[Haskell-cafe] Question on kind inference

Hi, Consider this Haskell code: ----------------------------------------------- class A a where foo :: a b class B a class (A a, B a) => C a ----------------------------------------------- GHC compiles it without errors, but Hugs rejects it: "Illegal type in class constraint". What is the correct behavior, and which part of the haskell 98 report explains this? Thanks, Vladimir