On 3/13/06, Jared Updike
If you want a place to start, I would challenge you to expand the concatMap definition above with the definitions of concat and map, and then plug in the definition of foldr and see if you can make your own concatMap function. Maybe that will help you understand things better.
MUHAHAHAHA I AM TEH HAXXELL GENEUS. Ahem... How's this? myhead :: [a] -> a myhead (x:xs) = x mytail :: [a] -> [a] mytail (x:xs) = xs mymap :: (a -> b) -> [a] -> [b] mymap fn [] = [] mymap fn (x:xs) = fn x : mymap fn xs myconcat :: [[a]] -> [a] myconcat (x:xs) = x ++ myconcat xs myconcat [] = [] -- For each a in [a], produce a [b] in another list, then concat the -- list. my_concat_map :: (a -> [b]) -> [a] -> [b] my_concat_map fn [] = [] my_concat_map fn xs = myconcat (mymap fn xs) stateslist :: StateNode a -> [a] stateslist(State x) = [x] stateslist (CompositeState xs) = my_concat_map stateslist xs