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+
+{-# LANGUAGE Arrows, ExistentialQuantification #-}
+
+-- Crashed GHC 6.4 with a lint error
+-- because of the existential
+
+-- Esa Pulkkinen <esa.pulkkinen@kotiposti.net>
+-- Thomas Jäger <ThJaeger@gmail.com>
+
+module ShouldFail where
+
+class Foo a where foo :: a -> ()
+data Bar = forall a. Foo a => Bar a
+
+get :: Bar -> ()
+get = proc x -> case x of Bar a -> foo -< a
+
+-- This should be rejected because the left side of -< (here foo)
+-- should be treated as being outside the scope of the proc: it can't
+-- refer to the local variables x and a (this is enforced), nor the
+-- existentially quantified type variable introduced by unwrapping x.