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 < sebf@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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