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Date: Mon, 25 Mar 1996 18:22:09 +0100
To: caml-list@margaux.inria.fr
Subject: One more question about the module system
Sender: weis


Here is my problem:

I have a program implemented in several files (say m.ml, m1.ml and m2.ml).
This program depends on a module L and the dependency is expressed
using the .mli/open mechanism. So I have:

	(* m.ml *)
	open L
	open M1
	...

	(* m1.ml *)
	open L
	open M2
	...

	(* m2.ml *)
	open L
	...

I want to transform this program in order to have a functor of argument L
(i.e. I want to use twice my program with two different module L's). So
I want to be able to write (in a main.ml):

	module ML1 = M(L1)
	module ML2 = M(L2)
	...

 where M is the functor.

I use the following idea: because my different (implicit) modules
depend on L, I have to translate them into (explicit) functors. Then, I
apply the functors for m1.ml and m2.ml in the main module defined in m.ml.
The m1.ml module can no longer include an "open M2" since M2 is a functor:
m1.ml have to speak about M2 through the instantiation of M2 done in M.
So I start to write:

	(* m.mli *)
	module type L = ...
	module M(X : L) :
	  sig
	    module M1 : sig ... X.t ... end
	    module M2 : sig ... X.t ... end
	    val main : ...
	  end

	(* m.ml *)
	module M(X : L) =
	  struct
	    module M1 = M1.Make(X)
	    module M2 = M2.Make(X)
	    (* previous m.ml *)
	    let main = ...
          end

	(* m1.mli *)
	module type L = ...
	module Make(X : L) :
	  sig
	    type t1 = ...
	    val v1 : M.M(X).M2.t2
	    ...
	  end

	(* m2.mli *)
	module type L = ...
	module Make(X : L) :
	  sig
	    type t2 = ...
	    val v2 : ...
          end

For these files, it is OK but I cannot write m1.ml :

	(* m1.ml *)
	module type L = ...
	module Make(X : L) =
	  struct
	    (* previous m1.ml *)
	    let v1 = ... M.M(X).M2.v2 ...
                         ^^^^^^^^^^^^
	  end

The underlined expression is not valid. So my idea does not work.

Any hint to "functorize" my package ?


--------------
Pascal Brisset
ENAC, 7 avenue Edouard Belin, BP 4005, F-31055 Toulouse Cedex, France
Tel: +33 62 17 40 53, E-mail: pbrisset@eis.enac.dgac.fr, Fax: +33 62 17 41 43