fix(hof): Rewrite curry from scratch

Fixes #350

Author: christopherthielen

src/common/hof.ts

@@ -45,22 +45,17 @@ import { Predicate } from './common';
  *
  * ```
  *
- * Stolen from: http://stackoverflow.com/questions/4394747/javascript-curry-function
- *
  * @param fn
  * @returns {*|function(): (*|any)}
  */
 export function curry(fn: Function): Function {
-  const initial_args = [].slice.apply(arguments, [1]);
-  const func_args_length = fn.length;
-
-  function curried(args: any[]) {
-    if (args.length >= func_args_length) return fn.apply(null, args);
-    return function() {
-      return curried(args.concat([].slice.apply(arguments)));
-    };
-  }
-  return curried(initial_args);
+  return function curried() {
+    if (arguments.length >= fn.length) {
+      return fn.apply(this, arguments);
+    }
+    const args = Array.prototype.slice.call(arguments);
+    return curried.bind(this, ...args);
+  };
 }
 
 /**

test/hofSpec.ts

@@ -0,0 +1,59 @@
+import { curry } from '../src/common';
+
+describe('curry', () => {
+  let original: jasmine.Spy;
+  beforeEach(() => {
+    original = jasmine.createSpy('original', function(a, b, c) {});
+  });
+
+  it('should accept a function and return a new function', () => {
+    expect(typeof curry(original)).toBe('function');
+  });
+
+  it('should return a function that invokes original only when all arguments are supplied', () => {
+    const curried1 = curry(original);
+    curried1(1, 2, 3);
+    expect(original).toHaveBeenCalledTimes(1);
+    expect(original).toHaveBeenCalledWith(1, 2, 3);
+  });
+
+  it('should pass extra arguments through to original function', () => {
+    const curried1 = curry(original);
+    curried1(1, 2, 3, 4);
+    expect(original).toHaveBeenCalledTimes(1);
+    expect(original).toHaveBeenCalledWith(1, 2, 3, 4);
+  });
+
+  it('should keep returning functions that return functions if no arguments are supplied', () => {
+    const curried1 = curry(original);
+    expect(typeof curried1).toBe('function');
+
+    const curried2 = curried1();
+    expect(typeof curried2).toBe('function');
+
+    const curried3 = curried2();
+    expect(typeof curried3).toBe('function');
+
+    const curried4 = curried3();
+    expect(typeof curried4).toBe('function');
+
+    const curried5 = curried4();
+    expect(typeof curried5).toBe('function');
+
+    const curried6 = curried5();
+    expect(typeof curried6).toBe('function');
+
+    expect(original).toHaveBeenCalledTimes(0);
+  });
+
+  it('should keep returning functions that return functions until all arguments are supplied', () => {
+    const curried1 = curry(original);
+    const curried2 = curried1(1);
+    const curried3 = curried2(2);
+    const result = curried3(3);
+
+    expect(result).toBeUndefined();
+    expect(original).toHaveBeenCalledTimes(1);
+    expect(original).toHaveBeenCalledWith(1, 2, 3);
+  });
+});