Hello List,
With ghc - 7.8 and 7.6 the following program is accepted:
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
class (UnF (F a) ~ a, Show a) => C a where
type F a
f :: F a -> a
type family UnF a
g :: forall a. C a => a -> String
g _ = show a
where a = f (undefined :: F a) -- :: a
ghc-7.10.0.20141222 does not accept the program unless I uncomment the
type signature (a :: a).
I believe this is the main difference that prevents HList from
compiling with 7.10, but I could have made a mistake in coming up with
this minimal example.
Regards,
Adam
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