永久功能应如何使用? [英] How should the forever function be used?

问题描述

我有一个功能.假设它看起来像这样:

I have a function. Let's say it looks like this:

strangeFunc = do
  putStrLn "Welcome to the game! Please, enter the name of the file: "
 --some more code

然后，我希望它永远运行，所以我这样做

Then, I want it to run forever, so I do this

strangeFunc = forever $ do
  putStrLn "Welcome to the game! Please, enter the name of the file: "
  --some more code 

但是我有一个错误:variable not in scope: forever.我该如何解决?

But I have an error: variable not in scope: forever. How can I fix it?

推荐答案

您必须从Control.Monad导入forever.将此添加到文件顶部:

You must import forever from Control.Monad. Add this to the top of your file:

import Control.Monad (forever)

当编译器说variable not in scope...时，表示我不知道这应该是什么；您尚未定义它".这可能是由于未导入所需的模块引起的.

When the compiler says variable not in scope..., it means "I don't know what this is supposed to be; you haven't defined it." This can be caused by not having the required modules imported.

我怎么知道的?如果您在Hoogle中搜索forever ，则表示它位于Control.Monad模块，位于base包中.因此，您必须导入它才能使用它.

How did I know this? If you search for forever on Hoogle, it says that it is in the Control.Monad module, in the base package. Hence, you must import it in order to use it.

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