Funtion as Applicative in JavaScript

ap.js

let _ = require('lodash');


let pure = x => _ => x;

let ap = f => g => x => f(x)(g(x));

let add = a => b => a + b;
let multi = a => b => a * b;
let minus3 = a => b => c => a - b - c;

// (+) <*> (2*) $ 3 :---> (+ 3 (* 2 3)) = 9
console.log(ap(add)(multi(2))(3)); // 9

// minus3 <*> (2+) <*> (3*) $ 5 :---> 5 - (2+5) - (3*5) = -17
console.log(ap(ap(minus3)(add(2)))(multi(3))(5)); // = -17

// 为了使用现有工具演示，以下两个函数的 f 暂时不克里化
let zipWith = f => xs => ys => _.zipWith(xs, ys, f);
let map = f => xs => xs.map(f);

// zipWith (*) <*> map (2+) $ [1,2,3] :--->  zipWith (*) [1,2,3] (map (2+) [1,2,3]) = [3,8,15]
console.log(ap(zipWith((a,b) => a*b))(map(a => 2+a))([1,2,3])); // [3,8,15]