[Caml-list] include two module implementations sharing the same type definitions

["Yann Régis-Gianas" <yrg@irif.fr>]

[-- Attachment #1: Type: text/plain, Size: 1180 bytes --]

Dear OCaml module hackers,

the recently polished "substitution inside type signature" (described in
Sec 8.11 in the manual) is a real improvement to modularize module
signature developments.

Yet, it seems to me that "include" at the level of module implementations
is preventing us to unleash the full composability power of "include" at
the level of signature. Consider the following example:

``
module type A = sig type t end

module type B = sig type t end

type u = U

module AI : A with type t = u = struct
  type t = u
end

module BI : B with type t = u = struct
  type t = u
end

module ABI : sig
  include A
  include B with type t := t
end = struct
  include AI
  include BI (* This include unfortunately triggers:

Error: Multiple definition of the type name t.
       Names must be unique in a given structure or signature.

  *)
end
``

I have two questions:

Would it make sense to allow module implementation inclusion to introduce
multiple definitions of a given type name as long as these definitions are
equivalent?

Is there an idiom to work around this (apparent) limitation?

Cheers,
-- 
Yann Régis-Gianas

[-- Attachment #2: Type: text/html, Size: 1799 bytes --]