Andre, Thanks for paper pointers.
Hmm, what's the higher goal of what you're trying to achieve? I, like you, came from a background of object-oriented programming, and I've always managed to avoid making a list containing more than one type after re-thinking about the problem. You can do it, sure, but the typical reasons for doing so in Haskell are very different from doing this in, say, Java.
I'm simulating the interaction of different physical entities with particles. Basically I have this: class PhysicalObject a where interact1 :: a -> InteractionParameters -> InteractionResult Also I have the Scene data structure, which has the list of physical objects, read from a configuration file. data Scene = Scene {....., objects :: [AnyPhysicalObject], ....} The Scene is than passed to different simulation algorithms type Simulator = Scene -> SimulationResult All the simulators don't care about different PhysicalObjects. They are even mostly pluggable. All simulator should know is the object interaction with particles. Regards, Mike