issue-#57, #81 - Update 'takeWhile' impl. to return 'T[]'.

packages/fjl/src/list/takeWhile.ts

@@ -1,23 +1,22 @@
 import {TernaryPred} from "../types";
-import {instanceOf} from "../_platform";
 
 export const
 
   /**
    * Returns items upto point where predicate doesn't hold.
-   * For string type returns a string.
    */
-  takeWhile = <T>(pred: TernaryPred, xs: Iterable<T>): typeof xs | T[] => {
+  takeWhile = <T>(pred: TernaryPred, xs: Iterable<T>): T[] => {
     let i = 0;
     const out = [];
     for (const x of xs) {
       if (!pred(x, i, xs)) break;
       out.push(x);
       i += 1;
     }
-    return instanceOf(xs, String) ? out.join('') as typeof xs : out;
+    return out;
   },
 
   $takeWhile = <T>(pred: TernaryPred) =>
-    (xs: Iterable<T>): typeof xs | T[] =>
-      takeWhile(pred, xs);
+    (xs: Iterable<T>): T[] => takeWhile(pred, xs)
+
+;

packages/fjl/tests/list/test-takeWhile.ts

@@ -1,31 +1,37 @@
 import {
   alphabetArray,
-  alphabetString,
   isVowel,
-  nonAlphaNums,
   nonAlphaNumsArray,
   vowelsArray,
-  vowelsString
 } from "../helpers";
-import {range} from "../../src/list/range";
 import {takeWhile} from "../../src/list";
 
+const {stringify} = JSON;
+
 describe('#takeWhile', () => {
-  it('should take elements while predicate is fulfilled and vice-versa', () => {
-    (<[Parameters<typeof takeWhile>, ReturnType<typeof takeWhile>][]>[
-      [[isVowel, vowelsString], vowelsString],
-      [[isVowel, vowelsArray], vowelsArray],
-      [[isVowel, alphabetString], 'a'],
-      [[isVowel, alphabetArray], ['a']],
-      [[isVowel, range(0, 5)], []],
-      [[isVowel, nonAlphaNums], ''],
-      [[isVowel, nonAlphaNumsArray], []],
-      [[isVowel, ''], ''],
-      [[isVowel, []], []],
-    ])
-      .forEach(([args, expected]) => {
+  function* numRange() {
+    let i = 0;
+    while (i++ <= 5) {
+      yield i;
+    }
+  }
+
+  (<[Parameters<typeof takeWhile>, ReturnType<typeof takeWhile>][]>[
+    [[isVowel, vowelsArray], vowelsArray],
+    [[isVowel, alphabetArray], ['a']],
+    [[isVowel, numRange()], []],
+    [[isVowel, nonAlphaNumsArray], []],
+    [[isVowel, []], []],
+  ])
+    .forEach(([args, expected]) => {
+      it(`takeWhile(isVowel, ${stringify(args.slice(1))}) === ${stringify(expected)}`, () => {
         expect(takeWhile(args[0], args[1])).toEqual(expected);
       });
-  });
-  // @todo add failing case(s) here
+    });
+
+  [null, undefined, 0, {}].forEach(x =>
+    it(`should throw when: takeWhile(() => null, ${x + ''})`, () => {
+      expect(() => takeWhile(() => null, x as Iterable<any>)).toThrow()
+    })
+  );
 });