Write myFilter in terms of foldr. It should have the same behavior as the
-- built-in filter.
myFilter :: (a -> Bool) -> [a] -> [a]
myFilter f = foldr (\x y -> case f x of
                                   True -> x : y
                                   False -> y) []

-- 7
myFilter :: (a -> Bool) -> [a] -> [a]
myFilter f = foldr (\x y -> case f x of
                                   True -> x : y
                                   False -> y) []
myFilter f = foldr (\x y -> case f x of
                                   True -> x : y
                                   False -> y) []