A monad for time-dependant values, providing explicit effects for delayed computations, latency, etc.


The Future(a, b) monad represents values that depend on time. This allows one to model time-based effects explicitly, such that one can have full knowledge of when they're dealing with delayed computations, latency, or anything that can not be computed immediately.

A common use for this monad is to replace the usual [Continuation-Passing Style][CPS] form of programming, in order to be able to compose and sequence time-dependent effects using the generic and powerful monadic operations.

var Future = require('monads.future')
function get(url) {
  return new Future(function(resolvereject) {
    var request = new XMLHttpRequest()
    request.onload = function() {
      if (!/2\d\d/.test(this.status))  reject(this.responseText)
      else                             resolve(this.responseText)
    }"get", url, true)
var t1 = get('/something')
var t2 = get('/other')
var t3 = {
             return a + b
t3.chain(function(a) {

The easiest way is to grab it from NPM. If you're running in a Browser environment, you can use [Browserify][]

$ npm install monads.future

If you're not using NPM, [Download the latest release][release], and require the monads.future.umd.js file:

var Future = require('monads.future')

[Download the latest release][release], and require the monads.future.umd.js file:

require(['monads.future'], function(Future) {
  ( ... )

[Download the latest release][release], and load the monads.future.umd.js file. The properties are exposed in the global Future object:

<script src="/path/to/monads.future.umd.js"></script>

If you want to compile this library from the source, you'll need [Git][], [Make][], [Node.js][], and run the following commands:

$ git clone git://
$ cd monads.future
$ npm install
$ make bundle

This will generate the dist/monads.future.umd.js file, which you can load in any JavaScript environment.

You can [read the documentation online][docs] or build it yourself:

$ git clone git://
$ cd monads.maybe
$ npm install
$ make documentation

Then open the file docs/literate/index.html in your browser.

This library assumes an ES5 environment, but can be easily supported in ES3 platforms by the use of shims. Just include [es5-shim][] :)

Copyright (c) 2013 Quildreen Motta.

Released under the MIT licence.

[Fantasy Land]: [Browserify]: [release]: [Git]: [Make]: [Node.js]: [es5-shim]: [docs]: [CPS]: