title: In Clojure how to choose a value if nil
body: <p>In Clojure what is the idiomatic way to test for nil and if something is nil then to substitute a value? </p>
  
  <p>For example I do this a lot:</p>
  
  <pre><code> let [ val    (if input-argument input-argument "use default argument")]
  </code></pre>
  
  <p>: but I find it repetitive having to use "input-argument" twice.</p>