Re: [Caml-list] Expressing module sig and impl in mli file

[Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>]

On Wed, Sep 19, 2012 at 7:40 AM, Malcolm Matalka <mmatalka@gmail.com> wrote:
> I spoke too soon!  Below is my testcase and error.  Where did I go wrong?
>
> foo.mli:
> open Core.Std
>
> module Bar : sig
>   include Identifier with type t = String.t
> end
>
> foo.ml:
> open Core.Std
>
> module Bar : Identifier = String
>
> The error:
>        Type declarations do not match:
>          type t = Bar.t
>        is not included in
>          type t = Core.Std.String.t

First comment: there is no need to use include here.
You can just write

  module Bar : Identifier with type t = String.t

in the interface.
Since there is an interface, there is not need to restrict Bar
in the implementation, so just write:

  module Bar = String

If you want to add a signature in the implementation,
it should be a subtype of the interface signature.

Jacques Garrigue