Haskell IO - Output not printed until program exits

Asked May 07 '17 at 09:47

Active May 07 '17 at 10:36

Viewed 345 times

If I write a program like:

main = do
    putStrLn "Start"
    i <- getLine
    putStrLn $ "Exit " ++ i

When I run it, the output is not given until execution finishes, It just waits for input and then all the output is given at once instead of the first string being printed before the input prompt occurs.

I've tried compiling the program and running in cygwin, also tried using the runhaskell command. I'm on windows 7.

Does anyone know what the problem could be?

asked May 07 '17 at 09:47

Aaron Allen

1

Try writing `hSetBuffering stdout NoBuffering` before `putStrLn "Start` ? – Sibi May 07 '17 at 10:06
Thanks, it worked. – Aaron Allen May 07 '17 at 10:29
@duplode : I think this is a better duplicate: http://stackoverflow.com/questions/13190314/haskell-do-monad-io-happens-out-of-order – Sibi May 07 '17 at 10:35
@Sibi I added it to the list; thanks. – duplode May 07 '17 at 10:37

Haskell IO - Output not printed until program exits

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