Well, I see two things going on here. First, this example is an interesting one, because there’s no stack trace to display; the (/ 1 n) is the only “frame” left on the “stack”, because the call to sub2 has already returned, and the body of “reciprocal” is in tail position with respect to the call. If you add a “(+ 1 …)” around the reciprocal call, then there’s a stack to display…
…except that you still won’t see an arrow in BSL, because that’s a #lang racket thing. That is: if you change the language to “Use language defined in source”, and insert #lang racket at the beginning, and add a (+ 1 …) around the reciprocal, and run the program, you’ll see an arrow from the (/ 1 n) to the (+ 1 …) context as I believe you expected. I think the pedagogically correct answer here is that the arrows that you see in racket aren’t really the “right thing” for an educational setting. Instead, I think I might suggest using the stepper, instead. (Me? Biased?) In this case, I think I would jump to the end of the evaluation, and then step backward to see where the error came from. I also think that there’s probably value in the “tree-cer” approach that Krishnamurthi et al. have been working on[*] for Pyret, which shows the evaluation of a term as a single large tree, allowing you to inspect each call and the arguments that were passed to each call. John [*] I thought of it independently, but they thought of it first, and actually implemented it. :) > On May 2, 2019, at 4:02 PM, Mark Engelberg <mark.engelb...@gmail.com> wrote: > > Working with a student in DrRacket for the first time in a while. > > I notice that in BSL, an error in a function does not tell you what input to > the function caused the error, nor does it show the stack trace by drawing > arrows in the definitions window the way I remember. > > When did this behavior change? Is there a way to turn on better error > reporting and stack traces? > > Example: > > (define (reciprocal n) > (/ 1 n)) > > (define (sub2 n) > (- n 2)) > > (define a (reciprocal (sub2 2))) > > > > -- > 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. -- 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.
