]> Pierre Weis writes: As you should already know, usual sum and product types in Caml correspond to the mathematical notion of free algebraic data structures. If you consider the ocaml fragment without recursive values. For instance: type nat = | Zero | Succ of nat;; let rec x = Succ x;; This x does not belong to the free algebra. (And BTW, the product types are not free, they are cofree or terminal or final, whatever terminology you prefer.) Sorry for nitpicking, Hendrik Tews ------------------- 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