diff --git a/CHANGELOG.md b/CHANGELOG.md
index e9bbc2ec47..011296205e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@
 - Ast cleanup: explicit representation for optional record fields in types. https://github.com/rescript-lang/rescript/pull/7190 https://github.com/rescript-lang/rescript/pull/7191
 - AST cleanup: first-class expression and patterns for records with optional fields. https://github.com/rescript-lang/rescript/pull/7192
 - AST cleanup: Represent the arity of uncurried function definitions directly in the AST. https://github.com/rescript-lang/rescript/pull/7197
+- AST cleanup: Remove Pexp_function from the AST. https://github.com/rescript-lang/rescript/pull/7198
 
 
 # 12.0.0-alpha.5
diff --git a/analysis/reanalyze/src/Arnold.ml b/analysis/reanalyze/src/Arnold.ml
index 7c56cecaf8..f9598cd0dc 100644
--- a/analysis/reanalyze/src/Arnold.ml
+++ b/analysis/reanalyze/src/Arnold.ml
@@ -908,7 +908,7 @@ module Compile = struct
         let open Command in
         c +++ ConstrOption Rnone
       | _ -> c)
-    | Texp_function {cases} -> cases |> List.map (case ~ctx) |> Command.nondet
+    | Texp_function {case = case_} -> case ~ctx case_
     | Texp_match (e, casesOk, casesExn, _partial)
       when not
              (casesExn
diff --git a/analysis/reanalyze/src/DeadValue.ml b/analysis/reanalyze/src/DeadValue.ml
index ef3ab19018..9e102cba52 100644
--- a/analysis/reanalyze/src/DeadValue.ml
+++ b/analysis/reanalyze/src/DeadValue.ml
@@ -156,18 +156,16 @@ let rec collectExpr super self (e : Typedtree.expression) =
           exp_desc =
             Texp_function
               {
-                cases =
-                  [
-                    {
-                      c_lhs = {pat_desc = Tpat_var (etaArg, _)};
-                      c_rhs =
-                        {
-                          exp_desc =
-                            Texp_apply
-                              ({exp_desc = Texp_ident (idArg2, _, _)}, args);
-                        };
-                    };
-                  ];
+                case =
+                  {
+                    c_lhs = {pat_desc = Tpat_var (etaArg, _)};
+                    c_rhs =
+                      {
+                        exp_desc =
+                          Texp_apply
+                            ({exp_desc = Texp_ident (idArg2, _, _)}, args);
+                      };
+                  };
               };
         } )
     when Ident.name idArg = "arg"
diff --git a/analysis/src/DocumentSymbol.ml b/analysis/src/DocumentSymbol.ml
index 44580f1e68..0e5b982b5b 100644
--- a/analysis/src/DocumentSymbol.ml
+++ b/analysis/src/DocumentSymbol.ml
@@ -41,7 +41,6 @@ let command ~path =
   let rec exprKind (exp : Parsetree.expression) =
     match exp.pexp_desc with
     | Pexp_fun _ -> Function
-    | Pexp_function _ -> Function
     | Pexp_constraint (e, _) -> exprKind e
     | Pexp_constant (Pconst_string _) -> String
     | Pexp_constant (Pconst_float _ | Pconst_integer _) -> Number
diff --git a/analysis/src/Utils.ml b/analysis/src/Utils.ml
index 43117e4f78..127ceef0f3 100644
--- a/analysis/src/Utils.ml
+++ b/analysis/src/Utils.ml
@@ -85,7 +85,6 @@ let identifyPexp pexp =
   | Parsetree.Pexp_ident _ -> "Pexp_ident"
   | Pexp_constant _ -> "Pexp_constant"
   | Pexp_let _ -> "Pexp_let"
-  | Pexp_function _ -> "Pexp_function"
   | Pexp_fun _ -> "Pexp_fun"
   | Pexp_apply _ -> "Pexp_apply"
   | Pexp_match _ -> "Pexp_match"
diff --git a/compiler/frontend/bs_ast_mapper.ml b/compiler/frontend/bs_ast_mapper.ml
index f63531e6b2..78adb57b4c 100644
--- a/compiler/frontend/bs_ast_mapper.ml
+++ b/compiler/frontend/bs_ast_mapper.ml
@@ -319,7 +319,6 @@ module E = struct
       fun_ ~loc ~attrs ~arity lab
         (map_opt (sub.expr sub) def)
         (sub.pat sub p) (sub.expr sub e)
-    | Pexp_function pel -> function_ ~loc ~attrs (sub.cases sub pel)
     | Pexp_apply (e, l) ->
       apply ~loc ~attrs (sub.expr sub e) (List.map (map_snd (sub.expr sub)) l)
     | Pexp_match (e, pel) ->
diff --git a/compiler/frontend/bs_builtin_ppx.ml b/compiler/frontend/bs_builtin_ppx.ml
index 5a0c31d22d..a770992366 100644
--- a/compiler/frontend/bs_builtin_ppx.ml
+++ b/compiler/frontend/bs_builtin_ppx.ml
@@ -110,9 +110,6 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
   | Pexp_constant (Pconst_integer (s, Some 'l')) ->
     {e with pexp_desc = Pexp_constant (Pconst_integer (s, None))}
   (* End rewriting *)
-  | Pexp_function _ ->
-    async_context := false;
-    default_expr_mapper self e
   | _
     when Ast_uncurried.expr_is_uncurried_fun e
          &&
diff --git a/compiler/gentype/TranslateStructure.ml b/compiler/gentype/TranslateStructure.ml
index 15d24f0731..8cab0461b4 100644
--- a/compiler/gentype/TranslateStructure.ml
+++ b/compiler/gentype/TranslateStructure.ml
@@ -3,9 +3,8 @@ open GenTypeCommon
 let rec addAnnotationsToTypes_ ~config ~(expr : Typedtree.expression)
     (arg_types : arg_type list) =
   match (expr.exp_desc, expr.exp_type.desc, arg_types) with
-  | ( Texp_function {arg_label; param; cases = [{c_rhs}]},
-      _,
-      {a_type} :: next_types ) ->
+  | Texp_function {arg_label; param; case = {c_rhs}}, _, {a_type} :: next_types
+    ->
     let next_types1 =
       next_types |> addAnnotationsToTypes_ ~config ~expr:c_rhs
     in
@@ -51,7 +50,7 @@ and add_annotations_to_fields ~config (expr : Typedtree.expression)
     (fields : fields) (arg_types : arg_type list) =
   match (expr.exp_desc, fields, arg_types) with
   | _, [], _ -> ([], arg_types |> add_annotations_to_types ~config ~expr)
-  | Texp_function {cases = [{c_rhs}]}, field :: next_fields, _ ->
+  | Texp_function {case = {c_rhs}}, field :: next_fields, _ ->
     let next_fields1, types1 =
       add_annotations_to_fields ~config c_rhs next_fields arg_types
     in
diff --git a/compiler/ml/ast_helper.ml b/compiler/ml/ast_helper.ml
index 01c5ea0e13..21bb38554f 100644
--- a/compiler/ml/ast_helper.ml
+++ b/compiler/ml/ast_helper.ml
@@ -152,7 +152,6 @@ module Exp = struct
   let let_ ?loc ?attrs a b c = mk ?loc ?attrs (Pexp_let (a, b, c))
   let fun_ ?loc ?attrs ~arity a b c d =
     mk ?loc ?attrs (Pexp_fun (a, b, c, d, arity))
-  let function_ ?loc ?attrs a = mk ?loc ?attrs (Pexp_function a)
   let apply ?loc ?attrs a b = mk ?loc ?attrs (Pexp_apply (a, b))
   let match_ ?loc ?attrs a b = mk ?loc ?attrs (Pexp_match (a, b))
   let try_ ?loc ?attrs a b = mk ?loc ?attrs (Pexp_try (a, b))
diff --git a/compiler/ml/ast_helper.mli b/compiler/ml/ast_helper.mli
index cfb761485d..62ee9276a3 100644
--- a/compiler/ml/ast_helper.mli
+++ b/compiler/ml/ast_helper.mli
@@ -138,7 +138,6 @@ module Exp : sig
     pattern ->
     expression ->
     expression
-  val function_ : ?loc:loc -> ?attrs:attrs -> case list -> expression
   val apply :
     ?loc:loc ->
     ?attrs:attrs ->
diff --git a/compiler/ml/ast_iterator.ml b/compiler/ml/ast_iterator.ml
index 6f20cd9650..8f64d484c8 100644
--- a/compiler/ml/ast_iterator.ml
+++ b/compiler/ml/ast_iterator.ml
@@ -286,7 +286,6 @@ module E = struct
       iter_opt (sub.expr sub) def;
       sub.pat sub p;
       sub.expr sub e
-    | Pexp_function pel -> sub.cases sub pel
     | Pexp_apply (e, l) ->
       sub.expr sub e;
       List.iter (iter_snd (sub.expr sub)) l
diff --git a/compiler/ml/ast_mapper.ml b/compiler/ml/ast_mapper.ml
index 83fb0c0e56..383e9a47bd 100644
--- a/compiler/ml/ast_mapper.ml
+++ b/compiler/ml/ast_mapper.ml
@@ -282,7 +282,6 @@ module E = struct
       fun_ ~loc ~attrs ~arity lab
         (map_opt (sub.expr sub) def)
         (sub.pat sub p) (sub.expr sub e)
-    | Pexp_function pel -> function_ ~loc ~attrs (sub.cases sub pel)
     | Pexp_apply (e, l) ->
       apply ~loc ~attrs (sub.expr sub e) (List.map (map_snd (sub.expr sub)) l)
     | Pexp_match (e, pel) ->
diff --git a/compiler/ml/ast_mapper_from0.ml b/compiler/ml/ast_mapper_from0.ml
index 036ecb3755..051517062c 100644
--- a/compiler/ml/ast_mapper_from0.ml
+++ b/compiler/ml/ast_mapper_from0.ml
@@ -288,7 +288,7 @@ module E = struct
       fun_ ~loc ~attrs ~arity:None lab
         (map_opt (sub.expr sub) def)
         (sub.pat sub p) (sub.expr sub e)
-    | Pexp_function pel -> function_ ~loc ~attrs (sub.cases sub pel)
+    | Pexp_function _ -> assert false
     | Pexp_apply (e, l) ->
       apply ~loc ~attrs (sub.expr sub e) (List.map (map_snd (sub.expr sub)) l)
     | Pexp_match (e, pel) ->
diff --git a/compiler/ml/ast_mapper_to0.ml b/compiler/ml/ast_mapper_to0.ml
index 260b0de940..c45974a95d 100644
--- a/compiler/ml/ast_mapper_to0.ml
+++ b/compiler/ml/ast_mapper_to0.ml
@@ -287,7 +287,6 @@ module E = struct
       fun_ ~loc ~attrs lab
         (map_opt (sub.expr sub) def)
         (sub.pat sub p) (sub.expr sub e)
-    | Pexp_function pel -> function_ ~loc ~attrs (sub.cases sub pel)
     | Pexp_apply (e, l) ->
       apply ~loc ~attrs (sub.expr sub e) (List.map (map_snd (sub.expr sub)) l)
     | Pexp_match (e, pel) ->
diff --git a/compiler/ml/depend.ml b/compiler/ml/depend.ml
index a2c4e04b40..7d48262a79 100644
--- a/compiler/ml/depend.ml
+++ b/compiler/ml/depend.ml
@@ -221,7 +221,6 @@ let rec add_expr bv exp =
   | Pexp_fun (_, opte, p, e, _) ->
     add_opt add_expr bv opte;
     add_expr (add_pattern bv p) e
-  | Pexp_function pel -> add_cases bv pel
   | Pexp_apply (e, el) ->
     add_expr bv e;
     List.iter (fun (_, e) -> add_expr bv e) el
diff --git a/compiler/ml/parsetree.ml b/compiler/ml/parsetree.ml
index 060f9cf5b4..de6c4f0eec 100644
--- a/compiler/ml/parsetree.ml
+++ b/compiler/ml/parsetree.ml
@@ -224,7 +224,6 @@ and expression_desc =
     (* let P1 = E1 and ... and Pn = EN in E       (flag = Nonrecursive)
        let rec P1 = E1 and ... and Pn = EN in E   (flag = Recursive)
     *)
-  | Pexp_function of case list (* function P1 -> E1 | ... | Pn -> En *)
   | Pexp_fun of
       arg_label * expression option * pattern * expression * int option
     (* fun P -> E1                          (Simple, None)
diff --git a/compiler/ml/pprintast.ml b/compiler/ml/pprintast.ml
index a360d3dfe6..2f3de443c7 100644
--- a/compiler/ml/pprintast.ml
+++ b/compiler/ml/pprintast.ml
@@ -535,7 +535,7 @@ and expression ctxt f x =
     pp f "((%a)@,%a)" (expression ctxt) {x with pexp_attributes=[]}
       (attributes ctxt) x.pexp_attributes
   else match x.pexp_desc with
-    | Pexp_function _ | Pexp_fun _ | Pexp_match _ | Pexp_try _ | Pexp_sequence _
+    | Pexp_fun _ | Pexp_match _ | Pexp_try _ | Pexp_sequence _
       when ctxt.pipe || ctxt.semi ->
         paren true (expression reset_ctxt) f x
     | Pexp_ifthenelse _ | Pexp_sequence _ when ctxt.ifthenelse ->
@@ -551,8 +551,6 @@ and expression ctxt f x =
         pp f "@[<2>fun@;%s%a->@;%a@]"
           arity_str (label_exp ctxt) (l, e0, p)
           (expression ctxt) e
-    | Pexp_function l ->
-        pp f "@[<hv>function%a@]" (case_list ctxt) l
     | Pexp_match (e, l) ->
         pp f "@[<hv0>@[<hv0>@[<2>match %a@]@ with@]%a@]"
           (expression reset_ctxt) e (case_list ctxt) l
diff --git a/compiler/ml/printast.ml b/compiler/ml/printast.ml
index a635fc0498..385c88f4fe 100644
--- a/compiler/ml/printast.ml
+++ b/compiler/ml/printast.ml
@@ -233,9 +233,6 @@ and expression i ppf x =
     line i ppf "Pexp_let %a\n" fmt_rec_flag rf;
     list i value_binding ppf l;
     expression i ppf e
-  | Pexp_function l ->
-    line i ppf "Pexp_function\n";
-    list i case ppf l
   | Pexp_fun (l, eo, p, e, arity) ->
     line i ppf "Pexp_fun\n";
     let () =
diff --git a/compiler/ml/printtyped.ml b/compiler/ml/printtyped.ml
index 6303411246..1451266b2b 100644
--- a/compiler/ml/printtyped.ml
+++ b/compiler/ml/printtyped.ml
@@ -285,11 +285,11 @@ and expression i ppf x =
     line i ppf "Texp_let %a\n" fmt_rec_flag rf;
     list i value_binding ppf l;
     expression i ppf e
-  | Texp_function {arg_label = p; param; cases; partial = _} ->
+  | Texp_function {arg_label = p; param; case = case_; partial = _} ->
     line i ppf "Texp_function\n";
     line i ppf "%a" Ident.print param;
     arg_label i ppf p;
-    list i case ppf cases
+    case i ppf case_
   | Texp_apply (e, l) ->
     line i ppf "Texp_apply\n";
     expression i ppf e;
diff --git a/compiler/ml/rec_check.ml b/compiler/ml/rec_check.ml
index a88b27ed7f..a669915a57 100644
--- a/compiler/ml/rec_check.ml
+++ b/compiler/ml/rec_check.ml
@@ -292,8 +292,8 @@ let rec expression : Env.env -> Typedtree.expression -> Use.t =
     let case env {Typedtree.c_rhs} = expression env c_rhs in
     Use.join (expression env e) (list case env cases)
   | Texp_override () -> assert false
-  | Texp_function {cases} ->
-    Use.delay (list (case ~scrutinee:Use.empty) env cases)
+  | Texp_function {case = case_} ->
+    Use.delay (list (case ~scrutinee:Use.empty) env [case_])
   | Texp_lazy e -> (
     match Typeopt.classify_lazy_argument e with
     | `Constant_or_function | `Identifier _ | `Float -> expression env e
diff --git a/compiler/ml/tast_iterator.ml b/compiler/ml/tast_iterator.ml
index ce947feb3e..b925d49336 100644
--- a/compiler/ml/tast_iterator.ml
+++ b/compiler/ml/tast_iterator.ml
@@ -155,7 +155,7 @@ let expr sub {exp_extra; exp_desc; exp_env; _} =
   | Texp_let (rec_flag, list, exp) ->
     sub.value_bindings sub (rec_flag, list);
     sub.expr sub exp
-  | Texp_function {cases; _} -> sub.cases sub cases
+  | Texp_function {case; _} -> sub.case sub case
   | Texp_apply (exp, list) ->
     sub.expr sub exp;
     List.iter (fun (_, o) -> Option.iter (sub.expr sub) o) list
diff --git a/compiler/ml/tast_mapper.ml b/compiler/ml/tast_mapper.ml
index 8d21406bd4..7a60dcf449 100644
--- a/compiler/ml/tast_mapper.ml
+++ b/compiler/ml/tast_mapper.ml
@@ -199,8 +199,8 @@ let expr sub x =
     | Texp_let (rec_flag, list, exp) ->
       let rec_flag, list = sub.value_bindings sub (rec_flag, list) in
       Texp_let (rec_flag, list, sub.expr sub exp)
-    | Texp_function {arg_label; param; cases; partial} ->
-      Texp_function {arg_label; param; cases = sub.cases sub cases; partial}
+    | Texp_function {arg_label; arity; param; case; partial} ->
+      Texp_function {arg_label; arity; param; case = sub.case sub case; partial}
     | Texp_apply (exp, list) ->
       Texp_apply
         (sub.expr sub exp, List.map (tuple2 id (opt (sub.expr sub))) list)
diff --git a/compiler/ml/translcore.ml b/compiler/ml/translcore.ml
index 1fdb458a0a..59febcda45 100644
--- a/compiler/ml/translcore.ml
+++ b/compiler/ml/translcore.ml
@@ -549,58 +549,54 @@ type binding =
   | Bind_value of value_binding list
   | Bind_module of Ident.t * string loc * module_expr
 
-let rec push_defaults loc bindings cases partial =
-  match cases with
-  | [
-   {
-     c_lhs = pat;
-     c_guard = None;
-     c_rhs =
-       {exp_desc = Texp_function {arg_label; param; cases; partial}} as exp;
-   };
-  ] ->
-    let cases = push_defaults exp.exp_loc bindings cases partial in
-    [
-      {
-        c_lhs = pat;
-        c_guard = None;
-        c_rhs =
-          {exp with exp_desc = Texp_function {arg_label; param; cases; partial}};
-      };
-    ]
-  | [
-   {
-     c_lhs = pat;
-     c_guard = None;
-     c_rhs =
-       {
-         exp_attributes = [({txt = "#default"}, _)];
-         exp_desc =
-           Texp_let (Nonrecursive, binds, ({exp_desc = Texp_function _} as e2));
-       };
-   };
-  ] ->
+let rec push_defaults loc bindings case partial =
+  match case with
+  | {
+   c_lhs = pat;
+   c_guard = None;
+   c_rhs =
+     {exp_desc = Texp_function {arg_label; arity; param; case; partial}} as exp;
+  } ->
+    let case = push_defaults exp.exp_loc bindings case partial in
+
+    {
+      c_lhs = pat;
+      c_guard = None;
+      c_rhs =
+        {
+          exp with
+          exp_desc = Texp_function {arg_label; arity; param; case; partial};
+        };
+    }
+  | {
+   c_lhs = pat;
+   c_guard = None;
+   c_rhs =
+     {
+       exp_attributes = [({txt = "#default"}, _)];
+       exp_desc =
+         Texp_let (Nonrecursive, binds, ({exp_desc = Texp_function _} as e2));
+     };
+  } ->
     push_defaults loc
       (Bind_value binds :: bindings)
-      [{c_lhs = pat; c_guard = None; c_rhs = e2}]
+      {c_lhs = pat; c_guard = None; c_rhs = e2}
       partial
-  | [
-   {
-     c_lhs = pat;
-     c_guard = None;
-     c_rhs =
-       {
-         exp_attributes = [({txt = "#modulepat"}, _)];
-         exp_desc =
-           Texp_letmodule (id, name, mexpr, ({exp_desc = Texp_function _} as e2));
-       };
-   };
-  ] ->
+  | {
+   c_lhs = pat;
+   c_guard = None;
+   c_rhs =
+     {
+       exp_attributes = [({txt = "#modulepat"}, _)];
+       exp_desc =
+         Texp_letmodule (id, name, mexpr, ({exp_desc = Texp_function _} as e2));
+     };
+  } ->
     push_defaults loc
       (Bind_module (id, name, mexpr) :: bindings)
-      [{c_lhs = pat; c_guard = None; c_rhs = e2}]
+      {c_lhs = pat; c_guard = None; c_rhs = e2}
       partial
-  | [case] ->
+  | case ->
     let exp =
       List.fold_left
         (fun exp binds ->
@@ -614,45 +610,7 @@ let rec push_defaults loc bindings cases partial =
           })
         case.c_rhs bindings
     in
-    [{case with c_rhs = exp}]
-  | {c_lhs = pat; c_rhs = exp; c_guard = _} :: _ when bindings <> [] ->
-    let param = Typecore.name_pattern "param" cases in
-    let name = Ident.name param in
-    let exp =
-      {
-        exp with
-        exp_loc = loc;
-        exp_desc =
-          Texp_match
-            ( {
-                exp with
-                exp_type = pat.pat_type;
-                exp_desc =
-                  Texp_ident
-                    ( Path.Pident param,
-                      mknoloc (Longident.Lident name),
-                      {
-                        val_type = pat.pat_type;
-                        val_kind = Val_reg;
-                        val_attributes = [];
-                        Types.val_loc = Location.none;
-                      } );
-              },
-              cases,
-              [],
-              partial );
-      }
-    in
-    push_defaults loc bindings
-      [
-        {
-          c_lhs = {pat with pat_desc = Tpat_var (param, mknoloc name)};
-          c_guard = None;
-          c_rhs = exp;
-        };
-      ]
-      Total
-  | _ -> cases
+    {case with c_rhs = exp}
 
 (* Assertions *)
 
@@ -716,7 +674,7 @@ and transl_exp0 (e : Typedtree.expression) : Lambda.lambda =
   | Texp_constant cst -> Lconst (Const_base cst)
   | Texp_let (rec_flag, pat_expr_list, body) ->
     transl_let rec_flag pat_expr_list (transl_exp body)
-  | Texp_function {arg_label = _; param; cases; partial} ->
+  | Texp_function {arg_label = _; param; case; partial} ->
     let async = has_async_attribute e in
     let directive =
       match extract_directive_for_fn e with
@@ -724,7 +682,7 @@ and transl_exp0 (e : Typedtree.expression) : Lambda.lambda =
       | Some (directive, _) -> Some directive
     in
     let params, body, return_unit =
-      let pl = push_defaults e.exp_loc [] cases partial in
+      let pl = push_defaults e.exp_loc [] case partial in
       transl_function e.exp_loc partial param pl
     in
     let attr =
@@ -1088,32 +1046,28 @@ and transl_apply ?(inlined = Default_inline)
           sargs)
       : Lambda.lambda)
 
-and transl_function loc partial param cases =
-  match cases with
-  | [
-   {
-     c_lhs = pat;
-     c_guard = None;
-     c_rhs =
-       {
-         exp_desc =
-           Texp_function
-             {arg_label = _; param = param'; cases; partial = partial'};
-       } as exp;
-   };
-  ]
+and transl_function loc partial param case =
+  match case with
+  | {
+   c_lhs = pat;
+   c_guard = None;
+   c_rhs =
+     {
+       exp_desc =
+         Texp_function {arg_label = _; param = param'; case; partial = partial'};
+     } as exp;
+  }
     when Parmatch.inactive ~partial pat && not (exp |> has_async_attribute) ->
     let params, body, return_unit =
-      transl_function exp.exp_loc partial' param' cases
+      transl_function exp.exp_loc partial' param' case
     in
     ( param :: params,
       Matching.for_function loc None (Lvar param) [(pat, body)] partial,
       return_unit )
-  | {c_rhs = {exp_env; exp_type}; _} :: _ ->
+  | {c_rhs = {exp_env; exp_type}; _} ->
     ( [param],
-      Matching.for_function loc None (Lvar param) (transl_cases cases) partial,
+      Matching.for_function loc None (Lvar param) [transl_case case] partial,
       is_base_type exp_env exp_type Predef.path_unit )
-  | _ -> assert false
 
 and transl_let rec_flag pat_expr_list body =
   match rec_flag with
diff --git a/compiler/ml/typecore.ml b/compiler/ml/typecore.ml
index fba16114be..992e64403d 100644
--- a/compiler/ml/typecore.ml
+++ b/compiler/ml/typecore.ml
@@ -137,7 +137,6 @@ let iter_expression f e =
     | Pexp_extension _ (* we don't iterate under extension point *)
     | Pexp_ident _ | Pexp_new _ | Pexp_constant _ ->
       ()
-    | Pexp_function pel -> List.iter case pel
     | Pexp_fun (_, eo, _, e, _) ->
       may expr eo;
       expr e
@@ -1917,8 +1916,6 @@ let rec type_approx env sexp =
   | Pexp_fun (p, _, _, e, _arity) ->
     let ty = if is_optional p then type_option (newvar ()) else newvar () in
     newty (Tarrow (p, ty, type_approx env e, Cok))
-  | Pexp_function ({pc_rhs = e} :: _) ->
-    newty (Tarrow (Nolabel, newvar (), type_approx env e, Cok))
   | Pexp_match (_, {pc_rhs = e} :: _) -> type_approx env e
   | Pexp_try (e, _) -> type_approx env e
   | Pexp_tuple l -> newty (Ttuple (List.map (type_approx env) l))
@@ -2374,7 +2371,7 @@ and type_expect_ ?type_clash_context ?in_function ?(recarg = Rejected) env sexp
         exp_attributes = sexp.pexp_attributes;
         exp_env = env;
       }
-  | Pexp_fun (l, Some default, spat, sbody, _arity) ->
+  | Pexp_fun (l, Some default, spat, sbody, arity) ->
     assert (is_optional l);
     (* default allowed only with optional argument *)
     let open Ast_helper in
@@ -2412,14 +2409,11 @@ and type_expect_ ?type_clash_context ?in_function ?(recarg = Rejected) env sexp
         [Vb.mk spat smatch]
         sbody
     in
-    type_function ?in_function loc sexp.pexp_attributes env ty_expected l
+    type_function ?in_function ~arity loc sexp.pexp_attributes env ty_expected l
       [Exp.case pat body]
-  | Pexp_fun (l, None, spat, sbody, _arity) ->
-    type_function ?in_function loc sexp.pexp_attributes env ty_expected l
+  | Pexp_fun (l, None, spat, sbody, arity) ->
+    type_function ?in_function ~arity loc sexp.pexp_attributes env ty_expected l
       [Ast_helper.Exp.case spat sbody]
-  | Pexp_function caselist ->
-    type_function ?in_function loc sexp.pexp_attributes env ty_expected Nolabel
-      caselist
   | Pexp_apply (sfunct, sargs) ->
     assert (sargs <> []);
     begin_def ();
@@ -3279,7 +3273,7 @@ and type_expect_ ?type_clash_context ?in_function ?(recarg = Rejected) env sexp
   | Pexp_extension ext ->
     raise (Error_forward (Builtin_attributes.error_of_extension ext))
 
-and type_function ?in_function loc attrs env ty_expected l caselist =
+and type_function ?in_function ~arity loc attrs env ty_expected l caselist =
   let loc_fun, ty_fun =
     match in_function with
     | Some p -> p
@@ -3312,13 +3306,14 @@ and type_function ?in_function loc attrs env ty_expected l caselist =
     type_cases ~in_function:(loc_fun, ty_fun) env ty_arg ty_res true loc
       caselist
   in
+  let case = List.hd cases in
   if is_optional l && not_function env ty_res then
-    Location.prerr_warning (List.hd cases).c_lhs.pat_loc
+    Location.prerr_warning case.c_lhs.pat_loc
       Warnings.Unerasable_optional_argument;
   let param = name_pattern "param" cases in
   re
     {
-      exp_desc = Texp_function {arg_label = l; param; cases; partial};
+      exp_desc = Texp_function {arg_label = l; arity; param; case; partial};
       exp_loc = loc;
       exp_extra = [];
       exp_type = instance env (newgenty (Tarrow (l, ty_arg, ty_res, Cok)));
@@ -3409,119 +3404,9 @@ and type_label_exp ?type_clash_context create env loc ty_expected
 
 and type_argument ?type_clash_context ?recarg env sarg ty_expected' ty_expected
     =
-  (* ty_expected' may be generic *)
-  let no_labels ty =
-    let ls, tvar = list_labels env ty in
-    (not tvar) && List.for_all (fun x -> x = Nolabel) ls
-  in
-  let rec is_inferred sexp =
-    match sexp.pexp_desc with
-    | Pexp_ident _ | Pexp_apply _ | Pexp_field _ | Pexp_constraint _
-    | Pexp_coerce _ | Pexp_send _ | Pexp_new _ ->
-      true
-    | Pexp_sequence (_, e) | Pexp_open (_, _, e) -> is_inferred e
-    | Pexp_ifthenelse (_, e1, Some e2) -> is_inferred e1 && is_inferred e2
-    | _ -> false
-  in
-  match expand_head env ty_expected' with
-  | {desc = Tarrow (Nolabel, ty_arg, ty_res, _); level = _}
-    when is_inferred sarg ->
-    (* apply optional arguments when expected type is "" *)
-    (* we must be very careful about not breaking the semantics *)
-    let texp = type_exp env sarg in
-    let rec make_args args ty_fun =
-      match (expand_head env ty_fun).desc with
-      | Tarrow (l, ty_arg, ty_fun, _) when is_optional l ->
-        let ty = option_none (instance env ty_arg) sarg.pexp_loc in
-        make_args ((l, Some ty) :: args) ty_fun
-      | Tarrow (Nolabel, _, ty_res', _) ->
-        (List.rev args, ty_fun, no_labels ty_res')
-      | Tvar _ -> (List.rev args, ty_fun, false)
-      | _ -> ([], texp.exp_type, false)
-    in
-    let args, ty_fun', simple_res = make_args [] texp.exp_type in
-    let texp = {texp with exp_type = instance env texp.exp_type}
-    and ty_fun = instance env ty_fun' in
-    if not (simple_res || no_labels ty_res) then (
-      unify_exp env texp ty_expected;
-      texp)
-    else (
-      unify_exp env {texp with exp_type = ty_fun} ty_expected;
-      if args = [] then texp
-      else
-        (* eta-expand to avoid side effects *)
-        let var_pair name ty =
-          let id = Ident.create name in
-          ( {
-              pat_desc = Tpat_var (id, mknoloc name);
-              pat_type = ty;
-              pat_extra = [];
-              pat_attributes = [];
-              pat_loc = Location.none;
-              pat_env = env;
-            },
-            {
-              exp_type = ty;
-              exp_loc = Location.none;
-              exp_env = env;
-              exp_extra = [];
-              exp_attributes = [];
-              exp_desc =
-                Texp_ident
-                  ( Path.Pident id,
-                    mknoloc (Longident.Lident name),
-                    {
-                      val_type = ty;
-                      val_kind = Val_reg;
-                      val_attributes = [];
-                      Types.val_loc = Location.none;
-                    } );
-            } )
-        in
-        let eta_pat, eta_var = var_pair "eta" ty_arg in
-        let func texp =
-          let e =
-            {
-              texp with
-              exp_type = ty_res;
-              exp_desc = Texp_apply (texp, args @ [(Nolabel, Some eta_var)]);
-            }
-          in
-          let cases = [case eta_pat e] in
-          let param = name_pattern "param" cases in
-          {
-            texp with
-            exp_type = ty_fun;
-            exp_desc =
-              Texp_function {arg_label = Nolabel; param; cases; partial = Total};
-          }
-        in
-        Location.prerr_warning texp.exp_loc
-          (Warnings.Eliminated_optional_arguments
-             (List.map (fun (l, _) -> Printtyp.string_of_label l) args));
-        (* let-expand to have side effects *)
-        let let_pat, let_var = var_pair "arg" texp.exp_type in
-        re
-          {
-            texp with
-            exp_type = ty_fun;
-            exp_desc =
-              Texp_let
-                ( Nonrecursive,
-                  [
-                    {
-                      vb_pat = let_pat;
-                      vb_expr = texp;
-                      vb_attributes = [];
-                      vb_loc = Location.none;
-                    };
-                  ],
-                  func let_var );
-          })
-  | _ ->
-    let texp = type_expect ?type_clash_context ?recarg env sarg ty_expected' in
-    unify_exp ?type_clash_context env texp ty_expected;
-    texp
+  let texp = type_expect ?type_clash_context ?recarg env sarg ty_expected' in
+  unify_exp ?type_clash_context env texp ty_expected;
+  texp
 
 and is_automatic_curried_application env funct =
   (* When a curried function is used with uncurried application, treat it as a curried application *)
diff --git a/compiler/ml/typedtree.ml b/compiler/ml/typedtree.ml
index c5243bcb16..571dc3f4d6 100644
--- a/compiler/ml/typedtree.ml
+++ b/compiler/ml/typedtree.ml
@@ -78,8 +78,9 @@ and expression_desc =
   | Texp_let of rec_flag * value_binding list * expression
   | Texp_function of {
       arg_label: arg_label;
+      arity: int option;
       param: Ident.t;
-      cases: case list;
+      case: case;
       partial: partial;
     }
   | Texp_apply of expression * (arg_label * expression option) list
diff --git a/compiler/ml/typedtree.mli b/compiler/ml/typedtree.mli
index e1f6548507..a0d9844574 100644
--- a/compiler/ml/typedtree.mli
+++ b/compiler/ml/typedtree.mli
@@ -132,8 +132,9 @@ and expression_desc =
          *)
   | Texp_function of {
       arg_label: arg_label;
+      arity: int option;
       param: Ident.t;
-      cases: case list;
+      case: case;
       partial: partial;
     }
       (** [Pexp_fun] and [Pexp_function] both translate to [Texp_function].
diff --git a/compiler/ml/typedtreeIter.ml b/compiler/ml/typedtreeIter.ml
index b4500cd6c1..858f7da4ca 100644
--- a/compiler/ml/typedtreeIter.ml
+++ b/compiler/ml/typedtreeIter.ml
@@ -230,7 +230,7 @@ end = struct
     | Texp_let (rec_flag, list, exp) ->
       iter_bindings rec_flag list;
       iter_expression exp
-    | Texp_function {cases; _} -> iter_cases cases
+    | Texp_function {case; _} -> iter_case case
     | Texp_apply (exp, list) ->
       iter_expression exp;
       List.iter
diff --git a/compiler/syntax/src/res_ast_debugger.ml b/compiler/syntax/src/res_ast_debugger.ml
index 0a6cf69a12..5b670076bc 100644
--- a/compiler/syntax/src/res_ast_debugger.ml
+++ b/compiler/syntax/src/res_ast_debugger.ml
@@ -558,9 +558,6 @@ module SexpAst = struct
             Sexp.list (map_empty ~f:value_binding vbs);
             expression expr;
           ]
-      | Pexp_function cases ->
-        Sexp.list
-          [Sexp.atom "Pexp_function"; Sexp.list (map_empty ~f:case cases)]
       | Pexp_fun (arg_lbl, expr_opt, pat, expr, _) ->
         Sexp.list
           [
diff --git a/compiler/syntax/src/res_parens.ml b/compiler/syntax/src/res_parens.ml
index 10f63a1167..cb5a8b0ccc 100644
--- a/compiler/syntax/src/res_parens.ml
+++ b/compiler/syntax/src/res_parens.ml
@@ -51,8 +51,8 @@ let call_expr expr =
     | {
      pexp_desc =
        ( Pexp_lazy _ | Pexp_assert _ | Pexp_fun _ | Pexp_newtype _
-       | Pexp_function _ | Pexp_constraint _ | Pexp_setfield _ | Pexp_match _
-       | Pexp_try _ | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
+       | Pexp_constraint _ | Pexp_setfield _ | Pexp_match _ | Pexp_try _
+       | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
     } ->
       Parenthesized
     | _ when Ast_uncurried.expr_is_uncurried_fun expr -> Parenthesized
@@ -104,7 +104,7 @@ let unary_expr_operand expr =
     | {
      pexp_desc =
        ( Pexp_lazy _ | Pexp_assert _ | Pexp_fun _ | Pexp_newtype _
-       | Pexp_function _ | Pexp_constraint _ | Pexp_setfield _
+       | Pexp_constraint _ | Pexp_setfield _
        | Pexp_extension _ (* readability? maybe remove *) | Pexp_match _
        | Pexp_try _ | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
     } ->
@@ -132,10 +132,7 @@ let binary_expr_operand ~is_lhs expr =
     | {pexp_desc = Pexp_fun _}
       when ParsetreeViewer.is_underscore_apply_sugar expr ->
       Nothing
-    | {
-     pexp_desc =
-       Pexp_constraint _ | Pexp_fun _ | Pexp_function _ | Pexp_newtype _;
-    } ->
+    | {pexp_desc = Pexp_constraint _ | Pexp_fun _ | Pexp_newtype _} ->
       Parenthesized
     | _ when Ast_uncurried.expr_is_uncurried_fun expr -> Parenthesized
     | expr when ParsetreeViewer.is_binary_expression expr -> Parenthesized
@@ -228,8 +225,8 @@ let lazy_or_assert_or_await_expr_rhs ?(in_await = false) expr =
     | {
      pexp_desc =
        ( Pexp_lazy _ | Pexp_assert _ | Pexp_fun _ | Pexp_newtype _
-       | Pexp_function _ | Pexp_constraint _ | Pexp_setfield _ | Pexp_match _
-       | Pexp_try _ | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
+       | Pexp_constraint _ | Pexp_setfield _ | Pexp_match _ | Pexp_try _
+       | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
     } ->
       Parenthesized
     | _
@@ -276,9 +273,8 @@ let field_expr expr =
      pexp_desc =
        ( Pexp_lazy _ | Pexp_assert _
        | Pexp_extension _ (* %extension.x vs (%extension).x *) | Pexp_fun _
-       | Pexp_newtype _ | Pexp_function _ | Pexp_constraint _ | Pexp_setfield _
-       | Pexp_match _ | Pexp_try _ | Pexp_while _ | Pexp_for _
-       | Pexp_ifthenelse _ );
+       | Pexp_newtype _ | Pexp_constraint _ | Pexp_setfield _ | Pexp_match _
+       | Pexp_try _ | Pexp_while _ | Pexp_for _ | Pexp_ifthenelse _ );
     } ->
       Parenthesized
     | _ when ParsetreeViewer.has_await_attribute expr.pexp_attributes ->
diff --git a/compiler/syntax/src/res_printer.ml b/compiler/syntax/src/res_printer.ml
index a5fde5b0ae..383848802e 100644
--- a/compiler/syntax/src/res_printer.ml
+++ b/compiler/syntax/src/res_printer.ml
@@ -3394,8 +3394,6 @@ and print_expression ~state (e : Parsetree.expression) cmt_tbl =
           Doc.space;
           print_cases ~state cases cmt_tbl;
         ]
-    | Pexp_function cases ->
-      Doc.concat [Doc.text "x => switch x "; print_cases ~state cases cmt_tbl]
     | Pexp_coerce (expr, (), typ) ->
       let doc_expr = print_expression_with_comments ~state expr cmt_tbl in
       let doc_typ = print_typ_expr ~state typ cmt_tbl in