[Haskell-cafe] GHC API: type class instance check

Hi all, I'm writing a core-to-core GHC plugin and have two questions: - Given some t :: Type, how can I check whether there exists an instance of some type class C for t? - How can I check whether some type class C exists, and if so, how can I get a value c (presumably :: Class) of this class? Thanks! - Jurriën