<section class="intro">

<h2>PureScript is a small strongly typed programming language that compiles to JavaScript.</h2>

<div class="link">

<a href="http://try.purescript.org/">Try It!</a>

</div>

</section>

<section class="example">

<h3>Examples</h3>

<div class="current example">

<h4>Modifying the DOM</h4>

<p>PureScript’s expressive type system and lightweight syntax make it simple to define <a href="https://leanpub.com/purescript/read#leanpub-auto-domain-specific-languages">domain-specific languages</a>, which can be used to solve problems like templating the DOM. Bindings also exist for libraries such as React and Angular.js.</p>

<pre>

<span class="kr">import</span> <span class="nn">Flare</span>

<span class="kr">import</span> <span class="nn">Flare.Smolder</span>

&nbsp;

<span class="nf">ui</span> :: UI _ H.Markup

<span class="nf">ui</span> = greet <span class="kt">&lt;$&gt;</span> string <span class="s">"Name"</span> <span class="s">"World"</span>

where

<span class="nf">greet</span> name = h1 <span class="kt">$</span> text <span class="kt">$</span> <span class="s">"Hello, "</span> <span class="kt">&lt;&gt;</span> name <span class="kt">&lt;&gt;</span> <span class="s">"!"</span></pre>

</div>

<div class="example">

<h4>HTML5 Canvas</h4>

<p>Higher-order functions allow the developer to write fluent, expressive code. Here, higher-order functions are being used to capture some common patterns when <a href="https://leanpub.com/purescript/read#leanpub-auto-canvas-graphics">working with HTML5 canvas</a>, such as closing and filling paths.</p>

<pre>

<span class="kr">import</span> <span class="nn">Control.Apply</span>

<span class="kr">import</span> <span class="nn">Graphics.Canvas.Free</span>

<span class="nf">scene</span> =

filled $ closed <span class="kr">do</span>

moveTo <span class="mi">0</span> <span class="mi">0</span>

lineTo <span class="mi">50</span> <span class="mi">0</span>

lineTo <span class="mi">25</span> <span class="mi">50</span>

<span class="kr">where</span>

<span class="nf">closed</span> path = beginPath *&gt; path &lt;* closePath

<span class="nf">filled</span> shape = shape &lt;* fill</pre>

</div>

<div class="example">

<h4>Callback Hell</h4>

<p>The problem of <a href="https://leanpub.com/purescript/read#leanpub-auto-callback-hell">callback hell</a> can be solved by using PureScript’s type system to capture complex control flow as functions in a safe way. Here, the continuation monad is used to hide the boilerplate code associated with handling callbacks.</p>

<pre>

<span class="kr">import</span> <span class="nn">Control.Monad.Aff</span>

<span class="kr">import</span> <span class="nn">Control.Monad.Aff.Par</span>

<span class="kr">data</span> <span class="kt">Model</span> = <span class="kt">Model</span> (<span class="kt">List Product</span>)

<span class="nf">loadModel</span> = <span class="kr">do</span>

popular <- get <span class="s">"/products/popular"</span>

products <- runPar $ for_ popular \product -> <span class="kt">Par</span> (get product.uri)

return $ <span class="kt">Model</span> products</pre>

</div>

<div class="example">

<h4>Generative Testing</h4>

<p>PureScript provides a form of ad-hoc polymorphism in the form of type classes, inspired by Haskell. Type classes are used in the QuickCheck and StrongCheck libraries to support <a href="https://leanpub.com/purescript/read#leanpub-auto-generative-testing">generative testing</a>, which separates test definitions from the generation of test cases.</p>

<pre>

<span class="kr">import</span> <span class="nn">Test.QuickCheck</span>

<span class="nf">main</span> = <span class="kr">do</span>

quickCheck $ <span class="nf">\</span>xs ys -&gt;

isSorted $ merge (sort xs) (sort ys)

quickCheck $ <span class="nf">\</span>xs ys -&gt;

xs `isSubarrayOf` merge xs ys</pre>

</div>

</section>

<section class="features">

<h3>Features</h3>

<ul>

<li>Algebraic data types</li>

<li>Pattern matching</li>

<li>Type inference</li>

<li>Type classes</li>

<li>Higher kinded types</li>

<li>Rank-N types</li>

<li>Extensible records</li>

<li>Extensible effects</li>

<li>Modules</li>

<li>Simple FFI</li>

<li>No runtime system</li>

<li>Human-readable output</li>

</ul>

</section>