在Haskell中将列表追加到列表列表中? [英] Appending lists into a list of lists in Haskell?

问题描述

在文档中我所能找到的全部是++和concat.

All I've been able to find in the documentation that are relevant are ++ and concat.

我认为首先执行以下操作会给我我想要的东西:

I thought at first doing the following would give me what I wanted:

  [1, 3, 4] ++ [4, 5, 6]

但是您知道，仅给出[1,2,3,4,5,6].

but as you know that just gives [1, 2, 3, 4, 5, 6].

我需要做什么来接受[1、2、3]和[4、5、6]并退出[[1、2、3]，[4、5、6]]?

What would I need to do to take in [1, 2, 3] and [4, 5, 6] and get out [[1, 2, 3], [4, 5, 6]]?

推荐答案

如注释中所述，将两个列表合并成一个新列表的函数可以定义为:

As mentioned in comments, a function to take two lists and combine them into a new list can be defined as:

combine :: [a] -> [a] -> [[a]]
combine xs ys = [xs,ys]

不能多次应用此功能来创建任意数量的列表的列表.这样的函数将采用一个列表和一个列表列表，并将该列表添加到列表列表中，因此其类型为:

This function can't be applied multiple times to create a list of an arbitrary number of lists. Such a function would take a single list and a list of lists and it would add the single list to the list of lists, so it would have type:

push :: [a] -> [[a]] -> [[a]]

但这只是(:)，

push = (:)

正如注释中所提到的，值[x,y]也可以写为x : y : []. ¹ 由于这两种情况都可以用(:)完成，所以我猜想您实际上是想要使用的是(:)，有时包含在[]上，有时包含在非空列表中.

As also mentioned in the comments, the value [x,y] can also be written as x : y : [].¹ Since both cases can be done with (:), I would guess that what you really want to use is (:), sometimes consing onto [] and sometimes onto a non-empty list.

¹ 实际上，[x,y]只是语法糖用于x:y:[].

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