title: Built-in factorial function in Haskell
body: <p>I know this sounds like a stupid question, but here it is: Is there a built-in factorial in Haskell?</p>
  
  <p>Google gives me tutorials about Haskell explaining how I can implement it myself, and I could not find anything on Hoogle. I don't want to rewrite it each time I need it.</p>
  
  <p>I can use <code>product [1..n]</code> as a replacement, but is there a true <code>Int -&gt; Int</code> factorial built-in function?</p>