue ;
+          }
+          _param$1 = param$1.r;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -669,7 +669,7 @@ function Make(funarg) {
         while(true) {
           var param$1 = _param$1;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return Caml_option.some(v0);
           }
           var v$1 = param$1.v;
@@ -689,40 +689,40 @@ function Make(funarg) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _param$1 = param.r;
-          while(true) {
-            var param$1 = _param$1;
-            var v0 = _v0;
-            if (!param$1) {
-              return v0;
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.r;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.l;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _param$1 = param.r;
+        while(true) {
+          var param$1 = _param$1;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return v0;
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.r;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.l;
-        continue ;
+          }
+          _param$1 = param$1.l;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -732,7 +732,7 @@ function Make(funarg) {
         while(true) {
           var param$1 = _param$1;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return Caml_option.some(v0);
           }
           var v$1 = param$1.v;
@@ -752,7 +752,7 @@ function Make(funarg) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -765,7 +765,7 @@ function Make(funarg) {
     };
   };
   var map = function (f, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
diff --git a/lib/es6/setLabels.js b/lib/es6/setLabels.js
index 0b4f25ce72..cac3e77dc1 100644
--- a/lib/es6/setLabels.js
+++ b/lib/es6/setLabels.js
@@ -6,15 +6,17 @@ import * as Caml_option from "./caml_option.js";
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     return /* Node */{
             l: l,
             v: v,
@@ -23,25 +25,27 @@ function Make(Ord) {
           };
   };
   var bal = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, create(lr, v, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, create(lr, v, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
@@ -56,22 +60,22 @@ function Make(Ord) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, v, rl), rv, rr);
-      }
-      if (rl) {
-        return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, v, rl), rv, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -79,7 +83,7 @@ function Make(Ord) {
         };
   };
   var add = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -118,28 +122,28 @@ function Make(Ord) {
           };
   };
   var add_min_element = function (x, param) {
-    if (param) {
-      return bal(add_min_element(x, param.l), param.v, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(add_min_element(x, param.l), param.v, param.r);
     }
   };
   var add_max_element = function (x, param) {
-    if (param) {
-      return bal(param.l, param.v, add_max_element(x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(param.l, param.v, add_max_element(x, param.r));
     }
   };
   var join = function (l, v, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_element(v, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_element(v, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, join(l.r, v, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -151,28 +155,28 @@ function Make(Ord) {
   var min_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return param.v;
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return param.v;
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return Caml_option.some(param.v);
       }
       _param = l;
@@ -182,28 +186,28 @@ function Make(Ord) {
   var max_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return param.v;
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return param.v;
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return Caml_option.some(param.v);
       }
       _param = r;
@@ -211,44 +215,40 @@ function Make(Ord) {
     };
   };
   var remove_min_elt = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_elt(l), param.v, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Set.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_elt(l), param.v, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return bal(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return bal(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var concat = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return join(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return join(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               false,
@@ -282,16 +282,16 @@ function Make(Ord) {
           ];
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -303,7 +303,7 @@ function Make(Ord) {
     };
   };
   var remove = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -329,16 +329,16 @@ function Make(Ord) {
     }
   };
   var union = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var h1 = s1.h;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var h2 = s2.h;
     var v2 = s2.v;
-    var h1 = s1.h;
-    var v1 = s1.v;
     if (h1 >= h2) {
       if (h2 === 1) {
         return add(v2, s1);
@@ -353,10 +353,10 @@ function Make(Ord) {
     return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
   };
   var inter = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return /* Empty */0;
     }
     var r1 = s1.r;
@@ -371,10 +371,10 @@ function Make(Ord) {
     }
   };
   var diff = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var r1 = s1.r;
@@ -392,7 +392,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return e;
       }
       _e = /* More */{
@@ -408,14 +408,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -437,17 +437,17 @@ function Make(Ord) {
     while(true) {
       var s2 = _s2;
       var s1 = _s1;
-      if (!s1) {
+      if (/* tag */typeof s1 === "number") {
         return true;
       }
-      if (!s2) {
+      var r1 = s1.r;
+      var v1 = s1.v;
+      var l1 = s1.l;
+      if (/* tag */typeof s2 === "number") {
         return false;
       }
       var r2 = s2.r;
       var l2 = s2.l;
-      var r1 = s1.r;
-      var v1 = s1.v;
-      var l1 = s1.l;
       var c = Curry._2(Ord.compare, v1, s2.v);
       if (c === 0) {
         if (!subset(l1, l2)) {
@@ -484,7 +484,7 @@ function Make(Ord) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -497,7 +497,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return accu;
       }
       _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -508,7 +508,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._1(p, param.v)) {
@@ -524,7 +524,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._1(p, param.v)) {
@@ -538,7 +538,7 @@ function Make(Ord) {
     };
   };
   var filter = function (p, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -558,7 +558,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -585,17 +585,17 @@ function Make(Ord) {
     }
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var elements_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
@@ -612,26 +612,26 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        var c = Curry._2(Ord.compare, x, v);
-        if (c === 0) {
-          return v;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      var c = Curry._2(Ord.compare, x, v);
+      if (c === 0) {
+        return v;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return v0;
       }
       var v = param.v;
@@ -647,25 +647,25 @@ function Make(Ord) {
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_first_aux(v, f, param.l);
-        }
-        _param = param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_first_aux(v, f, param.l);
+      }
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return Caml_option.some(v0);
       }
       var v = param.v;
@@ -681,7 +681,7 @@ function Make(Ord) {
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -696,7 +696,7 @@ function Make(Ord) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return v0;
       }
       var v = param.v;
@@ -712,25 +712,25 @@ function Make(Ord) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_last_aux(v, f, param.r);
-        }
-        _param = param.l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_last_aux(v, f, param.r);
+      }
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return Caml_option.some(v0);
       }
       var v = param.v;
@@ -746,7 +746,7 @@ function Make(Ord) {
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -760,7 +760,7 @@ function Make(Ord) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -780,7 +780,7 @@ function Make(Ord) {
     }
   };
   var map = function (f, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
diff --git a/lib/es6/stream.js b/lib/es6/stream.js
index c1eb722914..4df812b1ae 100644
--- a/lib/es6/stream.js
+++ b/lib/es6/stream.js
@@ -31,7 +31,7 @@ function data(param) {
 function get_data(count, _d) {
   while(true) {
     var d = _d;
-    if (typeof d === "number") {
+    if (/* tag */typeof d === "number") {
       return d;
     }
     switch (d.TAG | 0) {
@@ -40,7 +40,7 @@ function get_data(count, _d) {
       case /* Sapp */1 :
           var d2 = d._1;
           var match = get_data(count, d._0);
-          if (typeof match === "number") {
+          if (/* tag */typeof match === "number") {
             _d = d2;
             continue ;
           }
@@ -102,7 +102,7 @@ function get_data(count, _d) {
 function peek_data(s) {
   while(true) {
     var f = s.data;
-    if (typeof f === "number") {
+    if (/* tag */typeof f === "number") {
       return ;
     }
     switch (f.TAG | 0) {
@@ -110,7 +110,7 @@ function peek_data(s) {
           return Caml_option.some(f._0);
       case /* Sapp */1 :
           var d = get_data(s.count, s.data);
-          if (typeof d === "number") {
+          if (/* tag */typeof d === "number") {
             return ;
           }
           if (d.TAG === /* Scons */0) {
@@ -153,7 +153,7 @@ function peek(s) {
 function junk_data(s) {
   while(true) {
     var g = s.data;
-    if (typeof g !== "number") {
+    if (/* tag */typeof g !== "number") {
       switch (g.TAG | 0) {
         case /* Scons */0 :
             s.count = s.count + 1 | 0;
@@ -428,7 +428,7 @@ function slazy(f) {
 }
 
 function dump_data(f, param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     console.log("Sempty");
     return ;
   }
diff --git a/lib/js/caml_module.js b/lib/js/caml_module.js
index db178b5731..f6f712ed81 100644
--- a/lib/js/caml_module.js
+++ b/lib/js/caml_module.js
@@ -11,7 +11,7 @@ function init_mod(loc, shape) {
         };
   };
   var loop = function (shape, struct_, idx) {
-    if (typeof shape === "number") {
+    if (/* tag */typeof shape === "number") {
       switch (shape) {
         case /* Function */0 :
             struct_[idx] = undef_module;
@@ -56,7 +56,7 @@ function init_mod(loc, shape) {
 
 function update_mod(shape, o, n) {
   var aux = function (shape, o, n, parent, i) {
-    if (typeof shape === "number") {
+    if (/* tag */typeof shape === "number") {
       switch (shape) {
         case /* Function */0 :
             parent[i] = n;
@@ -79,7 +79,7 @@ function update_mod(shape, o, n) {
       return ;
     }
   };
-  if (typeof shape === "number") {
+  if (/* tag */typeof shape === "number") {
     throw {
           RE_EXN_ID: "Assert_failure",
           _1: [
diff --git a/lib/js/hashtbl.js b/lib/js/hashtbl.js
index 8c52241161..81700f257a 100644
--- a/lib/js/hashtbl.js
+++ b/lib/js/hashtbl.js
@@ -92,7 +92,7 @@ function reset(h) {
 }
 
 function copy_bucketlist(param) {
-  if (!param) {
+  if (/* tag */typeof param === "number") {
     return /* Empty */0;
   }
   var key = param.key;
@@ -102,7 +102,7 @@ function copy_bucketlist(param) {
     while(true) {
       var param = _param;
       var prec = _prec;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var key = param.key;
@@ -113,9 +113,7 @@ function copy_bucketlist(param) {
         data: data,
         next: next
       };
-      if (prec) {
-        prec.next = r;
-      } else {
+      if (/* tag */typeof prec === "number") {
         throw {
               RE_EXN_ID: "Assert_failure",
               _1: [
@@ -126,6 +124,7 @@ function copy_bucketlist(param) {
               Error: new Error()
             };
       }
+      prec.next = r;
       _param = next;
       _prec = r;
       continue ;
@@ -167,7 +166,7 @@ function resize(indexfun, h) {
   var insert_bucket = function (_cell) {
     while(true) {
       var cell = _cell;
-      if (!cell) {
+      if (/* tag */typeof cell === "number") {
         return ;
       }
       var key = cell.key;
@@ -180,10 +179,10 @@ function resize(indexfun, h) {
           });
       var nidx = Curry._2(indexfun, h, key);
       var tail = Caml_array.get(ndata_tail, nidx);
-      if (tail) {
-        tail.next = cell$1;
-      } else {
+      if (/* tag */typeof tail === "number") {
         Caml_array.set(ndata, nidx, cell$1);
+      } else {
+        tail.next = cell$1;
       }
       Caml_array.set(ndata_tail, nidx, cell$1);
       _cell = next;
@@ -198,7 +197,7 @@ function resize(indexfun, h) {
   }
   for(var i$1 = 0; i$1 < nsize; ++i$1){
     var tail = Caml_array.get(ndata_tail, i$1);
-    if (tail) {
+    if (/* tag */typeof tail !== "number") {
       tail.next = /* Empty */0;
     }
     
@@ -231,18 +230,18 @@ function remove(h, key) {
   while(true) {
     var c = _c;
     var prec = _prec;
-    if (!c) {
+    if (/* tag */typeof c === "number") {
       return ;
     }
     var k = c.key;
     var next = c.next;
     if (Caml_obj.equal(k, key)) {
       h.size = h.size - 1 | 0;
-      if (prec) {
+      if (/* tag */typeof prec === "number") {
+        return Caml_array.set(h.data, i, next);
+      } else {
         prec.next = next;
         return ;
-      } else {
-        return Caml_array.set(h.data, i, next);
       }
     }
     _c = next;
@@ -253,66 +252,66 @@ function remove(h, key) {
 
 function find(h, key) {
   var match = Caml_array.get(h.data, key_index(h, key));
-  if (match) {
-    var k1 = match.key;
-    var d1 = match.data;
-    var next1 = match.next;
-    if (Caml_obj.equal(key, k1)) {
-      return d1;
-    }
-    if (next1) {
-      var k2 = next1.key;
-      var d2 = next1.data;
-      var next2 = next1.next;
-      if (Caml_obj.equal(key, k2)) {
-        return d2;
-      }
-      if (next2) {
-        var k3 = next2.key;
-        var d3 = next2.data;
-        var next3 = next2.next;
-        if (Caml_obj.equal(key, k3)) {
-          return d3;
-        } else {
-          var _param = next3;
-          while(true) {
-            var param = _param;
-            if (param) {
-              var k = param.key;
-              var data = param.data;
-              var next = param.next;
-              if (Caml_obj.equal(key, k)) {
-                return data;
-              }
-              _param = next;
-              continue ;
-            }
-            throw {
-                  RE_EXN_ID: "Not_found",
-                  Error: new Error()
-                };
-          };
-        }
-      }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
-    }
+  if (/* tag */typeof match === "number") {
     throw {
           RE_EXN_ID: "Not_found",
           Error: new Error()
         };
   }
-  throw {
-        RE_EXN_ID: "Not_found",
-        Error: new Error()
-      };
+  var k1 = match.key;
+  var d1 = match.data;
+  var next1 = match.next;
+  if (Caml_obj.equal(key, k1)) {
+    return d1;
+  }
+  if (/* tag */typeof next1 === "number") {
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
+  }
+  var k2 = next1.key;
+  var d2 = next1.data;
+  var next2 = next1.next;
+  if (Caml_obj.equal(key, k2)) {
+    return d2;
+  }
+  if (/* tag */typeof next2 === "number") {
+    throw {
+          RE_EXN_ID: "Not_found",
+          Error: new Error()
+        };
+  }
+  var k3 = next2.key;
+  var d3 = next2.data;
+  var next3 = next2.next;
+  if (Caml_obj.equal(key, k3)) {
+    return d3;
+  } else {
+    var _param = next3;
+    while(true) {
+      var param = _param;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var k = param.key;
+      var data = param.data;
+      var next = param.next;
+      if (Caml_obj.equal(key, k)) {
+        return data;
+      }
+      _param = next;
+      continue ;
+    };
+  }
 }
 
 function find_opt(h, key) {
   var match = Caml_array.get(h.data, key_index(h, key));
-  if (!match) {
+  if (/* tag */typeof match === "number") {
     return ;
   }
   var k1 = match.key;
@@ -321,7 +320,7 @@ function find_opt(h, key) {
   if (Caml_obj.equal(key, k1)) {
     return Caml_option.some(d1);
   }
-  if (!next1) {
+  if (/* tag */typeof next1 === "number") {
     return ;
   }
   var k2 = next1.key;
@@ -330,7 +329,7 @@ function find_opt(h, key) {
   if (Caml_obj.equal(key, k2)) {
     return Caml_option.some(d2);
   }
-  if (!next2) {
+  if (/* tag */typeof next2 === "number") {
     return ;
   }
   var k3 = next2.key;
@@ -342,7 +341,7 @@ function find_opt(h, key) {
     var _param = next3;
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var k = param.key;
@@ -361,7 +360,7 @@ function find_all(h, key) {
   var find_in_bucket = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return /* [] */0;
       }
       var k = param.key;
@@ -383,7 +382,7 @@ function find_all(h, key) {
 function replace_bucket(key, data, _slot) {
   while(true) {
     var slot = _slot;
-    if (!slot) {
+    if (/* tag */typeof slot === "number") {
       return true;
     }
     var k = slot.key;
@@ -421,7 +420,7 @@ function mem(h, key) {
   var _param = Caml_array.get(h.data, key_index(h, key));
   while(true) {
     var param = _param;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return false;
     }
     var k = param.key;
@@ -438,7 +437,7 @@ function iter(f, h) {
   var do_bucket = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var key = param.key;
@@ -477,12 +476,12 @@ function filter_map_inplace_bucket(f, h, i, _prec, _slot) {
   while(true) {
     var slot = _slot;
     var prec = _prec;
-    if (!slot) {
-      if (prec) {
+    if (/* tag */typeof slot === "number") {
+      if (/* tag */typeof prec === "number") {
+        return Caml_array.set(h.data, i, /* Empty */0);
+      } else {
         prec.next = /* Empty */0;
         return ;
-      } else {
-        return Caml_array.set(h.data, i, /* Empty */0);
       }
     }
     var key = slot.key;
@@ -490,10 +489,10 @@ function filter_map_inplace_bucket(f, h, i, _prec, _slot) {
     var next = slot.next;
     var data$1 = Curry._2(f, key, data);
     if (data$1 !== undefined) {
-      if (prec) {
-        prec.next = slot;
-      } else {
+      if (/* tag */typeof prec === "number") {
         Caml_array.set(h.data, i, slot);
+      } else {
+        prec.next = slot;
       }
       slot.data = Caml_option.valFromOption(data$1);
       _slot = next;
@@ -532,7 +531,7 @@ function fold(f, h, init) {
     while(true) {
       var accu = _accu;
       var b = _b;
-      if (!b) {
+      if (/* tag */typeof b === "number") {
         return accu;
       }
       var key = b.key;
@@ -571,7 +570,7 @@ function bucket_length(_accu, _param) {
   while(true) {
     var param = _param;
     var accu = _accu;
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return accu;
     }
     var next = param.next;
@@ -623,18 +622,18 @@ function MakeSeeded(H) {
     while(true) {
       var c = _c;
       var prec = _prec;
-      if (!c) {
+      if (/* tag */typeof c === "number") {
         return ;
       }
       var k = c.key;
       var next = c.next;
       if (Curry._2(H.equal, k, key)) {
         h.size = h.size - 1 | 0;
-        if (prec) {
+        if (/* tag */typeof prec === "number") {
+          return Caml_array.set(h.data, i, next);
+        } else {
           prec.next = next;
           return ;
-        } else {
-          return Caml_array.set(h.data, i, next);
         }
       }
       _c = next;
@@ -644,65 +643,65 @@ function MakeSeeded(H) {
   };
   var find = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (match) {
-      var k1 = match.key;
-      var d1 = match.data;
-      var next1 = match.next;
-      if (Curry._2(H.equal, key, k1)) {
-        return d1;
-      }
-      if (next1) {
-        var k2 = next1.key;
-        var d2 = next1.data;
-        var next2 = next1.next;
-        if (Curry._2(H.equal, key, k2)) {
-          return d2;
-        }
-        if (next2) {
-          var k3 = next2.key;
-          var d3 = next2.data;
-          var next3 = next2.next;
-          if (Curry._2(H.equal, key, k3)) {
-            return d3;
-          } else {
-            var _param = next3;
-            while(true) {
-              var param = _param;
-              if (param) {
-                var k = param.key;
-                var data = param.data;
-                var next = param.next;
-                if (Curry._2(H.equal, key, k)) {
-                  return data;
-                }
-                _param = next;
-                continue ;
-              }
-              throw {
-                    RE_EXN_ID: "Not_found",
-                    Error: new Error()
-                  };
-            };
-          }
-        }
-        throw {
-              RE_EXN_ID: "Not_found",
-              Error: new Error()
-            };
-      }
+    if (/* tag */typeof match === "number") {
       throw {
             RE_EXN_ID: "Not_found",
             Error: new Error()
           };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var k1 = match.key;
+    var d1 = match.data;
+    var next1 = match.next;
+    if (Curry._2(H.equal, key, k1)) {
+      return d1;
+    }
+    if (/* tag */typeof next1 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k2 = next1.key;
+    var d2 = next1.data;
+    var next2 = next1.next;
+    if (Curry._2(H.equal, key, k2)) {
+      return d2;
+    }
+    if (/* tag */typeof next2 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k3 = next2.key;
+    var d3 = next2.data;
+    var next3 = next2.next;
+    if (Curry._2(H.equal, key, k3)) {
+      return d3;
+    } else {
+      var _param = next3;
+      while(true) {
+        var param = _param;
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Not_found",
+                Error: new Error()
+              };
+        }
+        var k = param.key;
+        var data = param.data;
+        var next = param.next;
+        if (Curry._2(H.equal, key, k)) {
+          return data;
+        }
+        _param = next;
+        continue ;
+      };
+    }
   };
   var find_opt = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (!match) {
+    if (/* tag */typeof match === "number") {
       return ;
     }
     var k1 = match.key;
@@ -711,7 +710,7 @@ function MakeSeeded(H) {
     if (Curry._2(H.equal, key, k1)) {
       return Caml_option.some(d1);
     }
-    if (!next1) {
+    if (/* tag */typeof next1 === "number") {
       return ;
     }
     var k2 = next1.key;
@@ -720,7 +719,7 @@ function MakeSeeded(H) {
     if (Curry._2(H.equal, key, k2)) {
       return Caml_option.some(d2);
     }
-    if (!next2) {
+    if (/* tag */typeof next2 === "number") {
       return ;
     }
     var k3 = next2.key;
@@ -732,7 +731,7 @@ function MakeSeeded(H) {
       var _param = next3;
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return ;
         }
         var k = param.key;
@@ -750,7 +749,7 @@ function MakeSeeded(H) {
     var find_in_bucket = function (_param) {
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* [] */0;
         }
         var k = param.key;
@@ -771,7 +770,7 @@ function MakeSeeded(H) {
   var replace_bucket = function (key, data, _slot) {
     while(true) {
       var slot = _slot;
-      if (!slot) {
+      if (/* tag */typeof slot === "number") {
         return true;
       }
       var k = slot.key;
@@ -807,7 +806,7 @@ function MakeSeeded(H) {
     var _param = Caml_array.get(h.data, key_index(h, key));
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var k = param.key;
@@ -865,18 +864,18 @@ function Make(H) {
     while(true) {
       var c = _c;
       var prec = _prec;
-      if (!c) {
+      if (/* tag */typeof c === "number") {
         return ;
       }
       var k = c.key;
       var next = c.next;
       if (Curry._2(equal, k, key)) {
         h.size = h.size - 1 | 0;
-        if (prec) {
+        if (/* tag */typeof prec === "number") {
+          return Caml_array.set(h.data, i, next);
+        } else {
           prec.next = next;
           return ;
-        } else {
-          return Caml_array.set(h.data, i, next);
         }
       }
       _c = next;
@@ -886,65 +885,65 @@ function Make(H) {
   };
   var find = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (match) {
-      var k1 = match.key;
-      var d1 = match.data;
-      var next1 = match.next;
-      if (Curry._2(equal, key, k1)) {
-        return d1;
-      }
-      if (next1) {
-        var k2 = next1.key;
-        var d2 = next1.data;
-        var next2 = next1.next;
-        if (Curry._2(equal, key, k2)) {
-          return d2;
-        }
-        if (next2) {
-          var k3 = next2.key;
-          var d3 = next2.data;
-          var next3 = next2.next;
-          if (Curry._2(equal, key, k3)) {
-            return d3;
-          } else {
-            var _param = next3;
-            while(true) {
-              var param = _param;
-              if (param) {
-                var k = param.key;
-                var data = param.data;
-                var next = param.next;
-                if (Curry._2(equal, key, k)) {
-                  return data;
-                }
-                _param = next;
-                continue ;
-              }
-              throw {
-                    RE_EXN_ID: "Not_found",
-                    Error: new Error()
-                  };
-            };
-          }
-        }
-        throw {
-              RE_EXN_ID: "Not_found",
-              Error: new Error()
-            };
-      }
+    if (/* tag */typeof match === "number") {
       throw {
             RE_EXN_ID: "Not_found",
             Error: new Error()
           };
     }
-    throw {
-          RE_EXN_ID: "Not_found",
-          Error: new Error()
-        };
+    var k1 = match.key;
+    var d1 = match.data;
+    var next1 = match.next;
+    if (Curry._2(equal, key, k1)) {
+      return d1;
+    }
+    if (/* tag */typeof next1 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k2 = next1.key;
+    var d2 = next1.data;
+    var next2 = next1.next;
+    if (Curry._2(equal, key, k2)) {
+      return d2;
+    }
+    if (/* tag */typeof next2 === "number") {
+      throw {
+            RE_EXN_ID: "Not_found",
+            Error: new Error()
+          };
+    }
+    var k3 = next2.key;
+    var d3 = next2.data;
+    var next3 = next2.next;
+    if (Curry._2(equal, key, k3)) {
+      return d3;
+    } else {
+      var _param = next3;
+      while(true) {
+        var param = _param;
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Not_found",
+                Error: new Error()
+              };
+        }
+        var k = param.key;
+        var data = param.data;
+        var next = param.next;
+        if (Curry._2(equal, key, k)) {
+          return data;
+        }
+        _param = next;
+        continue ;
+      };
+    }
   };
   var find_opt = function (h, key) {
     var match = Caml_array.get(h.data, key_index(h, key));
-    if (!match) {
+    if (/* tag */typeof match === "number") {
       return ;
     }
     var k1 = match.key;
@@ -953,7 +952,7 @@ function Make(H) {
     if (Curry._2(equal, key, k1)) {
       return Caml_option.some(d1);
     }
-    if (!next1) {
+    if (/* tag */typeof next1 === "number") {
       return ;
     }
     var k2 = next1.key;
@@ -962,7 +961,7 @@ function Make(H) {
     if (Curry._2(equal, key, k2)) {
       return Caml_option.some(d2);
     }
-    if (!next2) {
+    if (/* tag */typeof next2 === "number") {
       return ;
     }
     var k3 = next2.key;
@@ -974,7 +973,7 @@ function Make(H) {
       var _param = next3;
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return ;
         }
         var k = param.key;
@@ -992,7 +991,7 @@ function Make(H) {
     var find_in_bucket = function (_param) {
       while(true) {
         var param = _param;
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* [] */0;
         }
         var k = param.key;
@@ -1013,7 +1012,7 @@ function Make(H) {
   var replace_bucket = function (key, data, _slot) {
     while(true) {
       var slot = _slot;
-      if (!slot) {
+      if (/* tag */typeof slot === "number") {
         return true;
       }
       var k = slot.key;
@@ -1049,7 +1048,7 @@ function Make(H) {
     var _param = Caml_array.get(h.data, key_index(h, key));
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var k = param.key;
diff --git a/lib/js/map.js b/lib/js/map.js
index a0a5f705f2..17e5215f8a 100644
--- a/lib/js/map.js
+++ b/lib/js/map.js
@@ -5,10 +5,10 @@ var Caml_option = require("./caml_option.js");
 
 function Make(funarg) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, x, d, r) {
@@ -32,26 +32,28 @@ function Make(funarg) {
           };
   };
   var bal = function (l, x, d, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var ld = l.d;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, ld, create(lr, x, d, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var ld = l.d;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, ld, create(lr, x, d, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
@@ -67,23 +69,23 @@ function Make(funarg) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rd = r.d;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, x, d, rl), rv, rd, rr);
-      }
-      if (rl) {
-        return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rd = r.d;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, x, d, rl), rv, rd, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -91,14 +93,14 @@ function Make(funarg) {
         };
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var add = function (x, data, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -143,63 +145,63 @@ function Make(funarg) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var c = Curry._2(funarg.compare, x, param.v);
-        if (c === 0) {
-          return param.d;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = Curry._2(funarg.compare, x, param.v);
+      if (c === 0) {
+        return param.d;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _d0 = param.d;
-          var _param$1 = param.l;
-          while(true) {
-            var param$1 = _param$1;
-            var d0 = _d0;
-            var v0 = _v0;
-            if (!param$1) {
-              return [
-                      v0,
-                      d0
-                    ];
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.l;
-              _d0 = param$1.d;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.r;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _d0 = param.d;
+        var _param$1 = param.l;
+        while(true) {
+          var param$1 = _param$1;
+          var d0 = _d0;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return [
+                    v0,
+                    d0
+                  ];
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.l;
+            _d0 = param$1.d;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.r;
-        continue ;
+          }
+          _param$1 = param$1.r;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -211,7 +213,7 @@ function Make(funarg) {
           var param$1 = _param$1;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return [
                     v0,
                     d0
@@ -235,46 +237,46 @@ function Make(funarg) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _d0 = param.d;
-          var _param$1 = param.r;
-          while(true) {
-            var param$1 = _param$1;
-            var d0 = _d0;
-            var v0 = _v0;
-            if (!param$1) {
-              return [
-                      v0,
-                      d0
-                    ];
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.r;
-              _d0 = param$1.d;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.l;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _d0 = param.d;
+        var _param$1 = param.r;
+        while(true) {
+          var param$1 = _param$1;
+          var d0 = _d0;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return [
+                    v0,
+                    d0
+                  ];
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.r;
+            _d0 = param$1.d;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.l;
-        continue ;
+          }
+          _param$1 = param$1.l;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -286,7 +288,7 @@ function Make(funarg) {
           var param$1 = _param$1;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return [
                     v0,
                     d0
@@ -310,7 +312,7 @@ function Make(funarg) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -324,7 +326,7 @@ function Make(funarg) {
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -338,31 +340,31 @@ function Make(funarg) {
   var min_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return [
                 param.v,
                 param.d
@@ -375,31 +377,31 @@ function Make(funarg) {
   var max_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return [
                 param.v,
                 param.d
@@ -410,32 +412,32 @@ function Make(funarg) {
     };
   };
   var remove_min_binding = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_binding(l), param.v, param.d, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Map.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_binding(l), param.v, param.d, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
     return bal(t1, match[0], match[1], remove_min_binding(t2));
   };
   var remove = function (x, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -462,62 +464,62 @@ function Make(funarg) {
     }
   };
   var update = function (x, f, m) {
-    if (m) {
-      var r = m.r;
-      var d = m.d;
-      var v = m.v;
-      var l = m.l;
-      var c = Curry._2(funarg.compare, x, v);
-      if (c === 0) {
-        var data = Curry._1(f, Caml_option.some(d));
-        if (data === undefined) {
-          return merge(l, r);
-        }
-        var data$1 = Caml_option.valFromOption(data);
-        if (d === data$1) {
-          return m;
-        } else {
-          return /* Node */{
-                  l: l,
-                  v: x,
-                  d: data$1,
-                  r: r,
-                  h: m.h
-                };
-        }
+    if (/* tag */typeof m === "number") {
+      var data = Curry._1(f, undefined);
+      if (data !== undefined) {
+        return /* Node */{
+                l: /* Empty */0,
+                v: x,
+                d: Caml_option.valFromOption(data),
+                r: /* Empty */0,
+                h: 1
+              };
+      } else {
+        return /* Empty */0;
       }
-      if (c < 0) {
-        var ll = update(x, f, l);
-        if (l === ll) {
-          return m;
-        } else {
-          return bal(ll, v, d, r);
-        }
+    }
+    var r = m.r;
+    var d = m.d;
+    var v = m.v;
+    var l = m.l;
+    var c = Curry._2(funarg.compare, x, v);
+    if (c === 0) {
+      var data$1 = Curry._1(f, Caml_option.some(d));
+      if (data$1 === undefined) {
+        return merge(l, r);
+      }
+      var data$2 = Caml_option.valFromOption(data$1);
+      if (d === data$2) {
+        return m;
+      } else {
+        return /* Node */{
+                l: l,
+                v: x,
+                d: data$2,
+                r: r,
+                h: m.h
+              };
       }
-      var rr = update(x, f, r);
-      if (r === rr) {
+    }
+    if (c < 0) {
+      var ll = update(x, f, l);
+      if (l === ll) {
         return m;
       } else {
-        return bal(l, v, d, rr);
+        return bal(ll, v, d, r);
       }
     }
-    var data$2 = Curry._1(f, undefined);
-    if (data$2 !== undefined) {
-      return /* Node */{
-              l: /* Empty */0,
-              v: x,
-              d: Caml_option.valFromOption(data$2),
-              r: /* Empty */0,
-              h: 1
-            };
+    var rr = update(x, f, r);
+    if (r === rr) {
+      return m;
     } else {
-      return /* Empty */0;
+      return bal(l, v, d, rr);
     }
   };
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -527,7 +529,7 @@ function Make(funarg) {
     };
   };
   var map = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var l$p = map(f, param.l);
@@ -542,7 +544,7 @@ function Make(funarg) {
           };
   };
   var mapi = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param.v;
@@ -561,7 +563,7 @@ function Make(funarg) {
     while(true) {
       var accu = _accu;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return accu;
       }
       _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -572,7 +574,7 @@ function Make(funarg) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._2(p, param.v, param.d)) {
@@ -588,7 +590,7 @@ function Make(funarg) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._2(p, param.v, param.d)) {
@@ -602,28 +604,28 @@ function Make(funarg) {
     };
   };
   var add_min_binding = function (k, x, param) {
-    if (param) {
-      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
     }
   };
   var add_max_binding = function (k, x, param) {
-    if (param) {
-      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
     }
   };
   var join = function (l, v, d, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_binding(v, d, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_binding(v, d, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, l.d, join(l.r, v, d, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -633,10 +635,10 @@ function Make(funarg) {
     }
   };
   var concat = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
@@ -650,7 +652,7 @@ function Make(funarg) {
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               undefined,
@@ -685,42 +687,45 @@ function Make(funarg) {
           ];
   };
   var merge$1 = function (f, s1, s2) {
-    if (s1) {
+    if (/* tag */typeof s1 === "number") {
+      if (/* tag */typeof s2 === "number") {
+        return /* Empty */0;
+      }
+      
+    } else {
       var v1 = s1.v;
       if (s1.h >= height(s2)) {
         var match = split(v1, s2);
         return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
       }
       
-    } else if (!s2) {
-      return /* Empty */0;
     }
-    if (s2) {
-      var v2 = s2.v;
-      var match$1 = split(v2, s1);
-      return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+    if (/* tag */typeof s2 === "number") {
+      throw {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "map.ml",
+              393,
+              10
+            ],
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "map.ml",
-            393,
-            10
-          ],
-          Error: new Error()
-        };
+    var v2 = s2.v;
+    var match$1 = split(v2, s1);
+    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   };
   var union = function (f, s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var d1 = s1.d;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var d2 = s2.d;
     var v2 = s2.v;
-    var d1 = s1.d;
-    var v1 = s1.v;
     if (s1.h >= s2.h) {
       var match = split(v1, s2);
       var d2$1 = match[1];
@@ -743,7 +748,7 @@ function Make(funarg) {
     }
   };
   var filter = function (p, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -764,7 +769,7 @@ function Make(funarg) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -795,7 +800,7 @@ function Make(funarg) {
     while(true) {
       var e = _e;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return e;
       }
       _e = /* More */{
@@ -814,14 +819,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -843,14 +848,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return false;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return true;
+        } else {
+          return false;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return false;
       }
       if (Curry._2(funarg.compare, e1._0, e2._0) !== 0) {
@@ -865,17 +870,17 @@ function Make(funarg) {
     };
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var bindings_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
diff --git a/lib/js/mapLabels.js b/lib/js/mapLabels.js
index 164884dcaa..7212153a62 100644
--- a/lib/js/mapLabels.js
+++ b/lib/js/mapLabels.js
@@ -5,10 +5,10 @@ var Caml_option = require("./caml_option.js");
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, x, d, r) {
@@ -32,26 +32,28 @@ function Make(Ord) {
           };
   };
   var bal = function (l, x, d, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var ld = l.d;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, ld, create(lr, x, d, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var ld = l.d;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, ld, create(lr, x, d, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
@@ -67,23 +69,23 @@ function Make(Ord) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rd = r.d;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, x, d, rl), rv, rd, rr);
-      }
-      if (rl) {
-        return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Map.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rd = r.d;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, x, d, rl), rv, rd, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Map.bal",
@@ -91,14 +93,14 @@ function Make(Ord) {
         };
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var add = function (x, data, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -143,18 +145,18 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var c = Curry._2(Ord.compare, x, param.v);
-        if (c === 0) {
-          return param.d;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var c = Curry._2(Ord.compare, x, param.v);
+      if (c === 0) {
+        return param.d;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first_aux = function (_v0, _d0, f, _param) {
@@ -162,7 +164,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -182,18 +184,18 @@ function Make(Ord) {
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_first_aux(v, param.d, f, param.l);
-        }
-        _param = param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_first_aux(v, param.d, f, param.l);
+      }
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt_aux = function (_v0, _d0, f, _param) {
@@ -201,7 +203,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -221,7 +223,7 @@ function Make(Ord) {
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -237,7 +239,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -257,18 +259,18 @@ function Make(Ord) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_last_aux(v, param.d, f, param.r);
-        }
-        _param = param.l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_last_aux(v, param.d, f, param.r);
+      }
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt_aux = function (_v0, _d0, f, _param) {
@@ -276,7 +278,7 @@ function Make(Ord) {
       var param = _param;
       var d0 = _d0;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return [
                 v0,
                 d0
@@ -296,7 +298,7 @@ function Make(Ord) {
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -310,7 +312,7 @@ function Make(Ord) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -324,7 +326,7 @@ function Make(Ord) {
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -338,31 +340,31 @@ function Make(Ord) {
   var min_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return [
                 param.v,
                 param.d
@@ -375,31 +377,31 @@ function Make(Ord) {
   var max_binding = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return [
-                  param.v,
-                  param.d
-                ];
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return [
+                param.v,
+                param.d
+              ];
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_binding_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return [
                 param.v,
                 param.d
@@ -410,32 +412,32 @@ function Make(Ord) {
     };
   };
   var remove_min_binding = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_binding(l), param.v, param.d, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Map.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_binding(l), param.v, param.d, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Map.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
     return bal(t1, match[0], match[1], remove_min_binding(t2));
   };
   var remove = function (x, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -462,62 +464,62 @@ function Make(Ord) {
     }
   };
   var update = function (x, f, m) {
-    if (m) {
-      var r = m.r;
-      var d = m.d;
-      var v = m.v;
-      var l = m.l;
-      var c = Curry._2(Ord.compare, x, v);
-      if (c === 0) {
-        var data = Curry._1(f, Caml_option.some(d));
-        if (data === undefined) {
-          return merge(l, r);
-        }
-        var data$1 = Caml_option.valFromOption(data);
-        if (d === data$1) {
-          return m;
-        } else {
-          return /* Node */{
-                  l: l,
-                  v: x,
-                  d: data$1,
-                  r: r,
-                  h: m.h
-                };
-        }
+    if (/* tag */typeof m === "number") {
+      var data = Curry._1(f, undefined);
+      if (data !== undefined) {
+        return /* Node */{
+                l: /* Empty */0,
+                v: x,
+                d: Caml_option.valFromOption(data),
+                r: /* Empty */0,
+                h: 1
+              };
+      } else {
+        return /* Empty */0;
       }
-      if (c < 0) {
-        var ll = update(x, f, l);
-        if (l === ll) {
-          return m;
-        } else {
-          return bal(ll, v, d, r);
-        }
+    }
+    var r = m.r;
+    var d = m.d;
+    var v = m.v;
+    var l = m.l;
+    var c = Curry._2(Ord.compare, x, v);
+    if (c === 0) {
+      var data$1 = Curry._1(f, Caml_option.some(d));
+      if (data$1 === undefined) {
+        return merge(l, r);
       }
-      var rr = update(x, f, r);
-      if (r === rr) {
+      var data$2 = Caml_option.valFromOption(data$1);
+      if (d === data$2) {
         return m;
       } else {
-        return bal(l, v, d, rr);
+        return /* Node */{
+                l: l,
+                v: x,
+                d: data$2,
+                r: r,
+                h: m.h
+              };
       }
     }
-    var data$2 = Curry._1(f, undefined);
-    if (data$2 !== undefined) {
-      return /* Node */{
-              l: /* Empty */0,
-              v: x,
-              d: Caml_option.valFromOption(data$2),
-              r: /* Empty */0,
-              h: 1
-            };
+    if (c < 0) {
+      var ll = update(x, f, l);
+      if (l === ll) {
+        return m;
+      } else {
+        return bal(ll, v, d, r);
+      }
+    }
+    var rr = update(x, f, r);
+    if (r === rr) {
+      return m;
     } else {
-      return /* Empty */0;
+      return bal(l, v, d, rr);
     }
   };
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -527,7 +529,7 @@ function Make(Ord) {
     };
   };
   var map = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var l$p = map(f, param.l);
@@ -542,7 +544,7 @@ function Make(Ord) {
           };
   };
   var mapi = function (f, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return /* Empty */0;
     }
     var v = param.v;
@@ -561,7 +563,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return accu;
       }
       _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -572,7 +574,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._2(p, param.v, param.d)) {
@@ -588,7 +590,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._2(p, param.v, param.d)) {
@@ -602,28 +604,28 @@ function Make(Ord) {
     };
   };
   var add_min_binding = function (k, x, param) {
-    if (param) {
-      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
     }
   };
   var add_max_binding = function (k, x, param) {
-    if (param) {
-      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(k, x);
+    } else {
+      return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
     }
   };
   var join = function (l, v, d, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_binding(v, d, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_binding(v, d, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, l.d, join(l.r, v, d, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -633,10 +635,10 @@ function Make(Ord) {
     }
   };
   var concat = function (t1, t2) {
-    if (!t1) {
+    if (/* tag */typeof t1 === "number") {
       return t2;
     }
-    if (!t2) {
+    if (/* tag */typeof t2 === "number") {
       return t1;
     }
     var match = min_binding(t2);
@@ -650,7 +652,7 @@ function Make(Ord) {
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               undefined,
@@ -685,42 +687,45 @@ function Make(Ord) {
           ];
   };
   var merge$1 = function (f, s1, s2) {
-    if (s1) {
+    if (/* tag */typeof s1 === "number") {
+      if (/* tag */typeof s2 === "number") {
+        return /* Empty */0;
+      }
+      
+    } else {
       var v1 = s1.v;
       if (s1.h >= height(s2)) {
         var match = split(v1, s2);
         return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
       }
       
-    } else if (!s2) {
-      return /* Empty */0;
     }
-    if (s2) {
-      var v2 = s2.v;
-      var match$1 = split(v2, s1);
-      return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+    if (/* tag */typeof s2 === "number") {
+      throw {
+            RE_EXN_ID: "Assert_failure",
+            _1: [
+              "mapLabels.ml",
+              393,
+              10
+            ],
+            Error: new Error()
+          };
     }
-    throw {
-          RE_EXN_ID: "Assert_failure",
-          _1: [
-            "mapLabels.ml",
-            393,
-            10
-          ],
-          Error: new Error()
-        };
+    var v2 = s2.v;
+    var match$1 = split(v2, s1);
+    return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
   };
   var union = function (f, s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var d1 = s1.d;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var d2 = s2.d;
     var v2 = s2.v;
-    var d1 = s1.d;
-    var v1 = s1.v;
     if (s1.h >= s2.h) {
       var match = split(v1, s2);
       var d2$1 = match[1];
@@ -743,7 +748,7 @@ function Make(Ord) {
     }
   };
   var filter = function (p, m) {
-    if (!m) {
+    if (/* tag */typeof m === "number") {
       return /* Empty */0;
     }
     var r = m.r;
@@ -764,7 +769,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -795,7 +800,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var m = _m;
-      if (!m) {
+      if (/* tag */typeof m === "number") {
         return e;
       }
       _e = /* More */{
@@ -814,14 +819,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -843,14 +848,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return false;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return true;
+        } else {
+          return false;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return false;
       }
       if (Curry._2(Ord.compare, e1._0, e2._0) !== 0) {
@@ -865,17 +870,17 @@ function Make(Ord) {
     };
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var bindings_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
diff --git a/lib/js/moreLabels.js b/lib/js/moreLabels.js
index 364df10b20..03acaedc08 100644
--- a/lib/js/moreLabels.js
+++ b/lib/js/moreLabels.js
@@ -35,10 +35,10 @@ var Hashtbl = {
 var $$Map = {
   Make: (function (funarg) {
       var height = function (param) {
-        if (param) {
-          return param.h;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return param.h;
         }
       };
       var create = function (l, x, d, r) {
@@ -62,26 +62,28 @@ var $$Map = {
               };
       };
       var bal = function (l, x, d, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         if (hl > (hr + 2 | 0)) {
-          if (l) {
-            var lr = l.r;
-            var ld = l.d;
-            var lv = l.v;
-            var ll = l.l;
-            if (height(ll) >= height(lr)) {
-              return create(ll, lv, ld, create(lr, x, d, r));
-            }
-            if (lr) {
-              return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
-            }
+          if (/* tag */typeof l === "number") {
             throw {
                   RE_EXN_ID: "Invalid_argument",
                   _1: "Map.bal",
                   Error: new Error()
                 };
           }
+          var lr = l.r;
+          var ld = l.d;
+          var lv = l.v;
+          var ll = l.l;
+          if (height(ll) >= height(lr)) {
+            return create(ll, lv, ld, create(lr, x, d, r));
+          }
+          if (/* tag */typeof lr !== "number") {
+            return create(create(ll, lv, ld, lr.l), lr.v, lr.d, create(lr.r, x, d, r));
+          }
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Map.bal",
@@ -97,23 +99,23 @@ var $$Map = {
                   h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
                 };
         }
-        if (r) {
-          var rr = r.r;
-          var rd = r.d;
-          var rv = r.v;
-          var rl = r.l;
-          if (height(rr) >= height(rl)) {
-            return create(create(l, x, d, rl), rv, rd, rr);
-          }
-          if (rl) {
-            return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
-          }
+        if (/* tag */typeof r === "number") {
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Map.bal",
                 Error: new Error()
               };
         }
+        var rr = r.r;
+        var rd = r.d;
+        var rv = r.v;
+        var rl = r.l;
+        if (height(rr) >= height(rl)) {
+          return create(create(l, x, d, rl), rv, rd, rr);
+        }
+        if (/* tag */typeof rl !== "number") {
+          return create(create(l, x, d, rl.l), rl.v, rl.d, create(rl.r, rv, rd, rr));
+        }
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Map.bal",
@@ -121,14 +123,14 @@ var $$Map = {
             };
       };
       var is_empty = function (param) {
-        if (param) {
-          return false;
-        } else {
+        if (/* tag */typeof param === "number") {
           return true;
+        } else {
+          return false;
         }
       };
       var add = function (x, data, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Node */{
                   l: /* Empty */0,
                   v: x,
@@ -173,18 +175,18 @@ var $$Map = {
       var find = function (x, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var c = Curry._2(funarg.compare, x, param.v);
-            if (c === 0) {
-              return param.d;
-            }
-            _param = c < 0 ? param.l : param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var c = Curry._2(funarg.compare, x, param.v);
+          if (c === 0) {
+            return param.d;
+          }
+          _param = c < 0 ? param.l : param.r;
+          continue ;
         };
       };
       var find_first_aux = function (_v0, _d0, f, _param) {
@@ -192,7 +194,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -212,18 +214,18 @@ var $$Map = {
       var find_first = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_first_aux(v, param.d, f, param.l);
-            }
-            _param = param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_first_aux(v, param.d, f, param.l);
+          }
+          _param = param.r;
+          continue ;
         };
       };
       var find_first_opt_aux = function (_v0, _d0, f, _param) {
@@ -231,7 +233,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -251,7 +253,7 @@ var $$Map = {
       var find_first_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -267,7 +269,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -287,18 +289,18 @@ var $$Map = {
       var find_last = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_last_aux(v, param.d, f, param.r);
-            }
-            _param = param.l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_last_aux(v, param.d, f, param.r);
+          }
+          _param = param.l;
+          continue ;
         };
       };
       var find_last_opt_aux = function (_v0, _d0, f, _param) {
@@ -306,7 +308,7 @@ var $$Map = {
           var param = _param;
           var d0 = _d0;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return [
                     v0,
                     d0
@@ -326,7 +328,7 @@ var $$Map = {
       var find_last_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -340,7 +342,7 @@ var $$Map = {
       var find_opt = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -354,7 +356,7 @@ var $$Map = {
       var mem = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -368,31 +370,31 @@ var $$Map = {
       var min_binding = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var l = param.l;
-            if (!l) {
-              return [
-                      param.v,
-                      param.d
-                    ];
-            }
-            _param = l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var l = param.l;
+          if (/* tag */typeof l === "number") {
+            return [
+                    param.v,
+                    param.d
+                  ];
+          }
+          _param = l;
+          continue ;
         };
       };
       var min_binding_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var l = param.l;
-          if (!l) {
+          if (/* tag */typeof l === "number") {
             return [
                     param.v,
                     param.d
@@ -405,31 +407,31 @@ var $$Map = {
       var max_binding = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var r = param.r;
-            if (!r) {
-              return [
-                      param.v,
-                      param.d
-                    ];
-            }
-            _param = r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var r = param.r;
+          if (/* tag */typeof r === "number") {
+            return [
+                    param.v,
+                    param.d
+                  ];
+          }
+          _param = r;
+          continue ;
         };
       };
       var max_binding_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var r = param.r;
-          if (!r) {
+          if (/* tag */typeof r === "number") {
             return [
                     param.v,
                     param.d
@@ -440,32 +442,32 @@ var $$Map = {
         };
       };
       var remove_min_binding = function (param) {
-        if (param) {
-          var l = param.l;
-          if (l) {
-            return bal(remove_min_binding(l), param.v, param.d, param.r);
-          } else {
-            return param.r;
-          }
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Invalid_argument",
+                _1: "Map.remove_min_elt",
+                Error: new Error()
+              };
+        }
+        var l = param.l;
+        if (/* tag */typeof l === "number") {
+          return param.r;
+        } else {
+          return bal(remove_min_binding(l), param.v, param.d, param.r);
         }
-        throw {
-              RE_EXN_ID: "Invalid_argument",
-              _1: "Map.remove_min_elt",
-              Error: new Error()
-            };
       };
       var merge = function (t1, t2) {
-        if (!t1) {
+        if (/* tag */typeof t1 === "number") {
           return t2;
         }
-        if (!t2) {
+        if (/* tag */typeof t2 === "number") {
           return t1;
         }
         var match = min_binding(t2);
         return bal(t1, match[0], match[1], remove_min_binding(t2));
       };
       var remove = function (x, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Empty */0;
         }
         var r = m.r;
@@ -492,62 +494,62 @@ var $$Map = {
         }
       };
       var update = function (x, f, m) {
-        if (m) {
-          var r = m.r;
-          var d = m.d;
-          var v = m.v;
-          var l = m.l;
-          var c = Curry._2(funarg.compare, x, v);
-          if (c === 0) {
-            var data = Curry._1(f, Caml_option.some(d));
-            if (data === undefined) {
-              return merge(l, r);
-            }
-            var data$1 = Caml_option.valFromOption(data);
-            if (d === data$1) {
-              return m;
-            } else {
-              return /* Node */{
-                      l: l,
-                      v: x,
-                      d: data$1,
-                      r: r,
-                      h: m.h
-                    };
-            }
+        if (/* tag */typeof m === "number") {
+          var data = Curry._1(f, undefined);
+          if (data !== undefined) {
+            return /* Node */{
+                    l: /* Empty */0,
+                    v: x,
+                    d: Caml_option.valFromOption(data),
+                    r: /* Empty */0,
+                    h: 1
+                  };
+          } else {
+            return /* Empty */0;
           }
-          if (c < 0) {
-            var ll = update(x, f, l);
-            if (l === ll) {
-              return m;
-            } else {
-              return bal(ll, v, d, r);
-            }
+        }
+        var r = m.r;
+        var d = m.d;
+        var v = m.v;
+        var l = m.l;
+        var c = Curry._2(funarg.compare, x, v);
+        if (c === 0) {
+          var data$1 = Curry._1(f, Caml_option.some(d));
+          if (data$1 === undefined) {
+            return merge(l, r);
           }
-          var rr = update(x, f, r);
-          if (r === rr) {
+          var data$2 = Caml_option.valFromOption(data$1);
+          if (d === data$2) {
             return m;
           } else {
-            return bal(l, v, d, rr);
+            return /* Node */{
+                    l: l,
+                    v: x,
+                    d: data$2,
+                    r: r,
+                    h: m.h
+                  };
           }
         }
-        var data$2 = Curry._1(f, undefined);
-        if (data$2 !== undefined) {
-          return /* Node */{
-                  l: /* Empty */0,
-                  v: x,
-                  d: Caml_option.valFromOption(data$2),
-                  r: /* Empty */0,
-                  h: 1
-                };
+        if (c < 0) {
+          var ll = update(x, f, l);
+          if (l === ll) {
+            return m;
+          } else {
+            return bal(ll, v, d, r);
+          }
+        }
+        var rr = update(x, f, r);
+        if (r === rr) {
+          return m;
         } else {
-          return /* Empty */0;
+          return bal(l, v, d, rr);
         }
       };
       var iter = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           iter(f, param.l);
@@ -557,7 +559,7 @@ var $$Map = {
         };
       };
       var map = function (f, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* Empty */0;
         }
         var l$p = map(f, param.l);
@@ -572,7 +574,7 @@ var $$Map = {
               };
       };
       var mapi = function (f, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return /* Empty */0;
         }
         var v = param.v;
@@ -591,7 +593,7 @@ var $$Map = {
         while(true) {
           var accu = _accu;
           var m = _m;
-          if (!m) {
+          if (/* tag */typeof m === "number") {
             return accu;
           }
           _accu = Curry._3(f, m.v, m.d, fold(f, m.l, accu));
@@ -602,7 +604,7 @@ var $$Map = {
       var for_all = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return true;
           }
           if (!Curry._2(p, param.v, param.d)) {
@@ -618,7 +620,7 @@ var $$Map = {
       var exists = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           if (Curry._2(p, param.v, param.d)) {
@@ -632,28 +634,28 @@ var $$Map = {
         };
       };
       var add_min_binding = function (k, x, param) {
-        if (param) {
-          return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(k, x);
+        } else {
+          return bal(add_min_binding(k, x, param.l), param.v, param.d, param.r);
         }
       };
       var add_max_binding = function (k, x, param) {
-        if (param) {
-          return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(k, x);
+        } else {
+          return bal(param.l, param.v, param.d, add_max_binding(k, x, param.r));
         }
       };
       var join = function (l, v, d, r) {
-        if (!l) {
+        if (/* tag */typeof l === "number") {
           return add_min_binding(v, d, r);
         }
-        if (!r) {
+        var lh = l.h;
+        if (/* tag */typeof r === "number") {
           return add_max_binding(v, d, l);
         }
         var rh = r.h;
-        var lh = l.h;
         if (lh > (rh + 2 | 0)) {
           return bal(l.l, l.v, l.d, join(l.r, v, d, r));
         } else if (rh > (lh + 2 | 0)) {
@@ -663,10 +665,10 @@ var $$Map = {
         }
       };
       var concat = function (t1, t2) {
-        if (!t1) {
+        if (/* tag */typeof t1 === "number") {
           return t2;
         }
-        if (!t2) {
+        if (/* tag */typeof t2 === "number") {
           return t1;
         }
         var match = min_binding(t2);
@@ -680,7 +682,7 @@ var $$Map = {
         }
       };
       var split = function (x, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   undefined,
@@ -715,42 +717,45 @@ var $$Map = {
               ];
       };
       var merge$1 = function (f, s1, s2) {
-        if (s1) {
+        if (/* tag */typeof s1 === "number") {
+          if (/* tag */typeof s2 === "number") {
+            return /* Empty */0;
+          }
+          
+        } else {
           var v1 = s1.v;
           if (s1.h >= height(s2)) {
             var match = split(v1, s2);
             return concat_or_join(merge$1(f, s1.l, match[0]), v1, Curry._3(f, v1, Caml_option.some(s1.d), match[1]), merge$1(f, s1.r, match[2]));
           }
           
-        } else if (!s2) {
-          return /* Empty */0;
         }
-        if (s2) {
-          var v2 = s2.v;
-          var match$1 = split(v2, s1);
-          return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
+        if (/* tag */typeof s2 === "number") {
+          throw {
+                RE_EXN_ID: "Assert_failure",
+                _1: [
+                  "mapLabels.ml",
+                  393,
+                  10
+                ],
+                Error: new Error()
+              };
         }
-        throw {
-              RE_EXN_ID: "Assert_failure",
-              _1: [
-                "mapLabels.ml",
-                393,
-                10
-              ],
-              Error: new Error()
-            };
+        var v2 = s2.v;
+        var match$1 = split(v2, s1);
+        return concat_or_join(merge$1(f, match$1[0], s2.l), v2, Curry._3(f, v2, match$1[1], Caml_option.some(s2.d)), merge$1(f, match$1[2], s2.r));
       };
       var union = function (f, s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return s2;
         }
-        if (!s2) {
+        var d1 = s1.d;
+        var v1 = s1.v;
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var d2 = s2.d;
         var v2 = s2.v;
-        var d1 = s1.d;
-        var v1 = s1.v;
         if (s1.h >= s2.h) {
           var match = split(v1, s2);
           var d2$1 = match[1];
@@ -773,7 +778,7 @@ var $$Map = {
         }
       };
       var filter = function (p, m) {
-        if (!m) {
+        if (/* tag */typeof m === "number") {
           return /* Empty */0;
         }
         var r = m.r;
@@ -794,7 +799,7 @@ var $$Map = {
         }
       };
       var partition = function (p, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   /* Empty */0
@@ -825,7 +830,7 @@ var $$Map = {
         while(true) {
           var e = _e;
           var m = _m;
-          if (!m) {
+          if (/* tag */typeof m === "number") {
             return e;
           }
           _e = /* More */{
@@ -844,14 +849,14 @@ var $$Map = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return -1;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return 0;
+            } else {
+              return -1;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return 1;
           }
           var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -873,14 +878,14 @@ var $$Map = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return false;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return true;
+            } else {
+              return false;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return false;
           }
           if (Curry._2(funarg.compare, e1._0, e2._0) !== 0) {
@@ -895,17 +900,17 @@ var $$Map = {
         };
       };
       var cardinal = function (param) {
-        if (param) {
-          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
         }
       };
       var bindings_aux = function (_accu, _param) {
         while(true) {
           var param = _param;
           var accu = _accu;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return accu;
           }
           _param = param.l;
@@ -964,15 +969,17 @@ var $$Map = {
 var $$Set = {
   Make: (function (funarg) {
       var height = function (param) {
-        if (param) {
-          return param.h;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return param.h;
         }
       };
       var create = function (l, v, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         return /* Node */{
                 l: l,
                 v: v,
@@ -981,25 +988,27 @@ var $$Set = {
               };
       };
       var bal = function (l, v, r) {
-        var hl = l ? l.h : 0;
-        var hr = r ? r.h : 0;
+        var hl;
+        hl = /* tag */typeof l === "number" ? 0 : l.h;
+        var hr;
+        hr = /* tag */typeof r === "number" ? 0 : r.h;
         if (hl > (hr + 2 | 0)) {
-          if (l) {
-            var lr = l.r;
-            var lv = l.v;
-            var ll = l.l;
-            if (height(ll) >= height(lr)) {
-              return create(ll, lv, create(lr, v, r));
-            }
-            if (lr) {
-              return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-            }
+          if (/* tag */typeof l === "number") {
             throw {
                   RE_EXN_ID: "Invalid_argument",
                   _1: "Set.bal",
                   Error: new Error()
                 };
           }
+          var lr = l.r;
+          var lv = l.v;
+          var ll = l.l;
+          if (height(ll) >= height(lr)) {
+            return create(ll, lv, create(lr, v, r));
+          }
+          if (/* tag */typeof lr !== "number") {
+            return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+          }
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Set.bal",
@@ -1014,22 +1023,22 @@ var $$Set = {
                   h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
                 };
         }
-        if (r) {
-          var rr = r.r;
-          var rv = r.v;
-          var rl = r.l;
-          if (height(rr) >= height(rl)) {
-            return create(create(l, v, rl), rv, rr);
-          }
-          if (rl) {
-            return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-          }
+        if (/* tag */typeof r === "number") {
           throw {
                 RE_EXN_ID: "Invalid_argument",
                 _1: "Set.bal",
                 Error: new Error()
               };
         }
+        var rr = r.r;
+        var rv = r.v;
+        var rl = r.l;
+        if (height(rr) >= height(rl)) {
+          return create(create(l, v, rl), rv, rr);
+        }
+        if (/* tag */typeof rl !== "number") {
+          return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+        }
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
@@ -1037,7 +1046,7 @@ var $$Set = {
             };
       };
       var add = function (x, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Node */{
                   l: /* Empty */0,
                   v: x,
@@ -1076,28 +1085,28 @@ var $$Set = {
               };
       };
       var add_min_element = function (x, param) {
-        if (param) {
-          return bal(add_min_element(x, param.l), param.v, param.r);
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(x);
+        } else {
+          return bal(add_min_element(x, param.l), param.v, param.r);
         }
       };
       var add_max_element = function (x, param) {
-        if (param) {
-          return bal(param.l, param.v, add_max_element(x, param.r));
-        } else {
+        if (/* tag */typeof param === "number") {
           return singleton(x);
+        } else {
+          return bal(param.l, param.v, add_max_element(x, param.r));
         }
       };
       var join = function (l, v, r) {
-        if (!l) {
+        if (/* tag */typeof l === "number") {
           return add_min_element(v, r);
         }
-        if (!r) {
+        var lh = l.h;
+        if (/* tag */typeof r === "number") {
           return add_max_element(v, l);
         }
         var rh = r.h;
-        var lh = l.h;
         if (lh > (rh + 2 | 0)) {
           return bal(l.l, l.v, join(l.r, v, r));
         } else if (rh > (lh + 2 | 0)) {
@@ -1109,28 +1118,28 @@ var $$Set = {
       var min_elt = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var l = param.l;
-            if (!l) {
-              return param.v;
-            }
-            _param = l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var l = param.l;
+          if (/* tag */typeof l === "number") {
+            return param.v;
+          }
+          _param = l;
+          continue ;
         };
       };
       var min_elt_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var l = param.l;
-          if (!l) {
+          if (/* tag */typeof l === "number") {
             return Caml_option.some(param.v);
           }
           _param = l;
@@ -1140,28 +1149,28 @@ var $$Set = {
       var max_elt = function (_param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var r = param.r;
-            if (!r) {
-              return param.v;
-            }
-            _param = r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var r = param.r;
+          if (/* tag */typeof r === "number") {
+            return param.v;
+          }
+          _param = r;
+          continue ;
         };
       };
       var max_elt_opt = function (_param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var r = param.r;
-          if (!r) {
+          if (/* tag */typeof r === "number") {
             return Caml_option.some(param.v);
           }
           _param = r;
@@ -1169,44 +1178,40 @@ var $$Set = {
         };
       };
       var remove_min_elt = function (param) {
-        if (param) {
-          var l = param.l;
-          if (l) {
-            return bal(remove_min_elt(l), param.v, param.r);
-          } else {
-            return param.r;
-          }
+        if (/* tag */typeof param === "number") {
+          throw {
+                RE_EXN_ID: "Invalid_argument",
+                _1: "Set.remove_min_elt",
+                Error: new Error()
+              };
+        }
+        var l = param.l;
+        if (/* tag */typeof l === "number") {
+          return param.r;
+        } else {
+          return bal(remove_min_elt(l), param.v, param.r);
         }
-        throw {
-              RE_EXN_ID: "Invalid_argument",
-              _1: "Set.remove_min_elt",
-              Error: new Error()
-            };
       };
       var merge = function (t1, t2) {
-        if (t1) {
-          if (t2) {
-            return bal(t1, min_elt(t2), remove_min_elt(t2));
-          } else {
-            return t1;
-          }
-        } else {
+        if (/* tag */typeof t1 === "number") {
           return t2;
+        } else if (/* tag */typeof t2 === "number") {
+          return t1;
+        } else {
+          return bal(t1, min_elt(t2), remove_min_elt(t2));
         }
       };
       var concat = function (t1, t2) {
-        if (t1) {
-          if (t2) {
-            return join(t1, min_elt(t2), remove_min_elt(t2));
-          } else {
-            return t1;
-          }
-        } else {
+        if (/* tag */typeof t1 === "number") {
           return t2;
+        } else if (/* tag */typeof t2 === "number") {
+          return t1;
+        } else {
+          return join(t1, min_elt(t2), remove_min_elt(t2));
         }
       };
       var split = function (x, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   false,
@@ -1240,16 +1245,16 @@ var $$Set = {
               ];
       };
       var is_empty = function (param) {
-        if (param) {
-          return false;
-        } else {
+        if (/* tag */typeof param === "number") {
           return true;
+        } else {
+          return false;
         }
       };
       var mem = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           var c = Curry._2(funarg.compare, x, param.v);
@@ -1261,7 +1266,7 @@ var $$Set = {
         };
       };
       var remove = function (x, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
@@ -1287,16 +1292,16 @@ var $$Set = {
         }
       };
       var union = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return s2;
         }
-        if (!s2) {
+        var h1 = s1.h;
+        var v1 = s1.v;
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var h2 = s2.h;
         var v2 = s2.v;
-        var h1 = s1.h;
-        var v1 = s1.v;
         if (h1 >= h2) {
           if (h2 === 1) {
             return add(v2, s1);
@@ -1311,10 +1316,10 @@ var $$Set = {
         return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
       };
       var inter = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return /* Empty */0;
         }
-        if (!s2) {
+        if (/* tag */typeof s2 === "number") {
           return /* Empty */0;
         }
         var r1 = s1.r;
@@ -1329,10 +1334,10 @@ var $$Set = {
         }
       };
       var diff = function (s1, s2) {
-        if (!s1) {
+        if (/* tag */typeof s1 === "number") {
           return /* Empty */0;
         }
-        if (!s2) {
+        if (/* tag */typeof s2 === "number") {
           return s1;
         }
         var r1 = s1.r;
@@ -1350,7 +1355,7 @@ var $$Set = {
         while(true) {
           var e = _e;
           var s = _s;
-          if (!s) {
+          if (/* tag */typeof s === "number") {
             return e;
           }
           _e = /* More */{
@@ -1366,14 +1371,14 @@ var $$Set = {
         while(true) {
           var e2 = _e2;
           var e1 = _e1;
-          if (!e1) {
-            if (e2) {
-              return -1;
-            } else {
+          if (/* tag */typeof e1 === "number") {
+            if (/* tag */typeof e2 === "number") {
               return 0;
+            } else {
+              return -1;
             }
           }
-          if (!e2) {
+          if (/* tag */typeof e2 === "number") {
             return 1;
           }
           var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -1395,17 +1400,17 @@ var $$Set = {
         while(true) {
           var s2 = _s2;
           var s1 = _s1;
-          if (!s1) {
+          if (/* tag */typeof s1 === "number") {
             return true;
           }
-          if (!s2) {
+          var r1 = s1.r;
+          var v1 = s1.v;
+          var l1 = s1.l;
+          if (/* tag */typeof s2 === "number") {
             return false;
           }
           var r2 = s2.r;
           var l2 = s2.l;
-          var r1 = s1.r;
-          var v1 = s1.v;
-          var l1 = s1.l;
           var c = Curry._2(funarg.compare, v1, s2.v);
           if (c === 0) {
             if (!subset(l1, l2)) {
@@ -1442,7 +1447,7 @@ var $$Set = {
       var iter = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           iter(f, param.l);
@@ -1455,7 +1460,7 @@ var $$Set = {
         while(true) {
           var accu = _accu;
           var s = _s;
-          if (!s) {
+          if (/* tag */typeof s === "number") {
             return accu;
           }
           _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -1466,7 +1471,7 @@ var $$Set = {
       var for_all = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return true;
           }
           if (!Curry._1(p, param.v)) {
@@ -1482,7 +1487,7 @@ var $$Set = {
       var exists = function (p, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return false;
           }
           if (Curry._1(p, param.v)) {
@@ -1496,7 +1501,7 @@ var $$Set = {
         };
       };
       var filter = function (p, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
@@ -1516,7 +1521,7 @@ var $$Set = {
         }
       };
       var partition = function (p, param) {
-        if (!param) {
+        if (/* tag */typeof param === "number") {
           return [
                   /* Empty */0,
                   /* Empty */0
@@ -1543,17 +1548,17 @@ var $$Set = {
         }
       };
       var cardinal = function (param) {
-        if (param) {
-          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-        } else {
+        if (/* tag */typeof param === "number") {
           return 0;
+        } else {
+          return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
         }
       };
       var elements_aux = function (_accu, _param) {
         while(true) {
           var param = _param;
           var accu = _accu;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return accu;
           }
           _param = param.l;
@@ -1570,26 +1575,26 @@ var $$Set = {
       var find = function (x, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            var c = Curry._2(funarg.compare, x, v);
-            if (c === 0) {
-              return v;
-            }
-            _param = c < 0 ? param.l : param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          var c = Curry._2(funarg.compare, x, v);
+          if (c === 0) {
+            return v;
+          }
+          _param = c < 0 ? param.l : param.r;
+          continue ;
         };
       };
       var find_first_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return v0;
           }
           var v = param.v;
@@ -1605,25 +1610,25 @@ var $$Set = {
       var find_first = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_first_aux(v, f, param.l);
-            }
-            _param = param.r;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_first_aux(v, f, param.l);
+          }
+          _param = param.r;
+          continue ;
         };
       };
       var find_first_opt_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return Caml_option.some(v0);
           }
           var v = param.v;
@@ -1639,7 +1644,7 @@ var $$Set = {
       var find_first_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1654,7 +1659,7 @@ var $$Set = {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return v0;
           }
           var v = param.v;
@@ -1670,25 +1675,25 @@ var $$Set = {
       var find_last = function (f, _param) {
         while(true) {
           var param = _param;
-          if (param) {
-            var v = param.v;
-            if (Curry._1(f, v)) {
-              return find_last_aux(v, f, param.r);
-            }
-            _param = param.l;
-            continue ;
+          if (/* tag */typeof param === "number") {
+            throw {
+                  RE_EXN_ID: "Not_found",
+                  Error: new Error()
+                };
           }
-          throw {
-                RE_EXN_ID: "Not_found",
-                Error: new Error()
-              };
+          var v = param.v;
+          if (Curry._1(f, v)) {
+            return find_last_aux(v, f, param.r);
+          }
+          _param = param.l;
+          continue ;
         };
       };
       var find_last_opt_aux = function (_v0, f, _param) {
         while(true) {
           var param = _param;
           var v0 = _v0;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return Caml_option.some(v0);
           }
           var v = param.v;
@@ -1704,7 +1709,7 @@ var $$Set = {
       var find_last_opt = function (f, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1718,7 +1723,7 @@ var $$Set = {
       var find_opt = function (x, _param) {
         while(true) {
           var param = _param;
-          if (!param) {
+          if (/* tag */typeof param === "number") {
             return ;
           }
           var v = param.v;
@@ -1738,7 +1743,7 @@ var $$Set = {
         }
       };
       var map = function (f, t) {
-        if (!t) {
+        if (/* tag */typeof t === "number") {
           return /* Empty */0;
         }
         var r = t.r;
diff --git a/lib/js/queue.js b/lib/js/queue.js
index 2e7ec96f00..3e1e32c0e1 100644
--- a/lib/js/queue.js
+++ b/lib/js/queue.js
@@ -25,20 +25,20 @@ function add(x, q) {
     next: /* Nil */0
   };
   var last = q.last;
-  if (last) {
-    q.length = q.length + 1 | 0;
-    last.next = cell;
-    q.last = cell;
-  } else {
+  if (/* tag */typeof last === "number") {
     q.length = 1;
     q.first = cell;
     q.last = cell;
+    return ;
   }
+  q.length = q.length + 1 | 0;
+  last.next = cell;
+  q.last = cell;
 }
 
 function peek(q) {
   var match = q.first;
-  if (match) {
+  if (/* tag */typeof match !== "number") {
     return match.content;
   }
   throw {
@@ -49,22 +49,21 @@ function peek(q) {
 
 function take(q) {
   var match = q.first;
-  if (match) {
-    var content = match.content;
-    var next = match.next;
-    if (next) {
-      q.length = q.length - 1 | 0;
-      q.first = next;
-      return content;
-    } else {
-      clear(q);
-      return content;
-    }
+  if (/* tag */typeof match === "number") {
+    throw {
+          RE_EXN_ID: Empty,
+          Error: new Error()
+        };
   }
-  throw {
-        RE_EXN_ID: Empty,
-        Error: new Error()
-      };
+  var content = match.content;
+  var next = match.next;
+  if (/* tag */typeof next === "number") {
+    clear(q);
+    return content;
+  }
+  q.length = q.length - 1 | 0;
+  q.first = next;
+  return content;
 }
 
 function copy(q) {
@@ -78,23 +77,23 @@ function copy(q) {
   while(true) {
     var cell = _cell;
     var prev = _prev;
-    if (cell) {
-      var next = cell.next;
-      var res = /* Cons */{
-        content: cell.content,
-        next: /* Nil */0
-      };
-      if (prev) {
-        prev.next = res;
-      } else {
-        q_res.first = res;
-      }
-      _cell = next;
-      _prev = res;
-      continue ;
+    if (/* tag */typeof cell === "number") {
+      q_res.last = prev;
+      return q_res;
+    }
+    var next = cell.next;
+    var res = /* Cons */{
+      content: cell.content,
+      next: /* Nil */0
+    };
+    if (/* tag */typeof prev === "number") {
+      q_res.first = res;
+    } else {
+      prev.next = res;
     }
-    q_res.last = prev;
-    return q_res;
+    _cell = next;
+    _prev = res;
+    continue ;
   };
 }
 
@@ -110,7 +109,7 @@ function iter(f, q) {
   var _cell = q.first;
   while(true) {
     var cell = _cell;
-    if (!cell) {
+    if (/* tag */typeof cell === "number") {
       return ;
     }
     var next = cell.next;
@@ -126,7 +125,7 @@ function fold(f, accu, q) {
   while(true) {
     var cell = _cell;
     var accu$1 = _accu;
-    if (!cell) {
+    if (/* tag */typeof cell === "number") {
       return accu$1;
     }
     var next = cell.next;
@@ -142,17 +141,16 @@ function transfer(q1, q2) {
     return ;
   }
   var last = q2.last;
-  if (last) {
-    q2.length = q2.length + q1.length | 0;
-    last.next = q1.first;
-    q2.last = q1.last;
-    return clear(q1);
-  } else {
+  if (/* tag */typeof last === "number") {
     q2.length = q1.length;
     q2.first = q1.first;
     q2.last = q1.last;
     return clear(q1);
   }
+  q2.length = q2.length + q1.length | 0;
+  last.next = q1.first;
+  q2.last = q1.last;
+  clear(q1);
 }
 
 var push = add;
diff --git a/lib/js/set.js b/lib/js/set.js
index b52ab620bd..b2be2ce778 100644
--- a/lib/js/set.js
+++ b/lib/js/set.js
@@ -6,15 +6,17 @@ var Caml_option = require("./caml_option.js");
 
 function Make(funarg) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     return /* Node */{
             l: l,
             v: v,
@@ -23,25 +25,27 @@ function Make(funarg) {
           };
   };
   var bal = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, create(lr, v, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, create(lr, v, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
@@ -56,22 +60,22 @@ function Make(funarg) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, v, rl), rv, rr);
-      }
-      if (rl) {
-        return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, v, rl), rv, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -79,7 +83,7 @@ function Make(funarg) {
         };
   };
   var add = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -118,28 +122,28 @@ function Make(funarg) {
           };
   };
   var add_min_element = function (x, param) {
-    if (param) {
-      return bal(add_min_element(x, param.l), param.v, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(add_min_element(x, param.l), param.v, param.r);
     }
   };
   var add_max_element = function (x, param) {
-    if (param) {
-      return bal(param.l, param.v, add_max_element(x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(param.l, param.v, add_max_element(x, param.r));
     }
   };
   var join = function (l, v, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_element(v, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_element(v, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, join(l.r, v, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -151,28 +155,28 @@ function Make(funarg) {
   var min_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return param.v;
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return param.v;
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return Caml_option.some(param.v);
       }
       _param = l;
@@ -182,28 +186,28 @@ function Make(funarg) {
   var max_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return param.v;
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return param.v;
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return Caml_option.some(param.v);
       }
       _param = r;
@@ -211,33 +215,31 @@ function Make(funarg) {
     };
   };
   var remove_min_elt = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_elt(l), param.v, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Set.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_elt(l), param.v, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
   };
   var concat = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return join(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return join(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               false,
@@ -271,16 +273,16 @@ function Make(funarg) {
           ];
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(funarg.compare, x, param.v);
@@ -292,7 +294,7 @@ function Make(funarg) {
     };
   };
   var remove = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -300,14 +302,12 @@ function Make(funarg) {
     var l = t.l;
     var c = Curry._2(funarg.compare, x, v);
     if (c === 0) {
-      if (l) {
-        if (r) {
-          return bal(l, min_elt(r), remove_min_elt(r));
-        } else {
-          return l;
-        }
-      } else {
+      if (/* tag */typeof l === "number") {
         return r;
+      } else if (/* tag */typeof r === "number") {
+        return l;
+      } else {
+        return bal(l, min_elt(r), remove_min_elt(r));
       }
     }
     if (c < 0) {
@@ -326,16 +326,16 @@ function Make(funarg) {
     }
   };
   var union = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var h1 = s1.h;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var h2 = s2.h;
     var v2 = s2.v;
-    var h1 = s1.h;
-    var v1 = s1.v;
     if (h1 >= h2) {
       if (h2 === 1) {
         return add(v2, s1);
@@ -350,10 +350,10 @@ function Make(funarg) {
     return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
   };
   var inter = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return /* Empty */0;
     }
     var r1 = s1.r;
@@ -368,10 +368,10 @@ function Make(funarg) {
     }
   };
   var diff = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var r1 = s1.r;
@@ -389,7 +389,7 @@ function Make(funarg) {
     while(true) {
       var e = _e;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return e;
       }
       _e = /* More */{
@@ -407,14 +407,14 @@ function Make(funarg) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(funarg.compare, e1._0, e2._0);
@@ -433,17 +433,17 @@ function Make(funarg) {
     while(true) {
       var s2 = _s2;
       var s1 = _s1;
-      if (!s1) {
+      if (/* tag */typeof s1 === "number") {
         return true;
       }
-      if (!s2) {
+      var r1 = s1.r;
+      var v1 = s1.v;
+      var l1 = s1.l;
+      if (/* tag */typeof s2 === "number") {
         return false;
       }
       var r2 = s2.r;
       var l2 = s2.l;
-      var r1 = s1.r;
-      var v1 = s1.v;
-      var l1 = s1.l;
       var c = Curry._2(funarg.compare, v1, s2.v);
       if (c === 0) {
         if (!subset(l1, l2)) {
@@ -480,7 +480,7 @@ function Make(funarg) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -493,7 +493,7 @@ function Make(funarg) {
     while(true) {
       var accu = _accu;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return accu;
       }
       _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -504,7 +504,7 @@ function Make(funarg) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._1(p, param.v)) {
@@ -520,7 +520,7 @@ function Make(funarg) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._1(p, param.v)) {
@@ -534,7 +534,7 @@ function Make(funarg) {
     };
   };
   var filter = function (p, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -554,7 +554,7 @@ function Make(funarg) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -581,17 +581,17 @@ function Make(funarg) {
     }
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var elements_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
@@ -608,58 +608,58 @@ function Make(funarg) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        var c = Curry._2(funarg.compare, x, v);
-        if (c === 0) {
-          return v;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      var c = Curry._2(funarg.compare, x, v);
+      if (c === 0) {
+        return v;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _param$1 = param.l;
-          while(true) {
-            var param$1 = _param$1;
-            var v0 = _v0;
-            if (!param$1) {
-              return v0;
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.l;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.r;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _param$1 = param.l;
+        while(true) {
+          var param$1 = _param$1;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return v0;
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.l;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.r;
-        continue ;
+          }
+          _param$1 = param$1.r;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -669,7 +669,7 @@ function Make(funarg) {
         while(true) {
           var param$1 = _param$1;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return Caml_option.some(v0);
           }
           var v$1 = param$1.v;
@@ -689,40 +689,40 @@ function Make(funarg) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          var _v0 = v;
-          var _param$1 = param.r;
-          while(true) {
-            var param$1 = _param$1;
-            var v0 = _v0;
-            if (!param$1) {
-              return v0;
-            }
-            var v$1 = param$1.v;
-            if (Curry._1(f, v$1)) {
-              _param$1 = param$1.r;
-              _v0 = v$1;
-              continue ;
-            }
-            _param$1 = param$1.l;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
+      }
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        var _v0 = v;
+        var _param$1 = param.r;
+        while(true) {
+          var param$1 = _param$1;
+          var v0 = _v0;
+          if (/* tag */typeof param$1 === "number") {
+            return v0;
+          }
+          var v$1 = param$1.v;
+          if (Curry._1(f, v$1)) {
+            _param$1 = param$1.r;
+            _v0 = v$1;
             continue ;
-          };
-        }
-        _param = param.l;
-        continue ;
+          }
+          _param$1 = param$1.l;
+          continue ;
+        };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -732,7 +732,7 @@ function Make(funarg) {
         while(true) {
           var param$1 = _param$1;
           var v0 = _v0;
-          if (!param$1) {
+          if (/* tag */typeof param$1 === "number") {
             return Caml_option.some(v0);
           }
           var v$1 = param$1.v;
@@ -752,7 +752,7 @@ function Make(funarg) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -765,7 +765,7 @@ function Make(funarg) {
     };
   };
   var map = function (f, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
diff --git a/lib/js/setLabels.js b/lib/js/setLabels.js
index 8688ef3c3f..9c51e792dd 100644
--- a/lib/js/setLabels.js
+++ b/lib/js/setLabels.js
@@ -6,15 +6,17 @@ var Caml_option = require("./caml_option.js");
 
 function Make(Ord) {
   var height = function (param) {
-    if (param) {
-      return param.h;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return param.h;
     }
   };
   var create = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     return /* Node */{
             l: l,
             v: v,
@@ -23,25 +25,27 @@ function Make(Ord) {
           };
   };
   var bal = function (l, v, r) {
-    var hl = l ? l.h : 0;
-    var hr = r ? r.h : 0;
+    var hl;
+    hl = /* tag */typeof l === "number" ? 0 : l.h;
+    var hr;
+    hr = /* tag */typeof r === "number" ? 0 : r.h;
     if (hl > (hr + 2 | 0)) {
-      if (l) {
-        var lr = l.r;
-        var lv = l.v;
-        var ll = l.l;
-        if (height(ll) >= height(lr)) {
-          return create(ll, lv, create(lr, v, r));
-        }
-        if (lr) {
-          return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
-        }
+      if (/* tag */typeof l === "number") {
         throw {
               RE_EXN_ID: "Invalid_argument",
               _1: "Set.bal",
               Error: new Error()
             };
       }
+      var lr = l.r;
+      var lv = l.v;
+      var ll = l.l;
+      if (height(ll) >= height(lr)) {
+        return create(ll, lv, create(lr, v, r));
+      }
+      if (/* tag */typeof lr !== "number") {
+        return create(create(ll, lv, lr.l), lr.v, create(lr.r, v, r));
+      }
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
@@ -56,22 +60,22 @@ function Make(Ord) {
               h: hl >= hr ? hl + 1 | 0 : hr + 1 | 0
             };
     }
-    if (r) {
-      var rr = r.r;
-      var rv = r.v;
-      var rl = r.l;
-      if (height(rr) >= height(rl)) {
-        return create(create(l, v, rl), rv, rr);
-      }
-      if (rl) {
-        return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
-      }
+    if (/* tag */typeof r === "number") {
       throw {
             RE_EXN_ID: "Invalid_argument",
             _1: "Set.bal",
             Error: new Error()
           };
     }
+    var rr = r.r;
+    var rv = r.v;
+    var rl = r.l;
+    if (height(rr) >= height(rl)) {
+      return create(create(l, v, rl), rv, rr);
+    }
+    if (/* tag */typeof rl !== "number") {
+      return create(create(l, v, rl.l), rl.v, create(rl.r, rv, rr));
+    }
     throw {
           RE_EXN_ID: "Invalid_argument",
           _1: "Set.bal",
@@ -79,7 +83,7 @@ function Make(Ord) {
         };
   };
   var add = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Node */{
               l: /* Empty */0,
               v: x,
@@ -118,28 +122,28 @@ function Make(Ord) {
           };
   };
   var add_min_element = function (x, param) {
-    if (param) {
-      return bal(add_min_element(x, param.l), param.v, param.r);
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(add_min_element(x, param.l), param.v, param.r);
     }
   };
   var add_max_element = function (x, param) {
-    if (param) {
-      return bal(param.l, param.v, add_max_element(x, param.r));
-    } else {
+    if (/* tag */typeof param === "number") {
       return singleton(x);
+    } else {
+      return bal(param.l, param.v, add_max_element(x, param.r));
     }
   };
   var join = function (l, v, r) {
-    if (!l) {
+    if (/* tag */typeof l === "number") {
       return add_min_element(v, r);
     }
-    if (!r) {
+    var lh = l.h;
+    if (/* tag */typeof r === "number") {
       return add_max_element(v, l);
     }
     var rh = r.h;
-    var lh = l.h;
     if (lh > (rh + 2 | 0)) {
       return bal(l.l, l.v, join(l.r, v, r));
     } else if (rh > (lh + 2 | 0)) {
@@ -151,28 +155,28 @@ function Make(Ord) {
   var min_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var l = param.l;
-        if (!l) {
-          return param.v;
-        }
-        _param = l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var l = param.l;
+      if (/* tag */typeof l === "number") {
+        return param.v;
+      }
+      _param = l;
+      continue ;
     };
   };
   var min_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var l = param.l;
-      if (!l) {
+      if (/* tag */typeof l === "number") {
         return Caml_option.some(param.v);
       }
       _param = l;
@@ -182,28 +186,28 @@ function Make(Ord) {
   var max_elt = function (_param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var r = param.r;
-        if (!r) {
-          return param.v;
-        }
-        _param = r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var r = param.r;
+      if (/* tag */typeof r === "number") {
+        return param.v;
+      }
+      _param = r;
+      continue ;
     };
   };
   var max_elt_opt = function (_param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var r = param.r;
-      if (!r) {
+      if (/* tag */typeof r === "number") {
         return Caml_option.some(param.v);
       }
       _param = r;
@@ -211,44 +215,40 @@ function Make(Ord) {
     };
   };
   var remove_min_elt = function (param) {
-    if (param) {
-      var l = param.l;
-      if (l) {
-        return bal(remove_min_elt(l), param.v, param.r);
-      } else {
-        return param.r;
-      }
+    if (/* tag */typeof param === "number") {
+      throw {
+            RE_EXN_ID: "Invalid_argument",
+            _1: "Set.remove_min_elt",
+            Error: new Error()
+          };
+    }
+    var l = param.l;
+    if (/* tag */typeof l === "number") {
+      return param.r;
+    } else {
+      return bal(remove_min_elt(l), param.v, param.r);
     }
-    throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "Set.remove_min_elt",
-          Error: new Error()
-        };
   };
   var merge = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return bal(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return bal(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var concat = function (t1, t2) {
-    if (t1) {
-      if (t2) {
-        return join(t1, min_elt(t2), remove_min_elt(t2));
-      } else {
-        return t1;
-      }
-    } else {
+    if (/* tag */typeof t1 === "number") {
       return t2;
+    } else if (/* tag */typeof t2 === "number") {
+      return t1;
+    } else {
+      return join(t1, min_elt(t2), remove_min_elt(t2));
     }
   };
   var split = function (x, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               false,
@@ -282,16 +282,16 @@ function Make(Ord) {
           ];
   };
   var is_empty = function (param) {
-    if (param) {
-      return false;
-    } else {
+    if (/* tag */typeof param === "number") {
       return true;
+    } else {
+      return false;
     }
   };
   var mem = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       var c = Curry._2(Ord.compare, x, param.v);
@@ -303,7 +303,7 @@ function Make(Ord) {
     };
   };
   var remove = function (x, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -329,16 +329,16 @@ function Make(Ord) {
     }
   };
   var union = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return s2;
     }
-    if (!s2) {
+    var h1 = s1.h;
+    var v1 = s1.v;
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var h2 = s2.h;
     var v2 = s2.v;
-    var h1 = s1.h;
-    var v1 = s1.v;
     if (h1 >= h2) {
       if (h2 === 1) {
         return add(v2, s1);
@@ -353,10 +353,10 @@ function Make(Ord) {
     return join(union(match$1[0], s2.l), v2, union(match$1[2], s2.r));
   };
   var inter = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return /* Empty */0;
     }
     var r1 = s1.r;
@@ -371,10 +371,10 @@ function Make(Ord) {
     }
   };
   var diff = function (s1, s2) {
-    if (!s1) {
+    if (/* tag */typeof s1 === "number") {
       return /* Empty */0;
     }
-    if (!s2) {
+    if (/* tag */typeof s2 === "number") {
       return s1;
     }
     var r1 = s1.r;
@@ -392,7 +392,7 @@ function Make(Ord) {
     while(true) {
       var e = _e;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return e;
       }
       _e = /* More */{
@@ -408,14 +408,14 @@ function Make(Ord) {
     while(true) {
       var e2 = _e2;
       var e1 = _e1;
-      if (!e1) {
-        if (e2) {
-          return -1;
-        } else {
+      if (/* tag */typeof e1 === "number") {
+        if (/* tag */typeof e2 === "number") {
           return 0;
+        } else {
+          return -1;
         }
       }
-      if (!e2) {
+      if (/* tag */typeof e2 === "number") {
         return 1;
       }
       var c = Curry._2(Ord.compare, e1._0, e2._0);
@@ -437,17 +437,17 @@ function Make(Ord) {
     while(true) {
       var s2 = _s2;
       var s1 = _s1;
-      if (!s1) {
+      if (/* tag */typeof s1 === "number") {
         return true;
       }
-      if (!s2) {
+      var r1 = s1.r;
+      var v1 = s1.v;
+      var l1 = s1.l;
+      if (/* tag */typeof s2 === "number") {
         return false;
       }
       var r2 = s2.r;
       var l2 = s2.l;
-      var r1 = s1.r;
-      var v1 = s1.v;
-      var l1 = s1.l;
       var c = Curry._2(Ord.compare, v1, s2.v);
       if (c === 0) {
         if (!subset(l1, l2)) {
@@ -484,7 +484,7 @@ function Make(Ord) {
   var iter = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       iter(f, param.l);
@@ -497,7 +497,7 @@ function Make(Ord) {
     while(true) {
       var accu = _accu;
       var s = _s;
-      if (!s) {
+      if (/* tag */typeof s === "number") {
         return accu;
       }
       _accu = Curry._2(f, s.v, fold(f, s.l, accu));
@@ -508,7 +508,7 @@ function Make(Ord) {
   var for_all = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return true;
       }
       if (!Curry._1(p, param.v)) {
@@ -524,7 +524,7 @@ function Make(Ord) {
   var exists = function (p, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return false;
       }
       if (Curry._1(p, param.v)) {
@@ -538,7 +538,7 @@ function Make(Ord) {
     };
   };
   var filter = function (p, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
@@ -558,7 +558,7 @@ function Make(Ord) {
     }
   };
   var partition = function (p, param) {
-    if (!param) {
+    if (/* tag */typeof param === "number") {
       return [
               /* Empty */0,
               /* Empty */0
@@ -585,17 +585,17 @@ function Make(Ord) {
     }
   };
   var cardinal = function (param) {
-    if (param) {
-      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
-    } else {
+    if (/* tag */typeof param === "number") {
       return 0;
+    } else {
+      return (cardinal(param.l) + 1 | 0) + cardinal(param.r) | 0;
     }
   };
   var elements_aux = function (_accu, _param) {
     while(true) {
       var param = _param;
       var accu = _accu;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return accu;
       }
       _param = param.l;
@@ -612,26 +612,26 @@ function Make(Ord) {
   var find = function (x, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        var c = Curry._2(Ord.compare, x, v);
-        if (c === 0) {
-          return v;
-        }
-        _param = c < 0 ? param.l : param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      var c = Curry._2(Ord.compare, x, v);
+      if (c === 0) {
+        return v;
+      }
+      _param = c < 0 ? param.l : param.r;
+      continue ;
     };
   };
   var find_first_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return v0;
       }
       var v = param.v;
@@ -647,25 +647,25 @@ function Make(Ord) {
   var find_first = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_first_aux(v, f, param.l);
-        }
-        _param = param.r;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_first_aux(v, f, param.l);
+      }
+      _param = param.r;
+      continue ;
     };
   };
   var find_first_opt_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return Caml_option.some(v0);
       }
       var v = param.v;
@@ -681,7 +681,7 @@ function Make(Ord) {
   var find_first_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -696,7 +696,7 @@ function Make(Ord) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return v0;
       }
       var v = param.v;
@@ -712,25 +712,25 @@ function Make(Ord) {
   var find_last = function (f, _param) {
     while(true) {
       var param = _param;
-      if (param) {
-        var v = param.v;
-        if (Curry._1(f, v)) {
-          return find_last_aux(v, f, param.r);
-        }
-        _param = param.l;
-        continue ;
+      if (/* tag */typeof param === "number") {
+        throw {
+              RE_EXN_ID: "Not_found",
+              Error: new Error()
+            };
       }
-      throw {
-            RE_EXN_ID: "Not_found",
-            Error: new Error()
-          };
+      var v = param.v;
+      if (Curry._1(f, v)) {
+        return find_last_aux(v, f, param.r);
+      }
+      _param = param.l;
+      continue ;
     };
   };
   var find_last_opt_aux = function (_v0, f, _param) {
     while(true) {
       var param = _param;
       var v0 = _v0;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return Caml_option.some(v0);
       }
       var v = param.v;
@@ -746,7 +746,7 @@ function Make(Ord) {
   var find_last_opt = function (f, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -760,7 +760,7 @@ function Make(Ord) {
   var find_opt = function (x, _param) {
     while(true) {
       var param = _param;
-      if (!param) {
+      if (/* tag */typeof param === "number") {
         return ;
       }
       var v = param.v;
@@ -780,7 +780,7 @@ function Make(Ord) {
     }
   };
   var map = function (f, t) {
-    if (!t) {
+    if (/* tag */typeof t === "number") {
       return /* Empty */0;
     }
     var r = t.r;
diff --git a/lib/js/stream.js b/lib/js/stream.js
index 7a550fbdc7..ed0f234881 100644
--- a/lib/js/stream.js
+++ b/lib/js/stream.js
@@ -31,7 +31,7 @@ function data(param) {
 function get_data(count, _d) {
   while(true) {
     var d = _d;
-    if (typeof d === "number") {
+    if (/* tag */typeof d === "number") {
       return d;
     }
     switch (d.TAG | 0) {
@@ -40,7 +40,7 @@ function get_data(count, _d) {
       case /* Sapp */1 :
           var d2 = d._1;
           var match = get_data(count, d._0);
-          if (typeof match === "number") {
+          if (/* tag */typeof match === "number") {
             _d = d2;
             continue ;
           }
@@ -102,7 +102,7 @@ function get_data(count, _d) {
 function peek_data(s) {
   while(true) {
     var f = s.data;
-    if (typeof f === "number") {
+    if (/* tag */typeof f === "number") {
       return ;
     }
     switch (f.TAG | 0) {
@@ -110,7 +110,7 @@ function peek_data(s) {
           return Caml_option.some(f._0);
       case /* Sapp */1 :
           var d = get_data(s.count, s.data);
-          if (typeof d === "number") {
+          if (/* tag */typeof d === "number") {
             return ;
           }
           if (d.TAG === /* Scons */0) {
@@ -153,7 +153,7 @@ function peek(s) {
 function junk_data(s) {
   while(true) {
     var g = s.data;
-    if (typeof g !== "number") {
+    if (/* tag */typeof g !== "number") {
       switch (g.TAG | 0) {
         case /* Scons */0 :
             s.count = s.count + 1 | 0;
@@ -428,7 +428,7 @@ function slazy(f) {
 }
 
 function dump_data(f, param) {
-  if (typeof param === "number") {
+  if (/* tag */typeof param === "number") {
     console.log("Sempty");
     return ;
   }