Hello, I had a question about type classes and data types. I want to create one class that has a function which depends upon a parameter from another class. I would assume that this can be done, but I can't seem to write code that does it. Can anybody tell me what is wrong? Here is an example of what I want to work: module Main where class Change c class State st where transitions :: (Change c) => st -> [(c, st)] data BinState = On | Off data BinChange = OnToOff | OffToOn -- get a list of (transition, newState) pairs: --binTransitions :: BinState -> [(BinChange, BinState)] -- doesn't work --binTransitions :: (State state, Change change) => state -> -- [(change, state)] -- doesn't work --binTransitions :: (State state1, State state2, Change change) => -- state1 -> [(change, state2)] -- doesn't work binTransitions On = [(OnToOff, Off)] binTransitions Off = [(OffToOn, On)] instance Change BinChange instance State BinState where transitions = binTransitions main = putStrLn "success." -- Thanks, -- -Chaim