specializing on existentially quantified data types

Hi all, Suppose you have: class C a where ... data MkC = forall a . C a => MkC a foo :: MkC -> ... and I want to specialize foo for when the 'a' in the MkC is, say, Int. Is this possible? -- Hal Daume III | hdaume@isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume