]> On Tue, 11 Nov 2003, Oleg Trott wrote: > On Sunday 09 November 2003 08:33 pm, Jacques Garrigue wrote: > > The functorial approach offers a much cleaner solution. > > I'm not convinced. > > With non-functorial sets: > > type t = Leaf of string | Node of t Set.t > > How would you do this with functorial sets? Perhaps like this: > > http://groups.google.com/groups?selm=fa.dlqsupe.1c6ajga%40ifi.uio.no > > module A : sig > type t = Leaf of string | Node of ASet.t > val compare: t -> t -> int > end > = struct > type t = Leaf of string | Node of ASet.t > let compare t1 t2 = > match (t1, t2) with > (Leaf s1, Leaf s2) -> Pervasives.compare s1 s2 > | (Leaf _, Node _) -> 1 > | (Node _, Leaf _) -> -1 > | (Node n1, Node n2) -> ASet.compare n1 n2 > end > and ASet : Set.S with type elt = A.t > = Set.Make(A) > > (BTW, that example doesn't yet work in 3.07-2 default toplevel. And couldn't > one write "let compare = Pervasives.compare" above? ) module rec A : (* a forgotten "rec" inserted *) sig type t = Leaf of string | Node of ASet.t val compare: t -> t -> int end = struct type t = Leaf of string | Node of ASet.t let compare t1 t2 = match (t1, t2) with (Leaf s1, Leaf s2) -> Pervasives.compare s1 s2 | (Leaf _, Node _) -> 1 | (Node _, Leaf _) -> -1 | (Node n1, Node n2) -> ASet.compare n1 n2 end and ASet : Set.S with type elt = A.t = Set.Make(A) It's a simple syntax error. And, if we use Pervasives.compare, we don't know for sure how the Leaf <-> Node comparison will work, do we? What if it's dependent on the order of occurrence of those constructors in the type definition? Functors can be heavy, but I prefer that approach too. Having a bit of recursiveness in the module language makes them much nicer. Now if we can just get generics... -- 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