core.logic

Unification of sets allows for duplicate values leading to non-set-like behavior

Details

  • Type: Defect Defect
  • Status: Closed Closed
  • Priority: Major Major
  • Resolution: Completed
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None

Description

Considering this behavior:

user> (run* [out] (== 3 out) (== #{3 out} #{3 out}))
(3)

There are other more convoluted cases involving multiple lvars but I think the above is enough for discussion. I think the above behavior is at least unexpected (desiring documentation) if not actually incorrect behavior.

A possible solution would be to apply distincto (or some equivalent) to the members of each incoming set before the body of unify-with-set (extending IUnifyWithSet to clojure.lang.IPersistentSet). Naturally this makes set unification even more expensive than it currently is but I'm currently inclined to think that this additional cost is unavoidable, at least with the current approach.

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    Updated:
    Resolved: