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Date: Mon, 29 Apr 2002 15:33:23 +0200
From: Markus Mottl <markus@oefai.at>
To: "Krishnaswami, Neel" <neelk@cswcasa.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Polymorphic Variants and Number Parameterized Typ es
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On Mon, 29 Apr 2002, Krishnaswami, Neel wrote:
> There's no recursion in the module system because that would break
> the termination guarantee.

We currently don't have this guarantee anyway:

---------------------------------------------------------------------------
module type I =
sig
  module type A
  module F :
    functor(X :
      sig
        module type A = A
        module F : functor(X : A) -> sig end
      end) -> sig end
end

module type J =
sig
  module type A = I
  module F : functor(X : I) -> sig end
end

(* Try to check J <= I *)
module Loop(X : J) = (X : I)
---------------------------------------------------------------------------

> If you think of modules as records, and functors as lambda abstractions,
> you can see that the module system defines a simply-typed lambda
> calculus. As you've noticed with C++, adding recursion to it would
> mean you can write nonterminating module expressions. (All this is
> wonderfully clearly explained in the paper, "A modular module system".)

I'd really like to see Claudio Russo's generalizations of the ML-module
system in OCaml. Especially first class modules would come really handy
to me in some situations. Any news on this front?

Regards,
Markus Mottl

-- 
Markus Mottl                                             markus@oefai.at
Austrian Research Institute
for Artificial Intelligence                  http://www.oefai.at/~markus
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