Re: [Caml-list] Re: Define class and sum type in one time

[Gerd Stolpmann <info@gerd-stolpmann.de>]

Am Donnerstag, den 17.03.2011, 11:50 +0100 schrieb Pierre-Alexandre
Voye:
> So, this is impossible  ?   :
> 
> class maclasse = object(self)
>   val mutable valeur = (None : truc option)
>   method getValeur = valeur
> end
> and 
> truc = Machin of (maclasse->int) | Recur of truc;; 
> 
> ?
> (three attempt to write a correct example of my problem.. All
> apologies !)

This is the closest without introducing a type variable:

type maclasse_t = < getValeur : truc option >
and truc = Machin of maclasse_t->int | Recur of truc

Here, maclasse is just an object type (which is less than a full class
type, as it has only methods but no type information about instance
variables).

In a second step you can define the class:

class maclasse = ( object ... end : maclasse_t )

Generally, it is a good recommendation to define object or class types
before doing the class implementation. Not only allows it more
complicated types but it is also easier to get the typing right, because
you have always maclasse_t at hand to give type hints.

Gerd

> 
> 2011/3/17 Guillaume Yziquel <guillaume.yziquel@citycable.ch>
>         Le Thursday 17 Mar 2011 à 11:33:44 (+0100), Pierre-Alexandre
>         Voye a écrit :
>         >    My example would be better with this :
>         >    class machin = object(self)
>         
>         >    Â  val mutable valeur = (None : truc option)
>         >    Â  method getValeur = valeur
>         >    end
>         >    and
>         >    truc = Machin of (int->int) | Recur of truc;;
>         >    The object need the type defined
>         
>         
>         You cannot declare a class and a type with an 'and'. Either
>         two classes,
>         or two types.
>         
>         Simply declare truc before machin.
>         
>         type truc = Machin of int -> int | Recur of truc
>         
>         class machin = object
>         
>                val mutable valeur : truc option = None
>         
>                method getValeur = valeur
>         
>         end
>         
>         --
>             Guillaume Yziquel
> 
> 
> 
> -- 
> ---------------------
> Isaac Project - http://www.lisaac.org/


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