哪种类型的（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

我将重命名变量更清晰在我的解释中，所以类型：

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

然后我尝试substituing这样的：

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

因此产生的类型是：（AY - >通过）（通过 - > CY） - >唉 - > CY，这与正确的结果不同。

任何帮助？

谢谢， Sebastián。

Answer 1

(flip .)(.) flip是，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
  • 所以它的所有(ax -> (ay -> by -> cy)) -> ax -> (by -> ay -> cy)，
    这只是(ax -> ay -> by -> cy) -> ax -> by -> ay -> cy，
    与(flip .) :: (a -> a1 -> b -> c) -> a -> b -> a1 -> c相匹配。