哪种(翻转.)？

Question

我试图理解为什么类型:

(flip .) is: (a -> a1 -> b -> c) -> a -> b -> a1 -> c

首先,类型:

flip: is (a -> b -> c) -> b -> a -> c (.): is (b -> c) -> (a -> b) -> a -> c

我将在我的解释中将变量重命名为更清晰,因此类型:

flip: is (ax -> bx -> cx) -> bx -> ax -> cx (.): is (by -> cy) -> (ay -> by) -> ay -> cy

然后我尝试这样替换:

ax = (by -> cy) bx = (ay -> by) cx = ay -> cy

因此得到的类型是:(ay - > by)(by - > cy) - > ay - > cy,这与正确的结果不同.

有帮助吗？

谢谢,塞巴斯蒂安.

Answer 1

(flip .)是的(.) flip,所以:

• (.) :: (bx -> cx) -> (ax -> bx) -> ax -> cx
• flip :: (ay -> by -> cy) -> by -> ay -> cy
• 在(.) flip,
  • bx 是 ay -> by -> cy
  • cx 是 by -> ay -> cy
  • 所以这就是全部(ax -> (ay -> by -> cy)) -> ax -> (by -> ay -> cy),
    这只是(ax -> ay -> by -> cy) -> ax -> by -> ay -> cy,
    与之匹配(flip .) :: (a -> a1 -> b -> c) -> a -> b -> a1 -> c.