On 05/19/2010 02:24 PM, Christophe Raffalli wrote:
> Does anyone see a way to avoid it

I propose:


module rec T : sig
   type t = U.t
   val compare : t -> t -> int
end = struct
   include U

   let compare u v = match u, v with
     Leaf, Leaf -> 0
   | Node u', Node v' -> S.compare u' v'
   | Leaf, Node _ -> -1
   | Node _, Leaf -> 1
end

and S : Set.S with type elt = T.t = Set.Make(T)

and U : sig
   type t =
     Node of S.t
   | Leaf
end = U


The type definition is given only once.


-- Alain