[Haskell-cafe] Class deriving in GHC 6.8

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 'deriving' clause of a data type declaration at Ert.hs:3:0-37 Possible fix: add an instance declaration for (Show (c Foo)) When deriving the instance for (Show (Bar c))

Thanks, / Emil