更简单的groupStartBy函数？

Question

我在第二次在不相关的项目中编写以下函数(首先是XML处理,现在是自定义命令行标记处理),我感觉它应该存在于某个库中,我只是找不到它.它对列表元素进行分组,每个组从谓词为真的元素开始.

有任何更简单的方法吗？

groupStartBy :: (a -> Bool) -> [a] -> [[a]]
groupStartBy pred xs = reverse $ map reverse $ foldl' step [] xs
  where
    step as x | pred x = [x]:as
    step (a:as) x = (x:a):as
    step [] x = [[x]]

Answer 1

你可以groupBy这样做:

import Data.List (groupBy)

groupStartBy :: (a -> Bool) -> [a] -> [[a]]
groupStartBy pred = groupBy (const (not . pred))
-- or in point free style: groupStartBy = groupBy . const . (not .)