data.future

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

Data.Future

The Future(a, b) structure 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('data.future')
var fs = require('fs')
 
// read : String -> Future(Error, Buffer) 
function read(path) {
  return new Future(function(rejectresolve) {
    fs.readFile(path, function(errordata) {
      if (error)  reject(error)
      else        resolve(data)
    })
  })
}
 
// decode : Future(Error, Buffer) -> Future(Error, String) 
function decode(buffer) {
  return buffer.map(function(a) {
    return a.toString('utf-8')
  })
}
 
var intro = decode(read('intro.txt'))
var outro = decode(read('outro.txt'))
 
// You can use `.chain` to sequence two asynchronous actions, and 
// `.map` to perform a synchronous computation with the eventual 
// value of the Future. 
var concatenated = intro.chain(function(a) {
                     return outro.map(function(b) {
                       return a + b
                     })
                   })
 
// But the implementation of Future is pure, which means that you'll 
// never observe the effects by using `chain` or `map` or any other 
// method. The Future just records the sequence of actions that you 
// wish to observe, and defers the playing of that sequence of actions 
// for your application's entry-point to call. 
// 
// To observe the effects, you have to call the `fork` method, which 
// takes a callback for the rejection, and a callback for the success. 
concatenated.fork(
  function(error) { throw error }
, function(data)  { console.log(data) }
)

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

$ npm install data.future

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

var Future = require('data.future')

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

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

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

<script src="/path/to/data.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://github.com/folktale/data.future.git
$ cd data.future
$ npm install
$ make bundle

This will generate the dist/data.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://github.com/folktale/monads.maybe.git
$ cd monads.maybe
$ npm install
$ make documentation

Then open the file docs/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) 2013-2014 Quildreen Motta.

Released under the MIT licence.

[Fantasy Land]: https://github.com/fantasyland/fantasy-land [Browserify]: http://browserify.org/ [Git]: http://git-scm.com/ [Make]: http://www.gnu.org/software/make/ [Node.js]: http://nodejs.org/ [es5-shim]: https://github.com/kriskowal/es5-shim [docs]: http://folktale.github.io/data.future [CPS]: http://matt.might.net/articles/by-example-continuation-passing-style/ [release]: https://github.com/folktale/data.future/releases/download/v2.3.0/data.future-2.3.0.tar.gz