[Haskell-cafe] hPutStrLn and hFlush

[Stepan Golosunov]

On Mon, Jan 09, 2006 at 04:57:51PM +0100, Gracjan Polak wrote:
> Hi all,
> 
> A bit strange behaviour with hPutStrLn. Consider following program:
> 
> main = do
>     handle <- openFile "output.txt" WriteMode
>     hPutStrLn handle (unlines contLines2)
>     -- hFlush houtput
>     where
>         contLines2 = flip map [1..2000] $
>               \x -> show x ++ " been there done that"
> 
> Outputs file which ends with following lines:
> 
> 1989 been there done that
> 1990 been there done that
> 1991 been there done that
> 1992 been there done that
> 199
> (END)
> 
> So the output is truncated. When I uncomment hFlush, file is fully written.
> Is this expected/documented behaviour?

This is the usual behavior when file is not closed. And example from
http://www.haskell.org/onlinereport/io.html suggests that using hClose
is necessary.