[Edit to add examples] I’m trying to table a predicate of specializations (like a class hierarchy) where the order of backtracking matters: :- table specializesAll/2. specializesAll(Type, BaseType) :- rel(Type, specializes, BaseType). specializesAll(Type, BaseType) :- rel(IntermediateType…

[image] ericzinda: Is this by design Good question :slight_smile: As is, answers are returned in more or less arbitrary order from a trie that uses a hash table for non-deterministic nodes. Sure, we could preserve order (at some cost). Note that predicates that need tabling (as otherwise…

[edit: fixed typo] OK, thanks @jan (and thanks for the tip!). I’ve been working around it with an approach like this. It still gives me some great performance gains: specializesAll(Type, BaseType) :- specializesAllSet(Type, BaseType, Set), member([Type, BaseType], Set). :- table specialize…

Considering you table /2 and define /3, this seems unlikely :slight_smile: I guess this is a typo?

[image] jan: I guess this is a typo? Yep! Fixed.

[image] jan: P.s. A funny observation I’ve learned with tabling is that you should typically reverse the order of subgoals, e.g., specializesAll(Type, BaseType) :- specializesAll(Type, IntermediateType), rel(IntermediateType, specializes, BaseType). Doesn’t this defeat tail-call opti…

[image] ericzinda: backtracking order isn’t preserved I wouldn’t expect ordering of either goal calls or backtracking to be preserved, and I’m wondering why a program should depend on the backtracking ordering. In a “pure” Prolog program, order shouldn’t matter (as long as the program still t…

Yes, this isn’t a “pure” Prolog program. The part I’m describing above regards inheritance hierarchies, and the order matters because I want the inheritance hierarchy to go from most specific to least specific. It is used for natural language, so you almost always want to match the most specific o…

[image] ericzinda: it seems like Prolog does a good job in general of preserving order in a bunch of places. Prolog is just an inference engine, as described here: SLD resolution - Wikipedia There are many places where the ordering becomes less obvious. If I understood Jan’s answer above, fo…

[image] peter.ludemann: Doesn’t this defeat tail-call optimization? That is in the tabled case irrelevant :slight_smile: What happens is that the recursive call calls a variant of itself. Immediately for a (?,-) moded call and on the second iteration for any call. This causes the call to …

BTW, see this paper for an implementation of tabling that guarantees ordering: [image] Tabling: Linear Resolution (SLT) General This may be of interest given the new tabling work: SLT-Resolution for the Well-Founded Semantics

Are there :- table ordering guarantees?

Help!

swi January 10, 2021, 10:49pm 11

BTW, see this paper for an implementation of tabling that guarantees ordering:

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Are there :- table ordering guarantees?

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