title: Solve S-expression with binary search tree
body: <p>I have a string that gets parsed into a reader which puts it into an array as shown:</p>
  
  <pre><code>X = '(mul 5 (add 5 5))'
  Y = parser(X)
  y = ['mul', 5, ['add', 5, 5]]
  </code></pre>
  
  <p>I want to find the value of this expression <code>Y</code>. It has been suggested that I use a binary search tree and to traverse through the nodes. I just don't know how to do this. Note, I need this to work as a general routine, so that it will work for any string such as <code>'(mul (add 1 2) (log 8))</code></p>