I couldn't think of a better way to describe what I'm trying to do, so forgive the possibly strange subject!

In:

module IntSet = Set.Make(struct type t = int let compare = compare end)

the resulting signature is:

sig

  type elt = int

  type t

  ...

but in:

module FlagSet = Set.Make(struct type t = A | B let compare = compare end)

the resulting signature is:

sig

  type elt

  type t

  ...

i.e. the constructors are hidden (I can see why, but presumably it is a special case in the type checker?) and the module is essentially useless. I don't want to define the type external to the module - the idea is that I'd be able to write Flag1Set.add Flag1Set.CommonFlag Flag1Set.empty and Flag2Set.add Flag2Set.CommonFlag Flag2Set.empty, etc.

I can work around this by writing:

module FlagSet =

  struct

    type flag = A | B

    include Set.Make(struct type t = flag let compare = compare end)

  end

where the resulting signature is:

sig

  type flag = A | B

  type elt = flag

  type t

  ...

but I'm wondering:

a) Is there a way to do it where you can end up with type elt = A | B (I think the answer is no?)

b) Is there a syntactically lighter way to write the module definition?

David