Re: Bugs with GADTs in GHC6.4.1

> The attached script induces panic in GHC6.4.1: "ghc-6.4.1: panic! (the 
> `impossible' happened, GHC version 6.4.1): applyTypeToArgs f{v a1Eg} 
> x{v a1Ei}".

I think this is related to a known bug, because the same workaround
helps -- annotate the "f" and "x" arguments in the last line of your
program with dummy type variables, and the program will be accepted:

> zap :: Vector n (a -> b) -> Vector n a -> Vector n b
> zap fs xs = unfoldv f (len fs) (VP (fs, xs)) where
>   f :: VectorPair (a->b) a (S n) -> (b, VectorPair (a->b) a n)
>   f (VP (VCons (f :: foo) fs, VCons (x :: bar) xs)) = (f x, VP (fs, xs))

Cheers,
  Andres