Functional Helpers (In ES6 Syntax)

functional.js

const map = f => step => (a, c) => step(a, f(c));

const filter = predicate => step => (a, c) => predicate(c) ? step(a, c) : a;

const compose = (...fns) => x => fns.reduceRight((y, f) => f(y), x);

const curry = (f, arr = []) => (...args) => (
  a => a.length === f.length ? f(...a) : curry(f, a)
)([...arr, ...args]);

const transduce = curry((step, initial, xform, foldable) =>
  foldable.reduce(xform(step), initial)
);

const concatArray = (a, c) => a.concat([c]);

const toArray = transduce(concatArray, []);

const logStep = v => { console.log(v); return v; }