panic:Unify.unifyTauTyLists

[volkersf]

The attached sample program triggers a panic because I forgot to 
pass the type argument in the recursive algebraic datatype 
construction. The commented line is correct.
GHC should not panic but instead provide a helpful error message.
(Unluckily, I won't be able to test this with -HEAD atm)

Compiling Main             ( bugs.hs, interpreted )
ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
        Unify.unifyTauTyLists: mismatched type lists!

[simonpj]

Logged In: YES 
user_id=50165

Happily this is already fixed, and will be in 6.4.1