ext_cmp.mli

type 'a compare = 'a -> 'a -> int 
type ('a, 'id) cmp

(** only used for data structures, not exported for client usage *)
external getCmp : ('a,'id) cmp -> 'a compare = "%identity"

module type S = sig
  type id
  type t
  val cmp : (t,id) cmp
end

type ('key, 'id) t = 
  (module S with type t = 'key and type id = 'id)

module Make ( M : sig
    type t
    val cmp : t compare
  end) :
  S with type t = M.t

val make:
  ('a -> 'a -> int ) ->
  (module S with type t = 'a)