ghc-5.02.x: getTcTyVar

[Armin Groesslinger]

Hello,

when I try to compile the program below with "ghc -fglasgow-exts
-fallow-undecidable-instances"  ghc-5.02.1 and 5.02.2 (from today's
CVS) go into an infinite loop saying

getTcTyVar c{-r4D-}

all the time instead of complaining for the missing
instance X T c  to derive  Show S .


Regards,

Armin



module Test where

data T = T Integer

class X a b | a -> b where
    f :: a -> b

instance X T c => Show T where
    show _ = ""

data S = S T deriving Show