RE: Fundep question

you need "liberal coverage checking", so UndecidableInstances. Are you doing that? | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] 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 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@haskell.org | > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs | | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs