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Build Status NPM version Dependencies Status experimental

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 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(resolve, reject) {
    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

Using with CommonJS

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

var Future = require('monads.future')

Using with AMD

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

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

Using without modules

Download the latest 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>

Compiling from source

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 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.

Platform support

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.