title: Why Symbol in clojure can be used as Functions?
body: <p>I refer you to this short code:</p>
  
  <pre><code>('a 1)
  ;==&gt; nil
  ('a 1 2)
  ;=&gt;2
  </code></pre>
  
  <p>why can the symbol <code>a</code> be used as a function in this context?</p>