I agree; the problem is that I fear that making my own instance by using setToList will be very inefficient (or at least much more so than an instance which actually looks at the tree structure). -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume On Wed, 29 May 2002, Johannes Waldmann wrote:
for instance, Sets of Sets of things would be really nice.
Sure. One could simply use lexicographic ordering (i. e. s1 `compare` s2 = setToList s1 `compare` setToList s2) or length-lexicographic ordering (for efficiency) ... = (cardinality s1, setToList s1) `compare` (cardinality s2, setToList s2)
As you write, there seems to be no reason not to do this. An Ord instance should be a linear ordering, and the above are. -- -- Johannes Waldmann ---- http://www.informatik.uni-leipzig.de/~joe/ -- -- joe@informatik.uni-leipzig.de -- phone/fax (+49) 341 9732 204/252 --