如何用无点样式编写这个函数？

Question

如何以无点样式重写以下函数,x完全从定义中删除参数(另外两个可能保留):

between min max x = (min < x) && (x < max)

这不是一项任务,只是一个问题.我不知道该怎么办.我可以把它变成一个lambda函数

between min max = \x -> (min < x) && (x < max)

但这不是没有点的,因为x它仍然存在.请帮忙.

Answer 1

可以使用以下Reader应用程序完成:

between min max = \x. (min < x) && (x < max)
              { Convert infix comparisons to sections }
                = \x. ((min <) x) && ((< max) x)
              { Move infix (&&) to applicative style }
                = \x. (&&) ((min <) x) ((< max) x)
              { Lift to applicative style using the applicative instance of `(->) a` }
                = \x. (pure (&&) <*> (min <) <*> (< max)) x
              { Eta-reduce }
                = pure (&&) <*> (min <) <*> (< max)
              { Optionally simplify for idiomatic style }
                = (&&) <$> (min <) <*> (< max)

Answer 2

另一种解决方案(需要导入Control.Applicative):

between min max = liftA2 (&&) (min <) (max >)