title: Assigning variables (variable mutation) in racket
body: <p>I have the following function that given an expression, executes it :</p>
  
  <pre><code>(define (foo exp0) exp0)
  </code></pre>
  
  <p>If I do the following:</p>
  
  <pre><code>(define x 5)
  (foo (+ x 4))
  (foo (* x 2))
  display(x)
  </code></pre>
  
  <p>I would like for display(x) to display 18. Basically, how can I assign the value of the given expression back to the given variable? </p>