ghc panics on accessing a labeled field

[guest]

GHC panics about a following code:

class Bar a where
	bar :: Foo a -> Foo a
	bar x = x { foo = [] }
	
data Foo a = Bar a => Foo { foo :: [a] }

GHC says:

Chasing modules from: Main.hs Compiling Main ( Main.hs, Main.o ) ghc: panic! (the `impossible' happened, GHC version 6.4.2):

types/Type.lhs:(1107,0)-(1108,77): Non-exhaustive patterns in function zip_ty_env

[simonpj]

I think this is ok in the HEAD:

Foo10.hs:7:17:
    Record update for the non-Haskell-98 data type `Foo' is not (yet) supported
    Use pattern-matching instead
    In the expression: x {foo = []}
    In the definition of `bar': bar x = x {foo = []}
    In the definition for method `bar'