[Haskell-cafe] toSql and fromSql, for Algebraic Data Type

Hi *, The title is self-explanatory. I'd like to store information from an algebraic data type in an SQL database, but the type signature of toSql (toSql :: Data.Convertible.Base.Convertible a SqlValue => a -> SqlValue) doesn't make sense to me. How is this done (how do I make an instance of a typeclass like that?) Thanks for your time, Tom