Monads: Validation

The Validation(a, b) is a disjunction that's more appropriate for validating inputs, or any use case where you want to aggregate failures. Not only the Validation monad provides a better terminology for working with such cases (Failure and Success versus Left and Right), it also allows one to easily aggregate failures and successes as an Applicative Functor.

Example

var Validation = require('monads.validation')
var Success = Validation.Success
var Failure = Validation.Failure

function isPasswordLongEnough(a) {
  return a.length > 6?    Success(a)
  :      /* otherwise */  Failure("Password must have more than 6 characters")
}

function isPasswordStrongEnough(a) {
  return /[\W]/.test(a)?  Success(a)
  :      /* otherwise */  Failure("Password must contain special characters")
}

function isPasswordValid(a) {
  return [isPasswordLongEnough(a), isPasswordStrongEnough(a)]
           .map(function(x){ return x.bimap(liftNel, k) })
           .reduce(function(a, b) { return a.ap(b) })
}

function liftNel(a) {
  return [a]
}

function k(a){ return function(b) {
  return a
}}

isPasswordValid("foo")
// => Validation.Failure([
//      "Password must have more than 6 characters.",
//      "Password must contain special characters."
//    ])

isPasswordValid("rosesarered")
// => Validation.Failure([
//      "Password must contain special characters."
//    ])

isPasswordValid("rosesarered$andstuff")
// => Validation.Success("rosesarered$andstuff")

Installing

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

$ npm install monads.validation

Using with CommonJS

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

var Validation = require('monads.validation')

Using with AMD

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

require(['monads.validation'], function(Validation) {
  ( ... )
})

Using without modules

Download the latest release, and load the monads.validation.umd.js file. The properties are exposed in the global folktale.monads.Validation object:

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

This will generate the dist/monads.validation.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/monads.validation.git
$ cd monads.validation
$ 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 :)

Licence

Copyright (c) 2013 Quildreen Motta.

Released under the MIT licence.