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To: malc@pulsesoft.com
Cc: caml-list@inria.fr
Subject: Re: Polymorphic variants in class methods
In-Reply-To: Your message of "Mon, 9 Oct 2000 02:18:06 +0400 (MSD)"
	<Pine.LNX.4.21.0010090217030.885-100000@home.oyster.ru>
References: <Pine.LNX.4.21.0010090217030.885-100000@home.oyster.ru>
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Date: Wed, 11 Oct 2000 11:35:53 +0900
From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
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From: malc <malc@pulsesoft.com>

> # class foo = object method moo = `Bar end;;
> Some type variables are unbound in this type:
>   class foo : object method moo : [> `Bar] end
> The method moo has type [> `Bar] where 'a is unbound

You can see it as a bug in the error message printer: the real message
should be

        The method moo has type ([> `Bar] as 'a) where 'a is unbound

That is, the type [> `Bar] is not fully specified (it contains a row
variable), and as a result you cannot use it in a method type, which
must be fully specified.
Easy solution, add a type annotation:
        # class foo = object method moo : [`Bar] = `Bar end;;
        class foo : object method moo : [ `Bar] end

Jacques
---------------------------------------------------------------------------
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac.jp
		<A HREF=http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>