Is there any convenient way to print the return value of a procedure in Racket? For example, (define (test exp) (match exp [(...) some-value-1] [(...) some-value-2] [(...) some-value-3])) What I want to do is to embed some debugging printf in the test, something like: (define (test exp) (begin0 (match exp [(...) some-value-1] [(...) some-value-2] [(...) some-value-3]) (printf "test return ~v\n" *last-value*) ; <-- *last-value* needed )) Current workaround is using let , but not convenient: (define (test exp) ((let ((result (match exp [(...) some-value-1] [(...) some-value-2] [(...) some-value-3]))) (printf "test return ~v\n" result) result))) Thanks.

https://docs.racket-lang.org/mischief/debug__Explicit_Debugging.html?q=debug

I never knew about (require debug). I never wrote code that didn’t have bugs. Now that I have been given an umbrella, perhaps the rain will stop.

@samth I just installed mischief. Do you mean to define the test procedure by define/debug? It works, thanks. Although it will print many wordy log messages and slow…

You can also write (debug test e) if you care about a particular call-site.

But, printing lots of log messages is precisely what you’re asking for.

@samth It’s useful, thanks.

BTW, It would be nice, if some log messages could be reduced. For example, from #;>> function: #;>> contract #;>> [e:\......\xxxxxx.rkt:9.15] #; ! Argument redex: '(redex (* (* 1 2) (* 3 (* 4 0)))) #; ! Result: '(* 1 (* 2 (* 3 (* 4 0)))) to #;>> function: contract #; ! Argument redex: '(redex (* (* 1 2) (* 3 (* 4 0)))) #; ! Result: '(* 1 (* 2 (* 3 (* 4 0)))) I have tagged the conract procedure by define/debug, so there is no need to tell me where this file is.

once i set a label on a message% as for example a string can i not set it to a bitmap% ?

Yes, that’s correct

If you think mischief is too heavy, you can use https://docs.racket-lang.org/debug/ instead

Just insert #R in front of (match ..., and you will be able to trace the value produced by the expression.