Eta-contraction gives a rather bogus type error message

Consider the following program:

module Main where

type T a = Show a => a

f :: T a -> String
f = show

Compiling this with GHC 6.10.3 and -fglasgow-exts gives:

[1 of 1] Compiling Main             ( Test.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.3 for i386-apple-darwin):
	TcTyFuns.flattenType: unexpected PredType

Trac metadata

Trac field	Value
Version	6.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	thomas@cs.ru.nl
Operating system	MacOS X
Architecture	x86