Hi Sebastian,
Is this perhaps another instance of #3851?
http://hackage.haskell.org/trac/ghc/ticket/3851
Cheers,
Pedro
On Thu, Apr 15, 2010 at 14:10, Sebastian Fischer <
s...@informatik.uni-kiel.de> wrote:
> Dear GHC experts,
>
> Certain behaviour when using
>
> {-# LANGUAGE GADTs, TypeFamilies #-}
>
> surprises me. The following is accepted by GHC 6.12.1:
>
> data GADT a where
> BoolGADT :: GADT Bool
>
> foo :: GADT a -> a -> Int
> foo BoolGADT True = 42
>
> But the following is not:
>
> data family DataFam a
> data instance DataFam Bool where
> BoolDataFam :: DataFam Bool
>
> fffuuuu :: DataFam a -> a -> Int
> fffuuuu BoolDataFam True = 42
>
> GHC 6.12.1 throws the following error (GHC 6.10.4 panics):
>
> Couldn't match expected type `a' against inferred type `Bool'
> `a' is a rigid type variable bound by
> the type signature for `fffuuuu' at gadtDataFam.hs:13:19
> In the pattern: BoolDataFam
> In the definition of `fffuuuu': fffuuuu BoolDataFam True = 42
>
> I expect that `fffuuuu` should be accepted just like `foo`. Do I expect too
> much?
>
> Cheers,
> Sebastian
>
> --
> Underestimating the novelty of the future is a time-honored tradition.
> (D.G.)
>
>
>
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