title: Return only the vowels in a list of strings
body: <p>I have to write the <code>onlyVowels :: [[Char]] -&gt; [[Char]]</code> function that should only return the vowels.</p>
  <p>For example: <code>onlyVowels [&quot;Return&quot;, &quot;Only&quot;, &quot;Vowels&quot;, &quot;Please&quot;] == [&quot;eu&quot;, &quot;Oy&quot;, &quot;oe&quot;, &quot;eae&quot;]</code></p>
  <p>So far, I have come up with this:</p>
  <pre><code>onlyVowels x = filter (isAVowel x) x where
    isAVowel x = elem x &quot;aeiouyAEIOUY&quot;
  </code></pre>
  <p>The problem with this is the fact that I have to check a list of words, not just a character. This exercise also prohibits the use of recursion.</p>