title: Modify all even values with a lens
body: <p>Suppose I have an array like this: <code>[1, 2, 3, 4]</code></p>
  
  <p>How would I modify only the even values using the lens package? I'm looking for something like:</p>
  
  <pre><code>filterLens even (+10) $ [1, 2, 3, 4]
  =&gt; [1, 12, 3, 14]
  </code></pre>