你如何在haskell的参数中使用函数? [英] How do you use a function inside arguments in haskell?

问题描述

我遇到了一个问题，要求编写一个将函数应用于整数并计算答案的函数.问题来了:

I am on a problem that asked to write a function that applies a function to an Integer and calculate the answer. Here is the problem:

声明类型并定义一个函数，该函数接受一个函数(比如 f)和一个整数(比如 n)并返回 f 0 + f 1 + f 2 + … + f n.例如，fun sq 5 将返回 55，即 0+1+4+9+16+25(sq"的意思是正方形").

Declare the type and define a function that takes a function (say f) and an integer (say n) and returns f 0 + f 1 + f 2 + … + f n. For example, fun sq 5 would returns 55 which is 0+1+4+9+16+25 ("sq" means "square").

有人知道怎么做吗?我将不胜感激.

Does anyone know how to do that? I would very much appreciate it.

推荐答案

这叫做高阶函数

fun :: (Int -> Int) -> Int -> Int
fun f n = ???

我们只是像普通函数一样使用 f ，写 f 0 或其他什么.???是

And we just use f like a normal function, writing f 0 or whatever. ??? is the haskell translation of

 f 0 + f 1 + ... + f n

至于如何做到这一点，这看起来像家庭作业，所以我只是提示你使用 [0..n] 来获取从 0 到 n<的列表/code> 和

As for how to do this, this looks like homework so I'll just hint you to look at using [0..n] to get a list from 0 to n and

map :: (Int -> Int) -> [Int] -> [Int] -- restricting for clarity

将函数应用于列表中的每个项目(嘿，这是另一个高阶函数)

which applies a function to every item in a list (hey it's another higher order function)

sum :: [Int] -> Int

将列表中的所有数字相加.

Which adds up all the numbers in a list.

这篇关于你如何在haskell的参数中使用函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！