I tried the following:

module type MT =
sig
  type t
  val f: t->int
end with type t = 'x constraint 'x = [> `A];;

module N (M : MT) =
struct
  type t = [M.t | `B]
  let f: t->int = function
      `B -> 1
    | x -> M.f x
end;;

ocaml gives me:
module type MT = sig type t = [> `A] val f : t -> int end

but this latter definition is NOT accepted by OCaml:
"Unbound type parameter [..]"

The functor definition is refused because
"The type M.t is not a polymorphic variant type"

Is there a workaround?


David Monniaux            http://www.di.ens.fr/~monniaux
Laboratoire d'informatique de l'École Normale Supérieure,
Paris, France

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