为什么 Haskell 不能正确排序这些 IO 操作?

问题描述

我的一个朋友问我为什么要学习 Haskell.为了展示 Haskell 的强大功能，我编写了一个显示质数列表的小程序:

A friend of mine asked me why was I learning Haskell. To demonstrate the power of Haskell I wrote a small program which displayed a list of prime numbers:

main = do
    putStr "Enter the number of prime numbers to display: "
    number <- fmap read getLine :: IO Int
    print . take number . filter isPrime $ [2..]

isPrime :: Integer -> Bool
isPrime n = not . any ((== 0) . mod n) $ [2..floor . sqrt . fromInteger $ n]

该程序按预期工作，但存在轻微异常.它在从用户那里获取输入号码后打印提示消息，结果如下:

The program works as expected save a minor anomaly. It prints the prompt message after taking an input number from the user resulting in an output like:

12
Enter the number of prime numbers to display: [2,3,5,7,11,13,17,19,23,29,31,37]

为什么 Haskell 没有正确排序 IO 操作?我哪里出错了?

Why is Haskell not sequencing the IO actions correctly? Where am I going wrong?

推荐答案

这看起来更像是一个缓冲而不是排序问题.你在什么平台?您是否尝试过强制无缓冲输出?

This looks more like a buffering than a sequencing problem. What platform are you on? Have you tried forcing unbuffered output?

hSetBuffering stdout NoBuffering -- from System.IO

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