]> I guess what you're looking for are sorted arrays: 1) O(log n) lookup and insertion via binary search 2) O(n) union and intersection are simple 3) Equal sets are represented by structurally equivalent objects. -Fred > -----Original Message----- > From: owner-caml-list@pauillac.inria.fr > [mailto:owner-caml-list@pauillac.inria.fr] On Behalf Of > Harrison, John R > Sent: Friday, November 07, 2003 9:16 AM > To: erayo@cs.bilkent.edu.tr; caml-list@inria.fr > Cc: Harrison, John R > Subject: RE: [Caml-list] Efficient and canonical set representation? > > > | You basically want O(1) for set equality, I suppose. > > Actually, no --- perhaps I should have made clearer what I > *really* want. The efficiency of comparison wasn't my > motivation, but rather elegance and aesthetics. And I meant > "canonical" with respect to ordinary structural equality, not > necessarily pointer equality, so the problem is potentially a > bit easier than you might have thought. > > I want to be able to treat an abstract type in a truly > abstract way, and not worry about special-purpose equality > relations on certain types. Otherwise it's an ugly mess > dealing with complicated nestings like sets of pairs of lists of sets. > > Now, I think the right solution, conceptually speaking, is to > allow user-defined equality on abstract types. But as far as > I know this cannot be done in OCaml, and I've never met much > enthusiasm for the idea among the CAML or SML experts. > > So a poor second best is to define abstract types in a canonical way, > which was the starting-point of my question. > > After your remarks and Brian's, I'm starting to wonder if it > is possible at all to do what I want. Maybe I should be > looking for an impossibility proof instead... > > John. > > ------------------- > To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners