title: Filtering list of tuples
body: <p>New to Haskell and have a stumbling block. I'm trying to filter a list of tuples based on the first item.</p>
  
  <pre><code>filter (==(x,_)) lis
  </code></pre>
  
  <p>I get an illegal '_' error, but I'm not sure how I can get around it?</p>