title: How to return the next letter in the alphabet of given letter wrapped around in Haskell
body: <p>I'm trying to implement a function that returns the next letter in alphabetical order. For example:</p>
  
  <pre><code>&gt; returnNext 'A'
    'B'
  </code></pre>
  
  <p>But also:</p>
  
  <pre><code>&gt; returnNext 'Z'
    'A'
  </code></pre>
  
  <p>The function should thus cycle between char codes in alphabetical order (mod 26).</p>