相关疑难解决方法(0)

所以,我想手动证明Maybe applicative的组成法则是:

u <*> (v <*> w) = pure (.) <*> u <*> v <*> w

我用这些步骤证明了这一点:

u <*> (v <*> w)          [Left hand side of the law]
  = (Just f) <*> (v <*> w)  [Assume u ~ Just f]
  = fmap f (v <*> w)
  = fmap f (Just g <*> w)   [Assume v ~ Just g]
  = fmap f (fmap g w)
  = fmap (f . g) w

pure (.) <*> u <*> v <*> w  [Right hand …