Re: [Caml-list] module alias in a .mli file

[Francois Berenger <berenger@riken.jp>]

On 11/20/2012 12:46 AM, Tiphaine Turpin wrote:
> In fact, the solution
>
>    module V3 : module type of Vector3
>
> does not work completely, because, the equality between Vector3 and V3
> is lost, which poses problem with the types defined by Vector 3. What
> works is:
>
>    include module type of struct module V3 = Vector3 end

It's a little verbose but might be closer to what I was looking for.

> Here is a full example:
>
> module M : sig
>
>    module Vector3 : sig type t end
>    (* module V3 : module type of Vector3 *)
>    include module type of struct module V3 = Vector3 end
>
> end = struct
>
>    module Vector3 = struct type t end
>    module V3 = Vector3
>
> end
>
> open M
> let id (x : Vector3.t) : V3.t = x
>
>
> Regards,
>
> Tiphaine
>
>
> On 11/19/12 13:44, Paolo Donadeo wrote:
>>
>> Actually this is not true, Martin explained how. :-)
>>
>>
>> --
>> Paolo
>> Sent by Gmail from Android
>>
>> Il giorno 19/nov/2012 11:35, "David House" <dhouse@janestreet.com
>> <mailto:dhouse@janestreet.com>> ha scritto:
>>
>>     Annoyingly though, there is no way to create a module alias in an mli.
>>
>>     If, in an ml file, you have to refer often to
>>     Some_very_long_module_name, it can quite convenient to define an alias
>>     by doing "module Mod = Some_very_long_module_name" (or, locally, "let
>>     module Mod = Some_very_long_module_name in"). But there is no way of
>>     doing this in an mli: you have to use the long name every time.
>>
>>     This is especially annoying if you have some big type that you want to
>>     expose in the mli. You really just want to copy-paste out of the ml
>>     file and stick it into the mli, but then you have to expand all the
>>     module aliases. (It's just a couple of goes with M-%, but still...)
>>
>>     On Mon, Nov 19, 2012 at 6:36 AM, Francois Berenger
>>     <berenger@riken.jp <mailto:berenger@riken.jp>> wrote:
>>     > On 11/19/2012 03:02 PM, Martin Jambon wrote:
>>     >>
>>     >> On Sun 18 Nov 2012 09:29:31 PM PST, Francois Berenger wrote:
>>     >>>
>>     >>> Hello,
>>     >>>
>>     >>> Here is my stupid question of the day:
>>     >>> can't I declare the following in a .mli file?
>>     >>>
>>     >>> module V3 = Vector3
>>     >>
>>     >>
>>     >> No, because "= Vector3" specifies an implementation.
>>     >> An mli file is a module interface, and module interfaces never
>>     contain
>>     >> implementations.
>>     >>
>>     >> However, you may want to do this, which does what it says:
>>     >>
>>     >>   module V3 : module type of Vector3
>>     >
>>     >
>>     > Thanks a lot! That's exactly what I needed. :)
>>     >
>>     >
>>     >
>>     >
>>     > --
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>