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From: Manuel Fahndrich <maf@microsoft.com>
To: "'Markus Mottl'" <mottl@miss.wu-wien.ac.at>
Cc: caml-list@inria.fr
Subject: RE: additions to standard library?
Date: Fri, 10 Mar 2000 09:55:14 -0800
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Resent-Date: Fri, 10 Mar 2000 19:48:18 +0100
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The issue you are raising is a good one. SML/NJ can handle some of it,
because the semantics of "open" are different there. Once can actually say:

	module Foo = struct
        open B
      end

and obtain a copy of B within Foo.

This might even work to extend functors as in:

	functor Foo(Arg : A) =
        struct
           module B = Bar(A)
           open B
           let extensions = ...
        end


However, this interpretation of "open" has impacts on compilation
dependencies, in particular scoping analysis (See e.g.  "Dependency analysis
for Standard ML; Matthias Blume; ACM Trans. Program. Lang. Syst. 21, 4 (Jul.
1999), Pages 790 - 812").

-Manuel



-----Original Message-----
From: Markus Mottl [mailto:mottl@miss.wu-wien.ac.at]
Sent: Friday, March 10, 2000 12:04 AM
To: caml-redistribution@pauillac.inria.fr
Cc: caml-list@inria.fr
Subject: Re: additions to standard library?


> But  when  using functorial  interfaces  like  Set.Make,  you have  to
> redefine these  functions for each  application of the  functor. Thus,
> you  really need these  functions to  be defined  in the  functor i.e.
> together with the datatype (and, by the way, you can then define these
> functions a bit more efficiently---without using exceptions).

Exactly - this raises another question which has been bothering me from
time to time when using the module system:

How can you extend the functionality of a module without having to "copy"
the definitions of the underlying module "by hand"? In a case which I found
particularly ugly (in the "res"-library), I had to "copy" nearly 100 lines
as in:

  module Foo = struct
    module B = ...
    type t = B.t
    ...
    let iter = B.iter
    let iteri = B.iteri
    let map = B.map
    let mapi = B.mapi
    ...
  end

Everytime the other module gets extended, I have to add code by hand here,
too, to make it available. I do not see any simple workaround for this.
Extending standard libraries with needed functionality would be much easier
if there were a convenient way to get around the problem above.

Regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl