Tracing and trace/2

What would be really useful would be something like this:

?- my_caller(an_arg)
false.    % Now Sherlock Holmes has to do the work
?- trace_children(my_caller,+fail). 
?- my_caller(an_arg).
T Fail: my_callee(some_arg)    % Wouldn't this be great? we know where it failed and the args.

I bet we all in this forum have gotten false for an answer and then we have to start digging around :grin:

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If there are semidet predicates, tracing to fail ports is going to generate a lot of noise. It would be nice to have Prolog validate the det/semidet/etc. notations as part of the debug process. (I mostly use library(rdet), but it lacks support for ensuring no choice points, and I haven’t got around to adding such support.)

You’re right, didn’t think about the noise with multi and semidet preds. What if trace_children/[2,3] by default prints only the last <n> failures (perhaps 3 is a good number) before returning to the top-level? This would eliminate the noise and most likely point to the culprit. What do you think?