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folktale
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Data.Task

Build statusNPM versionDependencies statusLicenceStable API

The

Task(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 form of programming, in order to be able to compose and sequence time-dependent effects using the generic and powerful monadic operations.

Example

var Task = require('data.task')
var fs = require('fs')

// read : String -> Task(Error, Buffer) function read(path) { return new Task(function(reject, resolve) { fs.readFile(path, function(error, data) { if (error) reject(error) else resolve(data) }) }) }

// decode : Task(Error, Buffer) -> Task(Error, String) function decode(task) { return task.map(function(buffer) { return buffer.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 Task. var concatenated = intro.chain(function(a) { return outro.map(function(b) { return a + b }) })

// But the implementation of Task is pure, which means that you'll // never observe the effects by using chain or map or any other // method. The Task 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) } )

Installing

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

$ npm install data.task

Using with CommonJS

If you're not using NPM, Download the latest release, and require the

data.task.umd.js
file:
var Task = require('data.task')

Using with AMD

Download the latest release, and require the

data.task.umd.js
file:
require(['data.task'], function(Task) {
  ( ... )
})

Using without modules

Download the latest release, and load the

data.task.umd.js
file. The properties are exposed in the global
Task
object:

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://github.com/folktale/data.task.git
$ cd data.task
$ npm install
$ make bundle

This will generate the

dist/data.task.umd.js
file, which you can load in any JavaScript environment.

Documentation

You can read the documentation online or build it yourself:

$ git clone git://github.com/folktale/data.task.git
$ cd data.task
$ npm install
$ make documentation

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 :)

Licence

Copyright (c) 2013-2015 Quildreen Motta.

Released under the MIT licence.

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