haskell-将超过 1 个参数传递给 monad

我正在学习 Haskell 并编造一些例子。我不确定为什么第二个示例不起作用

foo :: Int -> Int -> Maybe Int
foo 0 0 = Nothing
foo a b = Just $ a + b

bar :: Int -> Maybe Int
bar 0 = Nothing
bar a = Just $ a + 1

-- This works
Just 4 >>= bar

-- Why this doesnt work?
(Just 4 Just 4) >>= foo

-- This works
do
    a <- Just 3
    b <- Just 4
    foo a b

非常感谢。