Default values for function arguments are computed once when the function is defined, not each time the function is called. You'll want to make the defaults all false and get the parameter values inside the function body.
-- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.