1) (Leaf 2)) (Fork (Leaf 3) (Leaf 4)))Fork (Fork (Leaf 1) (Leaf 4)) (Fork (Leaf 9) (Leaf 16))对于codice_31类型类的所有实例，codice_37都在契约义务上要满足函子定律：fmap id ≡ id -- 同一律fmap (f . g) ≡ fmap f . fmap g -- 复合律这里的codice_38在Haskell中指示。尤其是，它允许为各种搜集定义逐个元素的运算。此外，如果和