理解 Haskell 的斐波那契数列 [英] Understanding Haskell's fibonacci

问题描述

fibs :: [Int]
fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)]

这会生成斐波那契数列.

This generates the Fibonacci sequence.

我理解 :、zip 和 tail 守卫的行为，但我不理解 <- .它在这里做什么?

I understand the behaviour of the guards, of :, zip and tail, but I don't understand <-. What is it doing here?

推荐答案

由于点赞，我将评论变成了答案.

Due to the upvotes I made my comment into an answer.

你看到的不是守卫，而是列表理解.首先，将其视为一种表达数学集合符号的方式，例如 A = { x |x 元素 N } 表示以下内容: 集合 A 是所有自然数的集合.在列表理解中，这将是 [x |x <- [1..] ].

What you see is not a guard but it is list comprehension. For starters think of it as a way to express a mathematical set notation like A = { x | x element N } which means something along the lines of: The set A is the set of all natural numbers. In list comprehension that would be [x | x <- [1..] ].

您还可以对数字使用约束:[x |x <- [1..], x `mod` 2 == 0 ] 和许多其他的东西.

You can also use constraints on your numbers: [x | x <- [1..], x `mod` 2 == 0 ] and many other things.

有很多不错的haskell turorials，涵盖了列表理解，甚至还有一个关于haskell 资源的StackOverflow 问题.

There are alot of good haskell turorials out there that cover list comprehension and even a StackOverflow question regarding haskell resources.

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