Tue, 4 Sep 2001 21:12:41 +0300, Eray Ozkural pisze:

Thanks for the suggestion, but isn't this a bit inefficient? Ordinarily one would like to compare two elements of a set by reference, not by content.

There is no such thing in Haskell. mkSet [mkSet [1, 2]] is indistinguishable from mkSet [mkSet [1, 2]] even if {1,2} sets were created independently. Whether representations of particular mkSet [1, 2] objects are shared is an implementation detail. Well, there are compiler-dependent unsafe functions which could detect sharing, but they are not normally used. Functional programming is about values, not about objects with identities. You could implement a "tagged object" type, like data Tagged a = Tagged Integer a give objects unique numbers as they are created, and make Eq and Ord instances which compare these numbers only, ignoring the real value. -- __("< Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK