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StackOverflowError when logic variable is unified with a set

Description

It is pretty common to unify a variable with a vector or list of a fixed length like (== q (list a b)) and then define more goals on a and b with the intention of being able to define the run* query's result format. However, if one does the same using a set one gets a StackOverflowError.

Example:

Basically, what I wanted to express here is that the order of a and b is not significant so that (distinct (run* ...)) gives me the unique results.

The backtrace is:

Environment

core.logic 0.8.10, Clojure 1.7.0

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David Nolen March 27, 2024 at 5:32 PM

unification of sets is a research level problem. It unfortunately cannot be fixed with a simple patch. If you look at the original issue I state what I think would be reasonable, no logic vars in sets - they must be grounded.

Alejandro Atienza Ramos March 18, 2024 at 1:59 PM
Edited

Hey ,

The root cause of this was that PersistentSet did not implement a walk-term method, so the whole set was returned instead of its elements, and thus the infinite loop. I’ve made a very small patch reusing code from PersistentVector (so it should be quite trivial to review, by contrasting against previous lines), and provided a small test exemplifying the issue, both for Clojure and ClojureScript.

 

Thanks for all your work! Best,

Alex

PD. This is a dupe of LOGIC-130

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Created August 3, 2015 at 9:58 AM
Updated March 27, 2024 at 5:32 PM