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Date: Thu, 23 Jun 2011 17:43:04 +0100
Message-ID: <BANLkTi=JYJ40MRc1jONG3HT2Hg_txQe3eg@mail.gmail.com>
From: Radu Grigore <radugrigore@gmail.com>
To: caml-list <caml-list@inria.fr>
Content-Type: text/plain; charset=UTF-8
Subject: [Caml-list] module name alias and typing

The following code compiles as expected.
  module Int = struct type t = int let compare = compare end
  module Util = struct module IntSet = Set.Make (Int) end
  let a = Util.IntSet.singleton 0
  module U = Util
  let b = U.IntSet.mem 0 a

However, if the definition of Int is moved inside Util then the
type-checker complaints that Util.IntSet.t and U.IntSet.t are
incompatible.
  module Util =
    module Int = struct type t = int let compare = compare end
    struct module IntSet = Set.Make (Int)
  end
  let a = Util.IntSet.singleton 0
  module U = Util
  let b = U.IntSet.mem 0 a

I thought that "module X = Y" makes the names X and Y refer to the
same module. Is this correct?
Could someone explain what is going on in this example?

I tried with 3.11.2 and with 3.13.0+dev4 (2011-06-20).