Understand how lift works on function level

ramdaLift.js

As I have hard time understanding the same issue, I decided to take a peek from Ramda's source code. Will write a blogpost about `this`. Meanwhile—I made a commented gist how Ramda's `lift` work step by step.

from: https://gist.github.com/philipyoungg/a0ab1efff1a9a4e486802a8fb0145d9e

    // Let's make an example function that takes an object and return itself.
    // 1. Ramda's lift level
    lift(zipObj)(keys, values)({a: 1}) // returns {a: 1}

    // this is how lift works in the background
    module.exports = _curry2(function liftN(arity, fn) {
      var lifted = curryN(arity, fn);
      return curryN(arity, function() {
        return _reduce(ap, map(lifted, arguments[0]), Array.prototype.slice.call(arguments, 1)); // found it. let's convert no 1 to no 2
      });
    });

    // 2. Ramda's reduce level
    reduce(ap, map(zipObj, keys))([values])

    // This time, I'm taking reduce implementation that is not from Ramda (because honestly I can't understand it) but it should work similarly.
    // credits to carlsednaoui => https://gist.github.com/carlsednaoui/5959036

    Array.prototype.reduce = function(fn, acc) {
      if (acc === undefined && this.length !== 0)
        return this.slice(1).reduce(fn, this[0]);

      if (this.length === 0) return acc;

      return this.slice(1).reduce(fn, fn(acc, this[0]));
    };

    // 3. Ramda's ap level
    ap(map(zipObj, keys), values)

    // how ap works in the background
    module.exports = _curry2(function ap(applicative, fn) {
      return (
        typeof applicative.ap === 'function' ?
          applicative.ap(fn) :
        typeof applicative === 'function' ? // 
          function(x) { return applicative(x)(fn(x)); } : // because the first argument is a function, ap return this.
        // else
          _reduce(function(acc, f) { return _concat(acc, map(f, fn)); }, [], applicative)
      );
    });

    // 4. Voilà. Here's the final result.
    map(zipObj, keys)({a: 1})(values({a: 1}))

    // Hope it helps you and everyone else!