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Date: Fri, 21 Sep 2012 18:47:07 +0100
Message-ID: <CAAxsn=FTwVY757AbZHMCdMYX8Mh0DXTUYGMK_U5bRMZZRnC6vg@mail.gmail.com>
From: Jeremy Yallop <yallop@gmail.com>
To: Pierre-Etienne Meunier <pierreetienne.meunier@gmail.com>
Cc: caml-list@inria.fr
Content-Type: text/plain; charset=UTF-8
Subject: Re: [Caml-list] Partial module include

On 21 September 2012 17:43, Pierre-Etienne Meunier
<pierreetienne.meunier@gmail.com> wrote:
> module A=struct
>        let a=0
>        module B=struct let b=1 end
> end
>
> module B=struct
>        include A
>        module B=struct let b=2 end
> end

You can achieve this using destructive substitution and 'module type
of' in recent versions of OCaml:

    module A =
    struct
      let a = 0
      module B = struct let b = 1 end
    end

    module B =
    struct
      include (A : module type of A with module B := A.B)
      module B = struct let b = 2 end
    end

The 'with module B := B' construct removes the 'B' component from the
type of the 'A' module, allowing you to introduce a replacement:

    # module type ASIG = module type of A;;
    module type ASIG = sig val a : int module B : sig val b : int end end
    # module type ASIG = module type of A with module B := A.B;;
    module type ASIG = sig val a : int end

Jeremy.