fix(array): fix up A.takeWhile implementation

__tests__/Array/dropWhile.test.ts

@@ -13,8 +13,8 @@ describe('dropWhile', () => {
   })
 
   it('drops elements from the beginning of the array until an element is reached which does not satisfy the given predicate', () => {
-    const result = A.dropWhile(xs, x => x < 4)
-    expect(result).toEqual([4, 5, 6, 7])
+    expect(A.dropWhile(xs, x => x < 4)).toEqual([4, 5, 6, 7])
+    expect(A.dropWhile([1, 3, 5, 7, 9], x => x < 5)).toEqual([5, 7, 9])
   })
 
   it('returns correct array elements if either true or false', () => {

__tests__/Array/takeWhile.test.ts

@@ -5,8 +5,8 @@ const xs = [1, 2, 3, 4, 5, 6, 7]
 // TODO: expectType
 describe('takeWhile', () => {
   it('returns a new array, filled with elements from the provided array until an element does not pass the provided predicate', () => {
-    const result = A.takeWhile(xs, x => x < 4)
-    expect(result).toEqual([1, 2, 3])
+    expect(A.takeWhile(xs, x => x < 4)).toEqual([1, 2, 3])
+    expect(A.takeWhile([3, 5, 3], x => x < 4)).toEqual([3])
   })
 
   it('returns correct array elements if either true or false', () => {

src/Array/Array.res

@@ -172,13 +172,24 @@ let takeExactly = (xs, n) =>
   "Returns a new array, filled with elements from the provided array until an element doesn't pass the provided predicate."
 )
 @gentype
-let takeWhile = (xs, predicateFn) =>
-  Belt.Array.reduceU(xs, [], (. acc, element) => {
-    if predicateFn(element) {
-      Js.Array2.push(acc, element)->ignore
+let takeWhile = (xs, predicateFn) => {
+  let index = ref(0)
+  let break = ref(false)
+  let arr = []
+
+  while index.contents < length(xs) && !break.contents {
+    let value = Belt.Array.getUnsafe(xs, index.contents)
+
+    if predicateFn(value) {
+      Js.Array2.push(arr, value)->ignore
+      index := succ(index.contents)
+    } else {
+      break := true
     }
-    acc
-  })
+  }
+
+  arr
+}
 
 %comment(
   "Returns a new array that does not contain the first `n` elements of the provided array, or an empty array if `n` is either less than `0` or greater than the length of the provided array."