满足条件时如何摆脱迭代循环? [英] How to get out of iterate loop when a condition is met?

问题描述

我想用 iterate 遍历函数 g .当我运行代码时，循环将无限运行.满足条件时是否有可能脱离循环?

I want to iterate over a function g with iterate. When I run my code the loop runs infinitely. Is there any possibility to get out of the loop when a condition is met?

类似于 if g x>100，然后停止.

我的代码:

f x = iterate g x

g x = 2 * x

推荐答案

是的，您可以使用 takeWhile(不是.p)来实现，等同于

Yes, you either use takeWhile (not . p) for that, equivalent to

foldr (\x r -> if (not (p x)) then (x:r) else []) []

或者有时以下有用，

takeUntil p = foldr (\x r -> if (not (p x)) then (x:r) else [x]) []

如果您也想在序列中包含最后一个元素.

if you want to include the last element into the sequence, as well.

在您的情况下，您将编写 takeWhile(不是.(> 100)).迭代(* 2)或 takeUntil(> 100).重复(* 2).

In your case, you'd write takeWhile (not . (> 100)) . iterate (*2), or takeUntil (> 100) . iterate (*2).

(不是.(> 100))当然与(< = 100)相同.

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