在 Haskell 中添加列表的惯用方法是什么？

发布于 2024-10-13 09:12:17 字数 201 浏览 2 评论 0原文

假设我想在 Haskell 中添加两个列表。最常用的方法是什么？

这就是我所做的：

addLists :: (Integral a) => [a] -> [a] -> [a]
addLists xs ys = map add $ zip xs ys
    where add (x, y) = x+y

原文

Suppose I want to add two lists in Haskell. What is the most usual way to do this?

Here's what I did:

addLists :: (Integral a) => [a] -> [a] -> [a]
addLists xs ys = map add $ zip xs ys
    where add (x, y) = x+y

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天涯沦落人 2024-10-20 09:12:17

有一个 zipWith 使用提供的函数组合两个列表的库函数。它完全按照您的要求进行操作，您将得到：

addLists = zipWith (+)

这使用 (+) 来组合作为进一步参数给出的列表元素。

There is a zipWith library function that combines two lists by using a supplied function. It does exactly what you want here and you get:

addLists = zipWith (+)

This uses (+) to combine the elements of lists given as further arguments.

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沐歌 2024-10-20 09:12:17

Applicative Functor 风格：

import Control.Applicative

addLists xs ys = getZipList $ (+) <gt; ZipList xs <*> ZipList ys

请注意，这非常丑陋，因为有两种方法可以使 List 成为 Applicative Functor。第一种（恕我直言，不太有用）方法是采用所有组合，这种方法成为“标准”，所以 (+) <$> [1,2] <*> [30,40] 是 [31,41,32,42]。另一种方法是根据我们的需要压缩列表，但由于每种类型只能有一个类型类实例，因此我们必须将列表包装在 ZipLists 中，并使用 getZipList 解开结果。

Applicative Functor style:

import Control.Applicative

addLists xs ys = getZipList $ (+) <gt; ZipList xs <*> ZipList ys

Note that this is so ugly because there are two ways to make List an Applicative Functor. The first (and IMHO less useful) way is to take all combination, and that way became the "standard", so (+) <$> [1,2] <*> [30,40] is [31,41,32,42]. The other way is to zip the lists as we need here, but as you can have only one type class instance per type, we have to wrap the lists in ZipLists, and to unwrap the result using getZipList.

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