Memoized Y Combinator

memoized_y_combinator.js

const M = f => f(f);

const Y = fn => M(
  maker => x => fn(maker(maker))(x)
);

const YY = fn => {
  const cache = new Map;

  return M(
    maker => x => {
      if (!cache.has(x)) {
        cache.set(x, fn(maker(maker))(x));
      }

      return cache.get(x);
    }
  );
};

const mFact = YY(
  self => n => {
    console.log(n);

    if (n === 0) return 1;

    return n * self(n - 1);
  }
);