[Caml-list] Mixed class / type

[Caml-list] Mixed class / type

[Warp]

Hello,

I got this problem :
- two classes called wmenu and wmenuitem, are mutaly recursive
- one wmenuitem can be constructed either with a wmenu or with a wmenuitem

so I need a type like this :

type menu =
    Mainmenu of wmenu
    | Menuitem of wmenuitem

So I tryied :

type menu = .....
and
    class wmenuitem : menu -> object ... end
and
    class wmenu : object ... end

But it doesn't work.
Any clue is welcomed.

Warp

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Re: [Caml-list] Mixed class / type

[Remi VANICAT]

"Warp" <warplayer@free.fr> writes:

> Hello,
> 
> I got this problem :
> - two classes called wmenu and wmenuitem, are mutaly recursive
> - one wmenuitem can be constructed either with a wmenu or with a wmenuitem
> 
> so I need a type like this :
> 
> type menu =
>     Mainmenu of wmenu
>     | Menuitem of wmenuitem
> 
> So I tryied :
> 
> type menu = .....
> and
>     class wmenuitem : menu -> object ... end
> and
>     class wmenu : object ... end
> 
> But it doesn't work.
> Any clue is welcomed.

This problem already have been answer. :

type ('a, 'b) menu_t =
     Mainmenu of 'a 
   | Menuitem of 'b

class wmenuitem : (wmenuitem, wmenu) menu_t -> object .... end
and wmenu : object ... end

type menu = (wmenuitem, wmenu) menu_t

-- 
Rémi Vanicat
vanicat@labri.u-bordeaux.fr
http://dept-info.labri.u-bordeaux.fr/~vanicat
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Re: [Caml-list] Mixed class / type

[Jacques Garrigue]

> I got this problem :
> - two classes called wmenu and wmenuitem, are mutaly recursive
> - one wmenuitem can be constructed either with a wmenu or with a wmenuitem
> 
> so I need a type like this :
> 
> type menu =
>     Mainmenu of wmenu
>     | Menuitem of wmenuitem
> 
> So I tryied :
> 
> type menu = .....
> and
>     class wmenuitem : menu -> object ... end
> and
>     class wmenu : object ... end
> 
> But it doesn't work.
> Any clue is welcomed.

A light workaround would be

class wmenuitem : [ `Mainmenu of wmenu | `Menuitem of wmenuitem] -> ...
and wmenu : object ... end

Since polymorphic variants do not need to be defined, the problem does
not appear.

    Jacques Garrigue
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Re: [Caml-list] Mixed class / type

[Hendrik Tews]

Warp writes:
   From: "Warp" <warplayer@free.fr>
   Date: Wed, 30 Jan 2002 17:03:44 +0100
   Subject: [Caml-list] Mixed class / type
   
   type menu = .....
   and
       class wmenuitem : menu -> object ... end
   and
       class wmenu : object ... end
   

The real solution would be to allow variant types and classes (or
at least class types) to be mutually dependent. 

Why is this forbidden in ocaml?

Bye,

Hendrik
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Re: [Caml-list] Mixed class / type

[Jacques Garrigue]

From: Hendrik Tews <tews@tcs.inf.tu-dresden.de>

> The real solution would be to allow variant types and classes (or
> at least class types) to be mutually dependent. 
> 
> Why is this forbidden in ocaml?

The first reason is technical: class types and type declarations are
handled in two different modules, and integrating them would not be
easy.

But there are also more theoretical problems.
Basically, recursion between class types is monomorphic (to allow
propagation of type constraints), while it is polymorphic between type
declarations. So the meaning of a combined declaration is yet to be
defined.

Regards,

Jacques Garrigue
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