]> What I want to do is write a class interface like: class virtual ['a] foo : object method virtual doit : 'a method map : 'b. ('a -> 'b) -> 'b foo end The map function returns a new foo (not necessarily a new member of whatever derived from foo class the function is actually being called on) parameterized on the variant type. This would be implemented more or less like: class ['a] mapped_foo f_init e_init = object val f = f_init val e = e_init method doit = f (e#doit) method map g = let h x = g (f x) in mapped_foo g e end The first prototype, when I try to compile it, returns with: File "foo.mli", line 2, characters 6-100: The abbreviation foo is used with parameters 'a foo wich are incompatible with constraints 'b foo [sic on the wich- minor typo there]. It works just fine if I change map to return a 'b list, or 'b array, or 'b Stack.t- it seems to be just 'b foo that's a problem. Am I missing something? If not, what is the suggested way for doing this? I need map as a member function- it needs to behave differently on different types, and as I don't have reflextion, I need it to be a member function. I'd prefer to keep it as a class for taste reasons. Help is appreciated. Brian ------------------- 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