title: What causes this for loop to print a series of nil?
body: <p>Can anyone explain what causes all the nil values in the following?</p>
  
  <pre><code>(defn my-for []
     (for [n (range 0 40)]
       (println n)))
  (my-for)
  </code></pre>
  
  <p>Result (omitting some numerical values):</p>
  
  <p>(0
  1
  2
  ...
  30
  31
  nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil nil 32
  33
  ...
  38
  39
  nil nil nil nil nil nil nil nil nil)</p>