Haskell：检查两个列表是否相等 [英] Haskell: check if two lists are equal

问题描述

我想检查两个列表 A 和 B 是否相等，即 a1 == b1，a2 == b2 ，...

我有一个可行的解决方案：

 全部（\ x-> x）zipWith $（==）AB 
  

另一个想法是递归执行： a：as，b：bs ;检查 a1 == b1 ，然后使用剩余列表作为和 bs 。但没有一个更简单，更可读的方法来做到这一点？

您可以使用 == 。

 > [1，2，3] == [1，2，3] 
 True 
> [1，2，3] == [1，2] 
 False 
  

这是因为 == 是 Eq 类型类的一部分，并且有一个 Eq <
$ b $ pre $ code> instance Eq a => code $ c> instance实例列表如下所示：

公式[a]


这意味着列表实例化 Eq Eq ，除了函数和 IO 行动。

I want to check if two lists A and B are equal, i.e., a1 == b1, a2 == b2,...

I have a working solution:

all (\x->x) zipWith $ (==) A B

Another idea is to do it recursively: a:as, b:bs ; check if a1==b1 and call the function with the remaining lists as and bs. But isn't there an easier and more readable way to do this?

解决方案

You can just use == on them directly.

> [1, 2, 3] == [1, 2, 3]
True
> [1, 2, 3] == [1, 2]
False

This is because == is part of the Eq type class, and there is an Eq instance for lists which looks something like this:

instance Eq a => Eq [a]

This means that lists instantiate Eq as long as the element type also instantiates Eq, which is the case for all types defined in the standard Prelude except functions and IO actions.

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