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ridgeworks / clpBNR

CLP(BNR) module for SWI-Prolog
MIT License
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Infinite loop and crash with write_term/2 #5

Closed JeanChristopheRohner closed 4 years ago

JeanChristopheRohner commented 4 years ago

Not sure if this is a bug or not but when i do ?- {X == 1.1}, write_term(X, [attributes(write)]). i get a massive printout and then a crash (mac OS X Catalina, SWI-Prolog version 8.2.1, clpBNR 0.9.0). /JC

ridgeworks commented 4 years ago

Currently, that's expected behaviour. The intervals in the constraint network reference each other via their attributes which contain a list of the constraints in which they're mentioned. That's how changes in one interval get propagated to others. But this results in an "indirect" cyclic structure, i.e., a graph, not a tree. attributes(write) just passes the attribute to recursively to write so it gets caught in an infinite loop which usually ends up in a crash (seg fault). portray is the recommended value (set as default by clpBNR) but obviously dots or ignore work as well.

Not too much I can do about it although it should probably be documented. And it's a bit tricky to check in write_term because the cycles are indirect through attributes rather than just variable unification (which is what cyclic_term/1 and acyclic_term/1 check for). It's all a bit unsanitary but do you think it's a big issue?

JeanChristopheRohner commented 4 years ago

Hi! "It's all a bit unsanitary but do you think it's a big issue?" No not at all, i just stumbled on it by accident and thought it might be useful to know (but you already did :-) ). Cheers/JC

ridgeworks commented 4 years ago

Thanks. I'll try to remember to document this somewhere.

ridgeworks commented 4 years ago

Just a heads up: I pushed a new version (0.9.2) to GitHub today. Nothing earth shattering, but a few enhancements (like print_interval), bug fixes (corner cases in couple of the primitives), and optimizations. Also some additional User Guide material and cleanups there (https://ridgeworks.github.io/clpBNR_pl/CLP_BNR_Guide/CLP_BNR_Guide.html) ; probably going to work on reference material next.

Any feedback welcome.