Re: [Caml-list] ocaml 4.00.1 and 4.01.0 behave differently on module type constraint

[Ashish Agarwal <agarwal1975@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2728 bytes --]

IIUC compiling this in older versions requires making the constraint `with
type t = private Foo.t`. However, garrigue says this is not semantically
correct and has deprecated this. Okay. Thanks.



On Tue, Jan 28, 2014 at 4:43 PM, Gabriel Scherer
<gabriel.scherer@gmail.com>wrote:

> The change of behavior was part of PR#6090:
>   http://caml.inria.fr/mantis/view.php?id=6090
> It was a case of the type-checker refusing more programs than necessary.
>
> My understanding of the compatibility story of the type-system is that
> future versions will not rule out semantically valid programs accepted
> by previous ones (note that buggy programs previously accepted could
> be ruled out), but may accept strictly more semantically valid
> programs. If you need to be sure that your code compile under older
> versions, you should test them explicitely.
>
> On Tue, Jan 28, 2014 at 10:19 PM, Ashish Agarwal <agarwal1975@gmail.com>
> wrote:
> > Is the following an expected change from OCaml 4.00.1 to 4.01.0?
> >
> > Module Foo defines a private type and this module is included in Common.
> The
> > signature within Common is defined using `module type of` with a
> constraint.
> > The different behavior shown below occurs when the private type is a
> record,
> > but not if it is a base type like string or int. In that case, the code
> > compiles with both 4.00.1 and 4.01.0.
> >
> > $ cat a.ml
> > module Foo : sig
> >   type t = private {a:int}
> > end = struct
> >   type t = {a:int}
> > end
> >
> > module Common : sig
> >   module F : module type of Foo with type t = Foo.t
> > end = struct
> >   module F = Foo
> > end
> >
> > $ ocaml -version
> > The OCaml toplevel, version 4.01.0
> >
> > $ ocaml a.ml
> > (* no errors *)
> >
> > Now, change version of OCaml being used.
> >
> > $ ocaml -version
> > The OCaml toplevel, version 4.00.1
> >
> > $ ocaml a.ml
> > File "a.ml", line 9, characters 6-33:
> > Error: Signature mismatch:
> >        Modules do not match:
> >          sig module F : sig type t = Foo.t = private { a : int; } end end
> >        is not included in
> >          sig module F : sig type t = Foo.t = { a : int; } end end
> >        In module F:
> >        Modules do not match:
> >          sig type t = Foo.t = private { a : int; } end
> >        is not included in
> >          sig type t = Foo.t = { a : int; } end
> >        In module F:
> >        Type declarations do not match:
> >          type t = Foo.t = private { a : int; }
> >        is not included in
> >          type t = Foo.t = { a : int; }
> >        File "a.ml", line 8, characters 37-51: Expected declaration
> >        File "a.ml", line 2, characters 7-26: Actual declaration
> >        A private type would be revealed.
> >
>

[-- Attachment #2: Type: text/html, Size: 3854 bytes --]