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Date: Fri, 18 Feb 2011 22:34:39 +0100
From: Guillaume Yziquel <guillaume.yziquel@citycable.ch>
To: Jean-Louis Giavitto <jean-louis.giavitto@ircam.fr>
Cc: caml-list@inria.fr
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Subject: Re: [Caml-list] Contraintes dans la =?ISO-8859-1?Q?d=E9finitionr=E9cursiv?=e de classes

Le Friday 18 Feb 2011 à 20:50:33 (+0100), Jean-Louis Giavitto a écrit :
> Bonjour.
> 
> Je rencontre le problème suivant : une définition récursive de
> classe contraint les types paramètres de la classe, plus que je ne
> le souhaiterais.
> 
> Je ne comprend pas d'où viennent ces contraintes supplémentaires.
> Voici un exemple minimal :
> 
>    class virtual ['a, 'b] base =
>    object
>      method virtual m : 'a -> 'b derive
>    end
> 
>    and virtual ['a] derive =
>    object
>      inherit ['a, 'a] base
>    end

A solution might be to break the recursive definition and the class and
push it to a module level. You should probably be able to use recursive
modules to make "forward declarations".

yziquel@seldon:~$ ocaml
        Objective Caml version 3.12.0

# module rec M : sig
         
    class virtual ['a, 'b] base : object
      method virtual m : 'a -> 'b M.derive
    end
  
    class virtual ['a] derive : object
      inherit ['a, 'a] base
    end
  
  end = M;;
module rec M :
  sig
    class virtual ['a, 'b] base :
      object method virtual m : 'a -> 'b M.derive end
    class virtual ['a] derive :
      object method virtual m : 'a -> 'a M.derive end
  end
# 

-- 
     Guillaume Yziquel