From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <nuffer@gmail.com>
X-Original-To: caml-list@sympa.inria.fr
Delivered-To: caml-list@sympa.inria.fr
Received: from mail2-relais-roc.national.inria.fr (mail2-relais-roc.national.inria.fr [192.134.164.83])
	by sympa.inria.fr (Postfix) with ESMTPS id F0C997EE25
	for <caml-list@sympa.inria.fr>; Thu, 13 Jun 2013 22:22:04 +0200 (CEST)
Received-SPF: None (mail2-smtp-roc.national.inria.fr: no sender
  authenticity information available from domain of
  nuffer@gmail.com) identity=pra; client-ip=209.85.212.46;
  receiver=mail2-smtp-roc.national.inria.fr;
  envelope-from="nuffer@gmail.com";
  x-sender="nuffer@gmail.com"; x-conformance=sidf_compatible
Received-SPF: Pass (mail2-smtp-roc.national.inria.fr: domain of
  nuffer@gmail.com designates 209.85.212.46 as permitted
  sender) identity=mailfrom; client-ip=209.85.212.46;
  receiver=mail2-smtp-roc.national.inria.fr;
  envelope-from="nuffer@gmail.com";
  x-sender="nuffer@gmail.com"; x-conformance=sidf_compatible;
  x-record-type="v=spf1"
Received-SPF: None (mail2-smtp-roc.national.inria.fr: no sender
  authenticity information available from domain of
  postmaster@mail-vb0-f46.google.com) identity=helo;
  client-ip=209.85.212.46;
  receiver=mail2-smtp-roc.national.inria.fr;
  envelope-from="nuffer@gmail.com";
  x-sender="postmaster@mail-vb0-f46.google.com";
  x-conformance=sidf_compatible
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: AkkBAAcpulHRVdQuk2dsb2JhbABbhAK/NwgWDgEBAQEHCxQUBCSCURkBGx4DEgkBBl0BEQEFAYgwAQMPmm6CfoxLgn+EYQoZJw1Yh3QBBQyPVINKA5dBj10WKYRRIA
X-IPAS-Result: AkkBAAcpulHRVdQuk2dsb2JhbABbhAK/NwgWDgEBAQEHCxQUBCSCURkBGx4DEgkBBl0BEQEFAYgwAQMPmm6CfoxLgn+EYQoZJw1Yh3QBBQyPVINKA5dBj10WKYRRIA
X-IronPort-AV: E=Sophos;i="4.87,861,1363129200"; 
   d="scan'208";a="21729927"
Received: from mail-vb0-f46.google.com ([209.85.212.46])
  by mail2-smtp-roc.national.inria.fr with ESMTP/TLS/RC4-SHA; 13 Jun 2013 22:22:04 +0200
Received: by mail-vb0-f46.google.com with SMTP id 10so7372125vbe.33
        for <caml-list@inria.fr>; Thu, 13 Jun 2013 13:22:03 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20120113;
        h=mime-version:date:message-id:subject:from:to:content-type;
        bh=sVGJOQn0U99nN2P58+/64dJy6E9udSxHo6ORIHXNJQY=;
        b=OO+9WAYUEIl0CFBJ1Q1Pl5iSJYemlHwroQ2CrxYIoyVJamBxcOpsMiWnmW20iXJvIk
         QR6QmlftCph7pLUXtcWJpO2fxLWi+ey/MH6VwqB8oD9V2AWXfyLCuvj8NxXTDBX9Fsqi
         7JFjX3yNZ101u8sWjgnr/xKJb+TGScZSxeyQO8vtwSevcygPilXMaQkmrw8GcQwtqK3G
         8fa3vtShg/h2Wf41EqT57lgX/wyd0pg+JyVYWQKKu68RINAJg8S971ZEl+M6JIzX5rNC
         VkjbNuwBG0wKp+67ixTONaU1p/CgnIKu8Y7d1pSL9G6mOR4+NNbOwi9mT5gVvSu30oEB
         GGqw==
MIME-Version: 1.0
X-Received: by 10.59.1.196 with SMTP id bi4mr987562ved.45.1371154923409; Thu,
 13 Jun 2013 13:22:03 -0700 (PDT)
Received: by 10.58.255.72 with HTTP; Thu, 13 Jun 2013 13:22:03 -0700 (PDT)
Date: Thu, 13 Jun 2013 16:22:03 -0400
Message-ID: <CAHZEYYOsJQFoWC8Je0k+xKHGxsfCAYe_v605unkop6_dAdi7HQ@mail.gmail.com>
From: Daniel Nuffer <nuffer@gmail.com>
To: caml-list@inria.fr
Content-Type: multipart/alternative; boundary=047d7bf0efd824586404df0ee29b
Subject: [Caml-list] Strange type error with recursive modules


--047d7bf0efd824586404df0ee29b
Content-Type: text/plain; charset=ISO-8859-1

Can anyone explain why this does not compile:

module rec A : sig
  type t
end = struct
  type z = { x : B.t }

  type t = z

  let foo t = B.foo t.x t (* Error: This expression has type t but an
expression was expected of type A.t *)
end

and B : sig
  type t
  val foo : B.t -> A.t -> unit
end = struct
  type t
  let foo _ _ = ()
end

Note that if there's no type aliasing in A, it will succeed:


module rec A : sig
  type t
end = struct
  type t = { x : B.t }

  let foo t = B.foo t.x t
end

and B : sig
  type t
  val foo : B.t -> A.t -> unit
end = struct
  type t
  let foo _ _ = ()
end

Thanks!

--047d7bf0efd824586404df0ee29b
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Can anyone explain why this does not compile:<div><br></di=
v><div><div>module rec A : sig</div><div>=A0 type t</div><div>end =3D struc=
t</div><div>=A0 type z =3D { x : B.t }</div><div><br></div><div>=A0 type t =
=3D z</div>
<div><br></div><div>=A0 let foo t =3D B.foo t.x t (* Error:=A0This expressi=
on has type t but an expression was expected of type A.t *)</div><div>end</=
div><div><br></div><div>and B : sig</div><div>=A0 type t</div><div>=A0 val =
foo : B.t -&gt; A.t -&gt; unit</div>
<div>end =3D struct</div><div>=A0 type t</div><div>=A0 let foo _ _ =3D ()</=
div><div>end</div></div><div><br></div><div style>Note that if there&#39;s =
no type aliasing in A, it will succeed:</div><div style><br></div><div styl=
e><div>
<br></div><div>module rec A : sig</div><div>=A0 type t</div><div>end =3D st=
ruct</div><div>=A0 type t =3D { x : B.t }</div><div><br></div><div>=A0 let =
foo t =3D B.foo t.x t</div><div>end</div><div><br></div><div>and B : sig</d=
iv><div>
=A0 type t</div><div>=A0 val foo : B.t -&gt; A.t -&gt; unit</div><div>end =
=3D struct</div><div>=A0 type t</div><div>=A0 let foo _ _ =3D ()</div><div>=
end</div><div><br></div><div style>Thanks!</div></div></div>

--047d7bf0efd824586404df0ee29b--