Question

haskell中是否有一些函数在一个列表遍历中求值（过滤p xs，filter（not.p）xs）（这里有两个）或者在函数式编程中是否有一些这种函数的通用名称？ / p>

Answer 1

首先看一下你需要的类型：

Prelude> :t \p xs -> (filter p xs, filter (not . p) xs)
\p xs -> (filter p xs, filter (not . p) xs)
  :: (a -> Bool) -> [a] -> ([a], [a])

Hoogle is your friend：

Prelude> :hoogle (a -> Bool) -> [a] -> ([a], [a])
Prelude break :: (a -> Bool) -> [a] -> ([a], [a])
Prelude span :: (a -> Bool) -> [a] -> ([a], [a])
Data.List break :: (a -> Bool) -> [a] -> ([a], [a])
Data.List partition :: (a -> Bool) -> [a] -> ([a], [a])
Data.List span :: (a -> Bool) -> [a] -> ([a], [a])

现在试试这些功能：

Prelude> break odd [1..10]
([],[1,2,3,4,5,6,7,8,9,10])
Prelude> span odd [1..10]
([1],[2,3,4,5,6,7,8,9,10])
Prelude> import Data.List
Prelude Data.List> partition odd [1..10]
([1,3,5,7,9],[2,4,6,8,10])

Answer 2

Haskell称之为partition。

Answer 3

我想你想要Data.List.partition，例如

partition (>2) [1,2,3,4,5]

结果为([3,4,5], [1,2])

标准名称（过滤器p xs，过滤器（not.p）xs）

3 个答案: