title: Can you return nothing from a function in Scheme?
body: <p>I'm writing a scheme interpreter, and in the case of an if statement such as:</p>
  
  <pre><code>(if (&lt; 1 0) 'true)
  </code></pre>
  
  <p>Any interpreter I've tried just returns a new prompt. But when I coded this, I had an if for whether there was an alternative expression. What can I return in the if such that nothing gets printed?</p>
  
  <pre><code>(if (has-alternative if-expr)
    (eval (alternative if-expr))
    #f) ;; what do I return here?
  </code></pre>