[Haskell-cafe] ambiguous partially defined type problem

Bulat Ziganshin bulat.ziganshin at gmail.com
Thu Sep 14 12:02:38 EDT 2006

Hello Brian,

Thursday, September 14, 2006, 7:43:55 PM, you wrote:

> Even if the compiler did know, by some other means, that a Node had been
> wrapped, Haskell doesn't support true existentials

> whereas you'd really need an existential:

>     getCommon :: (forall gc. Node gc) -> Common

they are supported in ghc 6.6 with name of "impredicative
polymorphism", section 7.4.9 or 7.4.10 of new user manual

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com

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