I have a reasonably complex predicate that’s giving me more solutions than expected - it is unexpectedly not deterministic. Is there a trick to debugging this kind of situation? For example, is it possible to set a breakpoint each time a new choicepoint is created? Thanks in advance, Stuart

Have you checked: Bug hunting toolbox

In general when you get too many answers is because you are missing an extra predicate in the conjunction. p(A) :- a(A), b(A). will produce (in general) more answers than: p(A) :- a(A), b(A), c(A). where c/1 restrains the conditions some more.

You can use setup_call_cleanup/3 to check for individual calls being deterministic, but it’s a cumbersome to do this – you could use the wrapping technique (using wrap_predicate/4) from library(rdet) to make this easier.

Thanks all. Here’s what I did. f(X):- % problem predicate. Unexpected multiple solutions. Replace with: f_(X):- % rename the problem predicate f(X):- f_(X), gtrace. ?- f(X). … and gtrace will continue at the problem choicepoint.

[image] swi: In general when you get too many answers is because you are missing an extra predicate in the conjunction. … at least in my case, it was because of an overlapping rule definition: %make_trees(Roots, Childre, Trees) make_trees([], [], [tree(nil,[])]). make_trees([], [tree(Data,Ch…

I struggled with the same problem. My solution was to wrap my “entry point” to the program in a setup-call-cleanup that throws if there is a choice point after the first success, and test very often during development so that I immediately notice any problems. The predicate itself: goal_is_det(Goa…

I guess you can also use leash/1 for the redo port only on the prediate you are debugging? I wish I had the time to properly document my experiences with debugging in particular, but sadly external circumstances usually force me to move faster than I would like :frowning:

rdet looks like a good solution.

As seen, there are a large number of ways to get more info. My personal solution is typically ?- gspy(suspect_pred). ?- go. As the debugger hits suspect_pred, use s (skip) to jump to the end and examine the choice points in the top-right window. You can click on these to see the source location…

Thank you for the good summary of the tools available to avoid dangling choice points. By “dangling choice point” I mean an unintentional, seemingly benign choice point that comes back some time later to bite you in the butt. [image] jan: If you have a predicate that is most of the time determ…

How to find unexpected choicepoints?

Help!

stuz5000 May 29, 2020, 9:02pm 15

Oh … similar thoughts here.

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How to find unexpected choicepoints?

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