more GADT surprises

[Andres Loeh]

Surprisingly, the attached Haskell module loads successfully in ghci-6.4:

Ok, modules loaded: Main.
*Main> :t A
A :: A
*Main> :t B
B :: B []
*Main> :t B'
B' :: B [Int]
*Main> [B,B']
ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
        Unify.unifyTauTyLists: mismatched type lists!

Please report it as a compiler bug to
glasgow-haskell-bugs at haskell.org,
or http://sourceforge.net/projects/ghc/.


Best,
  Andres
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data X f = X (f ())

data A where
  A :: Int

data B a where
  B :: X []
  B' :: B [Int]