panic: "Non-exhaustive patterns in function zip_ty_env"

ghc-6.4: panic! (the `impossible' happened, GHC version
6.4):
        types/Type.lhs:(1107,0)-(1108,77):
Non-exhaustive patterns in function zip_ty_env

The same file compiles fine with GHC 6.2.2.

Unfortunately I don't have a small example of this
behaviour. I can send you the whole library if you need
it, but it is not painless to get to this point.

It would be great if you could give me some pointers
about where the bug might lie - it uses MPTC instances,
recursive newtypes and the FFI.

thanks,
peter, peteg at unsw.edu.au

Trac metadata

Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	Compiler (Type checker)
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