Fix applicative functor

Author: tshemsedinov

JavaScript/5-proto-ap.js

@@ -5,18 +5,19 @@ function Maybe(x) {
 }
 
 Maybe.prototype.map = function(fn) {
-  return (this.x && fn) ? fn(this.x) : null;
+  const res = (this.x && fn) ? fn(this.x) : null;
+  return res instanceof Maybe ? res : new Maybe(res);
 };
 
-Maybe.prototype.ap = function(maybe) {
-  return new Maybe(this.map(mbValue => (maybe.map(
-    mbFunction => mbFunction(mbValue)
-  ))));
+Maybe.prototype.ap = function(functor) {
+  return this.map(val => functor.map(f => f(val)));
 };
 
 // Usage
 
 const a = new Maybe(5);
 const f1 = new Maybe(x => x * 2);
 const f2 = new Maybe(x => ++x);
+
 a.ap(f1).ap(f2).map(console.log);
+