title: How to add spaces to string in Haskell
body: <p>I have a string <code>"AB0123456789"</code> and the output I would like to have is: <code>"AB01 2345 6789"</code> ... I want to add a space after every fourth character. How can I do this?</p>
  
  <pre><code>Main&gt; addSpace "AB0123456789"
  "AB01 2345 6789"
  </code></pre>