haskell-跳过getLine [英] haskell -skipping getLine

问题描述

嘿-优秀的编码人员和散客， 我是Haskell新生，程序有问题 归结为以下情况

hey - great coders and haskellers, i'm a haskell freshman and have a problem with a program it boils down to the following situaition

main :: IO ()
main = do
    putStrLn "\nplease give me some input"
    input1 <- getLine
    putStrLn "\nplease give me another input"
    input2 <-getLine
    putStrLn ("\nyour inputs were "++show(input1)++" and "++ show(input2)")
    putStrLn "restart ?? yY or nN"
    c <- getChar
    restart c
    where 
    restart c
        |elem c "yY" = do
            main
        |elem c "nN" = putStrLn "\nExample Over"
        |otherwise = do
            putStrLn "\nyou must type one of Yy to confirm or nN to abort"
            c'<- getChar
            restart c'

除main的首次执行外的任何内容

on any but the first execution of main

input1 <- getLine

被跳过，我找不到原因，如下所示

is skipped and i can find no reason for it, as the following

input2 <- getLine

按预期执行，我愿意接受任何建议和帮助 在此先感谢ε/2

is executed as expected, i'm open for any suggestions and help thanks in advance ε/2

推荐答案

解决方法:在程序开始时设置NoBuffering:

The fix: set NoBuffering at the start of your program:

hSetBuffering stdin NoBuffering

为什么这可以解决问题?查看不使用NoBuffering时要输入的内容！您键入，并且getLine使用:

Why does this fix the issue? Look at what you're typing when you don't using NoBuffering! You type, and getLine consumes:

first input[enter]

然后键入，getLine#2会消耗:

Then you type, and getLine #2 consumes:

second input[enter]

然后键入:

 y[enter]

但是getChar只消耗了y并保留了[enter]缓冲，这是您的第一个getLine调用读取的内容！为什么输入[enter]?因为您必须这样做，所以只需单击'y'并不会导致main循环，因为终端是行缓冲的.

But getChar only consumed the y and leaves the [enter] buffered, which your first getLine call reads! Why did you type [enter]? Because you had to, just hitting 'y' didn't cause main to loop because the terminal was line buffered.

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