title: How to sum over same indices of list of lists?
body: <p>How can I sum a list of lists where all the values at the a index?</p>
  <p>For example:</p>
  <pre><code>let k = [ [1,1,1], [2,2,2], [3,3,3] ]
  sumFoo k
  &gt; [ 6, 6, 6]
  </code></pre>
  <hr />
  <p>I know that I can sum two lists as:</p>
  <pre><code>zipWith (+) [1,2,3] [2,3,4]
  </code></pre>
  <p>But what about a list of list? I tried something like:</p>
  <pre><code>foldr (\xs ys -&gt; zipWith (+) xs ys) [] k
  </code></pre>
  <p>but that gives me an empty list!</p>