title: How to use a data type contains function
body: <p>I have following data type definition:</p>
  
  <pre><code>newtype Combine a b = 
    Combine { unCombine :: a -&gt; b }
  </code></pre>
  
  <p>and then I can defined as follow: </p>
  
  <pre><code>Prelude&gt; let f = Combine $ \n -&gt; Sum (n + 1)
  </code></pre>
  
  <p>My question is, how to use <code>f</code>?</p>