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From: Peng Zang <peng.zang@gmail.com>
To: caml-list@yquem.inria.fr
Cc: Samuel Mimram <samuel.mimram@ens-lyon.org>
Subject: Re: [Caml-list] Objects and variants
Date: Fri, 6 Mar 2009 11:10:10 -0500	[thread overview]
Message-ID: <200903061110.12728.peng.zang@gmail.com> (raw)
In-Reply-To: <49B147F7.4090303@ens-lyon.org>

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You're looking for a polymorphic method:

class a = object
  method f : 'a. ([>] as 'a) -> unit = fun _ -> ()
end

Peng

On Friday 06 March 2009 10:57:43 am Samuel Mimram wrote:
> Hi,
>
> When I try to compile the following code:
>
> class a =
> object
>   method f (x:[>]) = ()
> end
>
> I get the following error:
>
> Error: Some type variables are unbound in this type:
>          class a : object method f : [>  ] -> unit end
>        The method f has type ([>  ] as 'a) -> unit where 'a is unbound
>
> Is the binding of [>] to 'a really necessary here? In particular it is
> not mentioned in the inferred type...
>
> Of course I can parametrize the class over 'a as
>
> class ['a] a =
> object
>   method f (x:[>] as 'a) = ()
> end
>
> which now has type
>
> class ['a] a : object constraint 'a = [>  ] method f : 'a -> unit end
>
> But this seems rather cumbersome. Is there a way to handle this without
> mentioning 'a?
>
> Thanks!
>
> Cheers,
>
> Samuel.
>
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      reply	other threads:[~2009-03-06 16:10 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-03-06 15:57 Samuel Mimram
2009-03-06 16:10 ` Peng Zang [this message]

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