Question

所以我刚刚创建了一个程序，要求输入一个 n ，并显示 n 斐波纳契数列的术语：

import Control.Monad (forever)

main = forever $ do
    putStrLn ""
    putStr "Which Fibonacci sequence number do you need? "
    number <- readLn :: IO Int
    putStrLn $ "The Fibonacci number you wanted is " ++ (show $ fib number) ++ "."
    putStrLn ""
    where  fib :: Int -> Integer
           fib number = fibs !! number
           fibs = 0 : 1 : zipWith (+) fibs (tail fibs)

当我在GHCi或runhaskell中运行程序时，它执行正常;也就是说，要求我输入一个数字，允许我在同一行输入它并在另一行返回一个数字：

Gallifreian@Gallifrey:~/Haskell$ ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Prelude> :l Fib.hs
[1 of 1] Compiling Main             ( Fib.hs, interpreted )
Ok, modules loaded: Main.
*Main> main

Which Fibonacci sequence number do you need? 4
The Fibonacci number you wanted is 3.

但是，当我运行已编译的程序时，它会返回：

Gallifreian@Gallifrey:~/Haskell$ ./Fib

4
Which Fibonacci sequence number do you need? The Fibonacci number you wanted is 3.

予。即等待我输入一个数字，然后在一行上返回所有提示。我做错了什么？有办法解决这个问题吗？

Answer 1

看起来stdout有行缓冲，这意味着对putStr的调用只将输出存储在缓冲区中，直到调用putStrLn才会输出。您可以通过使用putStrLn来提示输出或在stdout上禁用缓冲来修复输出。

Haskell控制台程序输出顺序错误

1 个答案: