title: What does :: (double colon) stand for?
body: <p>I see and use the <code>::</code> symbols <em>everywhere</em> but still don't know what the <code>::</code> symbol means when programming in Haskell, e.g.</p>
  
  <pre><code>run :: Int -&gt; Int -&gt; Int
  --  ??
  </code></pre>
  
  <p>What does <code>::</code> (double colon) stand for in Haskell?</p>