ghc-5.02.x: getTcTyVar

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,

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