The documentation for 'if' is here <a href="http://docs.racket-lang.org/reference/if.html?q=if">http://docs.racket-lang.org/reference/if.html?q=if</a> Here's a slightly modified example from the doc using 'if': (if (positive? -5) (error "shouldn't get here") (display "hi")) You might want to consider the 'when', documented here <a href="http://docs.racket-lang.org/reference/when_unless.html?q=when">http://docs.racket-lang.org/reference/when_unless.html?q=when</a> And here's an example from the doc using 'when': (when (positive? -5) (display "hi")) Cheers, Kieron.