Fundep question

[Gabor Greif]

No. I'll switch that on and report back.

Thanks,

    Gabor

Em sexta-feira, 31 de julho de 2015, Simon Peyton Jones <
simonpj at microsoft.com> escreveu:

> you need "liberal coverage checking", so UndecidableInstances. Are you
> doing that?
>
> |  -----Original Message-----
> |  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org <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 <ggreif at gmail.com
> <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
> |  > ghc-devs at haskell.org <javascript:;>
> |  > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
> |
> |  _______________________________________________
> |  ghc-devs mailing list
> |  ghc-devs at haskell.org <javascript:;>
> |  http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-devs/attachments/20150731/c28939ed/attachment.html>