monads.validation

A disjunction (Either monad) that's more appropriate for validating inputs with better vocabulary & straight-forward failure aggregation.

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.

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(ab) { 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") 

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

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

var Validation = require('monads.validation')

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

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

[Download the latest release][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>

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.

You can [read the documentation online][docs] 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.

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]: https://github.com/fantasyland/fantasy-land [Browserify]: http://browserify.org/ [release]: https://github.com/folktale/monads.validation/releases/download/v0.2.0/monads.validation-0.2.0.tar.gz [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/monads.validation