No. I'll switch that on and report back.
Thanks,
Gabor
Em sexta-feira, 31 de julho de 2015, Simon Peyton Jones <
[email protected]> escreveu:
> you need "liberal coverage checking", so UndecidableInstances. Are you
> doing that?
>
> | -----Original Message-----
> | From: ghc-devs [mailto:[email protected] <javascript:;>] On
> Behalf Of
> | Richard Eisenberg
> | Sent: 31 July 2015 16:10
> | To: Gabor Greif
> | Cc: ghc-devs
> | Subject: Re: Fundep question
> |
> | Let's rewrite with explicit kind variables, noting that b is also
> | poly-kinded:
> |
> | class Dep k k2 (a :: k) (b :: k2) | a -> b k2
> | -- if a determines b, it surely determines k2
> |
> | instance Dep k * x y => Dep (Maybe k) * (Just x) (Maybe y)
> |
> | Actually, even with the kinds explicit, it still looks valid to me.
> | Post a bug report?
> |
> | Richard
> |
> | On Jul 31, 2015, at 9:54 AM, Gabor Greif <[email protected]
> <javascript:;>> wrote:
> |
> | > Hi all,
> | >
> | > say I want to instantiate
> | >
> | > class Dep (a :: k) b | a -> b
> | >
> | > as
> | >
> | > instance Dep x y => Dep (Just x) (Maybe y)
> | >
> | > Is this supposed to work? I get "The coverage condition fails"
> | errors.
> | >
> | > For simple cases like
> | >
> | > instance Dep True Bool
> | >
> | > etc. it seems to work fine.
> | >
> | > Thanks and cheers,
> | >
> | > Gabor
> | > _______________________________________________
> | > ghc-devs mailing list
> | > [email protected] <javascript:;>
> | > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
> |
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