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From: Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>
In-Reply-To: <001601ce6fe1$a2ea9390$e8bfbab0$@metastack.com>
Date: Mon, 24 Jun 2013 08:15:38 +0900
Cc: "OCaml List" <caml-list@inria.fr>
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References: <001601ce6fe1$a2ea9390$e8bfbab0$@metastack.com>
To: David Allsopp <dra-news@metastack.com>
X-Mailer: Apple Mail (2.1508)
Subject: Re: [Caml-list] Anonymous sum types in functors

On 2013/06/23, at 16:16, David Allsopp <dra-news@metastack.com> wrote:

> module FlagSet =3D Set.Make(struct type t =3D A | B let compare =3D compa=
re end)
[doesn't work]
> but I'm wondering:
>=20=20
> a) Is there a way to do it where you can end up with type elt =3D A | B (=
I think the answer is no?)

Xavier described the official solution.
However, since 3.12 you can also do some trickery.
This is going to be heavier, so this is probably a bad idea, but if you rea=
lly need it, here it is:

module FlagSet =3D struct
  type elt =3D A | B
  include (Set.Make (struct type t =3D elt let compare =3D compare end) : S=
et.S with type elt :=3D elt)
end

Jacques Garrigue=