Hello all!
How come in GHC 6.6 I could to write
{-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-}
data Foo = Foo deriving Show
data Bar c = Bar (c Foo) deriving Show
but in GHC 6.8.2 I get the error
No instance for (Show (c Foo))
arising from the
After looking more closely at user's manual, I just found that the following
works:
{-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances #-}
data Foo = Foo deriving Show
data Bar c = Bar (c Foo)
deriving instance Show (c Foo) = Show (Bar c)
/ Emil
On 2007-12-20
