Recursive Variants of Set

Hi,

Please consider my common.mli:

type id = | Id of Common.Id_set.t
          | Common of string
  | ObjStore of string

module Id_set : (Set.S with type elt = id)

Now my common.ml:

type id = | Id of Common.Id_set.t
          | Common of string
  | ObjStore of string

module Id_set = Set.Make(
    struct
      type t = id
      let compare = Pervasives.compare
    end)

The above gives an circular build error. If I change Common.Id_set.t to
Id_set.t, then I get an unbound module error - I'm assuming this is because
the Id_set module declaration is after the variant declaration.

What I'd like to know is, how would I change my Id variant to be of type
"id set"? Is this possible? The problem here is that Id_set depends on
variant id, and vice versa. How to solve this?

Thanks,

==============================
Jacques du Preez

Web: OpenLandscape.net
Twitter: @jacquesdp