Add flatMap to Belt.Array

Author: josh

jscomp/others/belt_Array.ml

@@ -267,6 +267,11 @@ let mapU a f =
 
 let map a f = mapU a (fun[@bs] a -> f a)
 
+let flatMapU a f =
+  concatMany (mapU a f)
+
+let flatMap a f = flatMapU a (fun[@bs] a -> f a)
+
 let getByU a p =
   let l = length a in
   let i = ref 0 in

jscomp/others/belt_Array.mli

@@ -395,6 +395,19 @@ val map: 'a array ->  ('a -> 'b ) -> 'b array
   ```
 *)
 
+val flatMapU: 'a array -> ('a -> 'b array [@bs]) -> 'b array
+val flatMap: 'a array -> ('a -> 'b array) -> 'b array
+(**
+  `flatMap xs f `
+
+  **return** a new array by calling `f` for each element of `xs` from
+  the beginning to end, and then concatenating the results
+
+  ```
+  flatMap [|1;2|] (fun x-> [|x + 10;x + 20|]) = [|11;21;12;22|]
+  ```
+*)
+
 val getByU: 'a array -> ('a -> bool [@bs]) -> 'a option
 val getBy: 'a array -> ('a -> bool) -> 'a option
 (**

lib/js/belt_Array.js

@@ -315,6 +315,14 @@ function map(a, f) {
   return mapU(a, Curry.__1(f));
 }
 
+function flatMapU(a, f) {
+  return concatMany(map(a, f));
+}
+
+function flatMap(a, f) {
+  return flatMapU(a, Curry.__1(f))
+}
+
 function getByU(a, p) {
   var l = a.length;
   var i = 0;
@@ -706,6 +714,8 @@ exports.forEachU = forEachU;
 exports.forEach = forEach;
 exports.mapU = mapU;
 exports.map = map;
+exports.flatMapU = flatMapU;
+exports.flatMap = flatMap;
 exports.getByU = getByU;
 exports.getBy = getBy;
 exports.getIndexByU = getIndexByU;