]> Given a recursive type Fix 'a . T (where 'a occurs in T) we can unfold the type to T' = T['a -> Fix 'a.T], we define unfold t = t, if t doesn't start with a fixpoint operator. Any ideas how to best implement fold, the inverse isomorphism? Brute force method: examine every subterm, and compare with the main term using equi-recusive comparison .. this seems quadratic in the number of nodes .. smarter method: only compare arguments of fixpoint binders .. can we do any better? For example, replace the subterm in the main term with a fixpoint variable, and compare the subterm with the modified main term (directly, ie. using ocaml 'compare') [I don't know how to do this 'replacement' efficiently though] -- John Max Skaller, mailto:skaller@ozemail.com.au snail:10/1 Toxteth Rd, Glebe, NSW 2037, Australia. voice:61-2-9660-0850 ------------------- 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