Introspection in Haskell is provided by the Data.Generics module.

The difference between the Data.Typeable and HList approach is that Generics use run-time information to make choises, HLists use the type system to make static guarantes. You can actually combine the two quite nicely and end up with statically constrained dynamics (or Stanamics as Ralf calls them) ... That is a dynamic opaque container constrained to contain only a certain group of types statically! Keean.