小编kai*_*ker的帖子

如何使用ruby on rails获取网站上其他网站的页面数据？

这很有效

unique :: (a -> Bool) -> [a] -> Bool
unique p xs = 1 == length (filter p xs)

但现在我想要它的形式:

unique = (== 1) . length . filter

错误信息:

Couldn't match expected type `[a] -> Bool' with actual type `Bool'
Expected type: b0 -> [a] -> Bool
  Actual type: b0 -> Bool
In the first argument of `(.)', namely `(== 1)'
In the expression: (== 1) . length . filter

为什么这不起作用？