[Haskell-cafe] Undecideable instances for one instance?

Bulat Ziganshin bulat.ziganshin at gmail.com
Wed Jun 7 04:28:48 EDT 2006

Hello Christophe,

Wednesday, June 7, 2006, 12:27:22 PM, you wrote:

> global instance of a typeclass (so there is no overlapping), GHC will
> still complain about overlapping. Is there any reason this is so or is

GHC compains here about undecidability, not overlapping :)

> -- Illegal instance declaration for `Locatable a'
> -- (There must be at least one non-type-variable in the instance head
> -- Use -fallow-undecidable-instances to permit this)
> -- In the instance declaration for `Locatable a'

> Christophe(vincenz)

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

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