Eager Continuation in JavaScript

continuation.js

const {tagged} = require('daggy');

let Continuation = tagged('x');

Continuation.prototype.of = Continuation.of = x => {
  return new Continuation((resolve) => resolve(x));
}

Continuation.prototype.chain = function(f) {
  return this.x(f);
};

Continuation.prototype.inspect = function() {
  return `Continuation(${this.x})`;
}

// derivations
Continuation.prototype.map = function(f) {
  var m = this;
  return m.chain(a => m.of(f(a)));
}

Continuation.prototype.ap = function(m) {
  return this.chain(f => m.map(f));
}

module.exports = Continuation;

examples.js

const Cont = require('../lib/continuation');

// pointed version
const c = Cont.of(5) // initial value
  .chain((x) => {
    return Cont.of(x + 5); // synchronous computation
  })
  .chain((x) => { // async computation
    return new Cont((resolve) => {
      setTimeout(() => resolve(x + 15), 500);
    });
  });

Cont.of(console.log).ap(c);

👍 https://github.com/fantasyland/fantasy-promises/blob/master/src/promise.js#L19

This is how fantasy-promises are implemented :)