Deriving instances of existentials

[Marcin 'Qrczak' Kowalczyk]

The program

data Ex = forall a. Ex [a] deriving Eq
main = print (Ex "abc" == Ex "abc")

causes ghc-4.04 to die with

Subst.lhs:199: Non-exhaustive patterns in function zip_ty_env

-- 
 __("<    Marcin Kowalczyk * [EMAIL PROTECTED] http://qrczak.ids.net.pl/
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QRCZAK                  5? X- R tv-- b+>++ DI D- G+ e>++++ h! r--%>++ y-