One work-around is to define something like: instance Ord e => Ord (Set e) where compare a b = compare (setToList a) (setToList b) should work fine and shouldn't be too inefficient (I asked a similar question a while back about FiniteMap, upon which Set is built). - Hal -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Fri, 15 Nov 2002, Mark T.B. Carroll wrote:
Am I right in thinking that sets of sets don't really work with GHC's Data.Set because "Set a" things aren't instances of Ord? How should I do sets of sets with it?
(e.g. Set.mkSet [Set.unitSet 1] gives "No instance for (Ord (Set a))")
-- Mark
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