putStr in compiled binary from GHC, Mac OS X

Question

With this file:

main = do
  putStr "Input: "
  s <- getLine
  putStr s

It does what I want in GHCi, which is to put the prompt and then allow input right there on the same line as the prompt. If I compile it and run the executable in the terminal I won't see the prompt until after I do my input. Something about the new lines. I'm using Mac OS 10.8.5, GHC 7.4.2.

Is there a terminal setting or GHC option that I need to switch to get the behavior I want from the executable?

Answer 1

You need to use hSetBuffering from System.IO

main = do
    hSetBuffering stdout NoBuffering
    putStr "Input: "
    s <- getLine
    putStr s

Answer 2

For completeness: You could also do hFlush stdout to explicitly flush the partial line to file.

But yes, for your scenario, the accepted answer is almost certainly the most sensible way.