According to this construction, enumeration will need some SAT enumeration like process, where you search with a new predicate barring all previous candidates? On Mon, 10 Dec, 2018, 08:50 Doug McIlroy, wrote:

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The following expressions both cause GHCI to hang:

S.intersection (S.fromList [1,2]) (S.fromList [1..]) S.intersection (S.fromList [1..]) (S.fromList [1,2])

Is there a smarter way to take the intersection of sets when at least one of them is small (but I don't know which one that is)?

"Small" is not enough. If all you know is that the lists represent sets of integers, then

S.intersection (S.fromList [-1,-2]) (S.fromList [1..])

must diverge. A sufficient condition for success in such examples is that the sets come from a well-ordered domain and are presented in order. Then it's easy to write a merge-like algorithm. Both sets can be infinite; every finite prefix of the intersection will eventually appear.

(Note that the integers are not well-ordered, though the positive integers are.)

Doug _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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