困惑于haskell中的点运算符

Question

(head.group) "1234"

有效。

head.group "1234"

我收到错误：

<interactive>:8:6:
Couldn't match expected type `a0 -> [c0]'
            with actual type `[[Char]]'
In the return type of a call of `group'
Probable cause: `group' is applied to too many arguments
In the second argument of `(.)', namely `group "1234"'
In the expression: head . group "1234"

我认为（head.group）与head.group相同，为什么（head.group）工作，head.group没有。

Answer 1

由于

(head . group) "1234" = f "12345"
  where
    f = head . group

，而

head . group "1234" = head . (group "1234") 
                    = head . f
  where
    f = group "1234"

但group "1234"不是一个功能。请记住，功能应用程序比运营商更强大。