mappable.js

import compose from "lodash/fp/compose";
import curry from "lodash/fp/curry";

const mappableWith = curry((compose, apply) => Object.assign(
    map => mappableWith(compose, compose(map, apply)),
    {valueOf: () => apply()}
));

const mappable = mappableWith(compose);

export {
  mappable as default,
  mappableWith
};

test.js

import mappable from './mappable';

const logAndReturn = (msg, value) => (console.log(msg, value), value);

const m1 = mappable(() => logAndReturn('m1', 10)); // no evaluation here

const m2 = m1(n => logAndReturn('m2', n / 2)); // no evaluation here

const m3 = m2(n => logAndReturn('m3', n * 5)); // no evaluation here

console.log('m1.valueOf()', m1.valueOf()); // we evaluate here (.valueOf)
// m1 10
// m1.valueOf() 10

console.log('m2.valueOf()', m2.valueOf()); // we evaluate here (.valueOf)
// m1 10
// m2 5
// m2.valueOf() 5

console.log('m3.valueOf()', m3.valueOf()); // we evaluate here (.valueOf)
// m1 10
// m2 5
// m3 25
// m2.valueOf() 25

// it can be used as a primitive due the implementation of valueOf
console.log(m1 + m2);
// m1 10
// m1 10
// m2 5
// 15