Cale Gibbard wrote:
You shouldn't have to flush output manually. Which implementation are you using? Try importing System.IO and doing: hGetBuffering stdout >>= print and see what gets printed. It should be "NoBuffering".
The buffering for stdout should be LineBuffering if stdout is a terminal and BlockBuffering otherwise. The buffering for stderr should always be NoBuffering.
It's actually not, if you're starting your program from ghci, which is what confused me. From GHCi, you get NoBuffering on stdout, and LineBuffering on stdin, which is sane for interactive programs. Why anyone would want LineBuffering as default on stdout is somewhat mysterious to me.
Because most programs output entire lines, and the implementation of
Haskell's putStr etc sucks when using NoBuffering (one write() per
character).
C follows the same rules (stdin/stdout use line buffering for
terminals, block buffering otherwise, stderr is always unbuffered),
even though C's puts(), printf() etc behave a lot better with
unbuffered streams (they pass either whole strings or large chunks to
write() rather than individual characters).
--
Glynn Clements