저도 한 번 훑어봤는데,
이 책에 Applicative Functor 안 나오죠?
class Functor f => Applicative F where
__ pure :: a → f a
__ <*> :: f (a → b) → f a → f b
-- APPLICATIVE'S LAWS
pure id <*> v == v -- IDENTITY
pure f <*> pure x == pure (f x) -- HOMOMORPHISM
u <*> pure y == pure ( $ y) <*> u -- INTERCHANGE
pure (.) <*> u <*> v <*> w == u <*> (v <*> w) -- COMPOSITION