用Haskell写Zipwith [英] Write Zipwith in Haskell

问题描述

我正在尝试在Haskell中编写 Zipwith 函数.

I'm trying to write the Zipwith function in Haskell.

如果我使用以下值运行它，则应返回此结果:

If I run it with the following values, it should return this result:

Prelude> zipWith (+) [10,20,30] [33,44,94]
[43,64,124]

到目前为止，我的代码是:

My code so far is:

Zipwith f [] [] = []
Zipwith f [] _ = []
Zipwith f _ [] = []
Zipwith f (x:xs) (y:ys) = (f x y) : (Zipwith f xs ys)

但是，编译器告诉我，我有多个函数，所有 Zipwith ，都没有数据定义，但是我认为在Haskell中并不需要一个.而且，然后它说我有f的多个声明，但这只是一个参数，我认为参数的多个定义无关紧要.

However, the compiler tells me that I have multiple functions, all Zipwith, that don't have a data definition, but I thought having one wasn't necessary in Haskell. Also, then it says that I have multiple declarations of f, but it is just an argument, I thought it wouldn't matter that there are multiple definitions of an argument.

有什么想法吗?

推荐答案

Haskell函数 必须 以小写字母开头.大写名称保留给其他内容，例如数据类型.在这种情况下，最好将函数命名为 zipWith'，因为'通常用于表示该函数几乎相同，但是变化很小

Haskell functions must start with a lower case. Upper case names are reserved for other stuff, like data types. In this case it would be a good idea to name your function zipWith', because ' is often used to indicate that the function is almost the same, but with a small change.

P.S.

对代码的小批判:您可以删除行 zipwith f [] [] = [] ，因为其他行已经捕获了这种情况.如果您愿意，甚至可以这样写:

Small critique of your code: You can remove the line zipwith f [] [] = [] because the other lines catch this case already. If you want you can even write it like this:

zipwith f (x:xs) (y:ys) = f x y : zipwith f xs ys
zipwith _ _ _ = []

因为第一个是您关心的唯一模式.

Since the first one is the only pattern you care about.

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