Dear Group, When trying to run the example at: http://www.cs.vu.nl/boilerplate/testsuite/gzip/Main.hs ghc 6.10.1 says A pattern type signature cannot bind scoped type variables `a' unless the pattern has a rigid type context In the pattern: f :: a -> a -> a In the definition of `mkTT': mkTT (f :: a -> a -> a) x y = case (cast x, cast y) of { (Just (x' :: a), Just (y' :: a)) -> cast (f x' y') _ -> Nothing } In the definition of `main': main = print $ gzip (mkTT maxS) genCom1 genCom2 where genCom1 = everywhere (mkT (double "Joost")) genCom genCom2 = everywhere (mkT (double "Marlow")) genCom double x (E (p@(P y _)) (S s)) | x == y = E p (S (2 * s)) double _ e = e maxS (S x) (S y) = S (max x y) .... Failed, modules loaded: CompanyDatatypes. --------------------------------------------------------------------- I must admit I don't really know what to make of this. Any insights would be appreciated. Thanks. Henry Laxen