-- 9
altMap :: (a -> b) -> (a -> b) -> [a] -> [b]
altMapf :: (a -> b) -> (a -> b) -> [a] -> [b]
altMapg :: (a -> b) -> (a -> b) -> [a] -> [b]
altMap f g xs = altMapf f g xs

altMapf f g xs
  | null xs = []
  | otherwise = [f $ head xs] ++ (altMapg f g (tail xs))

altMapg f g xs
  | null xs = []
  | otherwise = [g $ head xs] ++ (altMapf f g (tail xs))