相关疑难解决方法(0)

适用于Monoidal Functor:

mappend :: f         -> f   -> f
$       ::  (a -> b) ->   a ->   b
<*>     :: f(a -> b) -> f a -> f b

但是我没有在应用类型类的定义中看到有关Monoid的任何参考,你能告诉我为什么吗？

定义:

class Functor f => Applicative (f :: * -> *) where
  pure :: a -> f a
  (<*>) :: f (a -> b) -> f a -> f b
  GHC.Base.liftA2 :: (a -> b -> c) -> f a -> f b -> f c
  (*>) :: f a …