fun :: Num a => (a -> a) -> (a -> Bool) -> [a] -> [a]
fun f p xs = map f (filter p xs)

map' :: (a -> b) -> [a] -> [b]
map' f xs = foldr ((:).f) [] xs

filter' :: (a -> Bool) -> [a] -> [a]
filter' p xs = foldr (\x xs -> if (p x) then x:xs else xs) [] xs

altMap :: (a -> b) -> (a -> b) -> [a] -> [b]
altMap fa fb xs = map
    (\(x, val) -> if x then fa val else fb val)
    (zip [x `mod` 2 == 1 | x <- [0..((length xs) - 1)]] xs)