title: How can I sum the key value of a list of records?
body: <p>For example:</p>
  
  <pre><code>{defrecord Item [cost value]}
  {def items [(Item. 20 50)
              (Item. 30 40)
              (Item. 10 70)]
  </code></pre>
  
  <p>How would I go about summing the cost of items? (so I'd get 60)</p>