Handle在Haskell中是半封闭的错误？ [英] Handle is semi-closed error in Haskell?

问题描述

***例外情况：< stdin>：hGetLine：非法操作（句柄为半

 <$ <$ p 
 $ b 
运行此代码后：
 c $ c> main = do 
交互$ unlines。 fmap进程。采取x。 
 readLn :: IO Int 
  

我确定原因是 take x 。有没有更好的方式来阅读只有 X使用交互行或是交互只是一个独奏球员？

解决方案

。在幕后 interact 为 hGetContents 。这使手柄变成了半封闭状态，因为它的整个输入已经被消耗（懒惰地），所以阻止你尝试进一步与句柄进行交互。尝试读取有限数字&$;

  import Control.Monad（replicateM）
 
 getLines :: Int  - > IO [String] 
 getLines n = replicateM n getLine 
  

I am getting this error in GHCI :

*** Exception: <stdin>: hGetLine: illegal operation (handle is semi-closed)

After running this code :

main = do
    interact $ unlines . fmap proccess . take x . lines
    readLn :: IO Int

And I am pretty sure the cause is take x. Is there any better way to read only x lines of input using interact or is interact just a solo player?

解决方案

What you're trying to do isn't possible with interact. Behind the scenes interact claims the entirety of stdin for itself with hGetContents. This puts the handle into a “semi-closed” state, preventing you from attempting any further interaction with the handle besides closing it, as the entirety of its input has already been consumed (lazily).

Try reading a finite number of lines with—

import Control.Monad (replicateM)

getLines :: Int -> IO [String]
getLines n = replicateM n getLine

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