[Haskell] Trying to get a Composite design pattern to work

I'm trying to implement hierarchical states in Haskell, following on from my work at doing them in C++. Here's what I've got so far: data StateNode a = CompositeState [ StateNode a ] | State a stateslist :: StateNode a -> [a] stateslist(State x) = [x] stateslist(CompositeState xs) = {- return list of objects of type a -} The following give errors (as they should) -- stateslist(CompositeState xs) = [ stateslist(x) | x <- xs ] -- stateslist(CompositeState xs) = map stateslist xs You see what I'm trying to do? This is how I want it to behave: sm1 = CompositeState [ State 1, State 2, State 3 ] stateslist(sm1) => [1, 2, 3] How can I get this to work? My mind has just gone all wobbly! Thanks