为什么在Haskell中没有== (纯Nothing)返回False？

instance Eq a => Eq (Maybe a) where
    Nothing == Nothing = True
    Just x  == Just y  = x == y
    _        == _        = False

-- 定义一个简单的 Eq 实例
data Person = Person { name :: String, age :: Int } deriving (Show, Eq)

-- 创建两个相同的 Person 对象
person1 = Person "Alice" 30
person2 = Person "Alice" 30

-- 创建两个不同的 Person 对象
person3 = Person "Bob" 25

-- 使用 Maybe 包裹 Person 对象
maybePerson1 = Just person1
maybePerson2 = Just person2
maybePerson3 = Just person3
nothingPerson = Nothing

-- 比较 Maybe 值
main :: IO ()
main = do
    print $ maybePerson1 == maybePerson2  -- True，因为 person1 和 person2 相等
    print $ maybePerson1 == maybePerson3  -- False，因为 person1 和 person3 不相等
    print $ nothingPerson == nothingPerson  -- True，因为两个都是 Nothing
    print $ maybePerson1 == nothingPerson  -- False，因为一个是 Just x，另一个是 Nothing