Data.Validation
===============

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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` 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

```js
var Validation = require('data.validation')
var Success = Validation.Success
var Failure = Validation.Failure

// Functions that need to do validation return one of two cases:
//
//  -  A Success with the value they want to propagate.
//  -  Some value representing one or more failures, using a semigroup.
//     Lists are the more straight-forward semigroup, so we just use them
//     here.
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"])
}

// To aggregate the failures, we start with a Success case containing
// a curried function of arity N (where N is the number of validations),
// and we just use an `.ap`-ply chain to get either the value our Success
// function ultimately returns, or the aggregated failures.
function isPasswordValid(a) {
  return Success(function(x){ return function(y){ return a }})
           .ap(isPasswordLongEnough(a))
           .ap(isPasswordStrongEnough(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 data.validation


### Using with CommonJS

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

```js
var Validation = require('data.validation')
```


### Using with AMD

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

```js
require(['data.validation'], function(Validation) {
  ( ... )
})
```


### Using without modules

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

```html
<script src="/path/to/data.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/data.validation.git
    $ cd data.validation
    $ npm install
    $ make bundle
    
This will generate the `dist/data.validation.umd.js` file, which you can load in
any JavaScript environment.

    
## Documentation

You can [read the documentation online][docs] or build it yourself:

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

Then open the file `docs/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](https://github.com/folktale/data.validation/blob/master/LICENCE).

<!-- links -->
[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.validation
<!-- [release: https://github.com/folktale/data.validation/releases/download/v$VERSION/data.validation-$VERSION.tar.gz] -->
[release]: https://github.com/folktale/data.validation/releases/download/v1.3.0/data.validation-1.3.0.tar.gz
<!-- [/release] -->