refactor(array): bind to flatMap instead of reimplementing it

Author: glennsl

src/Core__Array.mjs

@@ -3,7 +3,6 @@
 import * as Curry from "rescript/lib/es6/curry.js";
 import * as Js_math from "rescript/lib/es6/js_math.js";
 import * as Caml_option from "rescript/lib/es6/caml_option.js";
-import * as Caml_splice_call from "rescript/lib/es6/caml_splice_call.js";
 
 function make(len, x) {
   if (len <= 0) {
@@ -136,10 +135,6 @@ function keepSome(__x) {
               }));
 }
 
-function flatMap(a, f) {
-  return Caml_splice_call.spliceObjApply([], "concat", [a.map(f)]);
-}
-
 function findMap(arr, f) {
   var _i = 0;
   while(true) {
@@ -171,7 +166,6 @@ export {
   keepSome ,
   shuffle ,
   shuffleInPlace ,
-  flatMap ,
   findMap ,
 }
 /* No side effect */

src/Core__Array.res

@@ -224,8 +224,7 @@ let filterMap = (a, f) => filterMapU(a, (. a) => f(a))
 
 let keepSome = filterMap(_, x => x)
 
-// TODO: Change this implementation?
-let flatMap = (a, f) => []->concatMany(map(a, f))
+@send external flatMap: (array<'a>, 'a => array<'b>) => array<'b> = "flatMap"
 
 let findMap = (arr, f) => {
   let rec loop = i =>

src/Core__Array.resi

@@ -106,7 +106,7 @@ let filterMap: (array<'a>, 'a => option<'b>) => array<'b>
 let keepSome: array<option<'a>> => array<'a>
 let shuffle: array<'a> => array<'a>
 let shuffleInPlace: array<'a> => unit
-let flatMap: (array<'a>, 'a => array<'b>) => array<'b>
+@send external flatMap: (array<'a>, 'a => array<'b>) => array<'b> = "flatMap"
 let findMap: (array<'a>, 'a => option<'b>) => option<'b>
 
 /**