NOTE: Even the examples are correct in the H98 libraries documentation in the IO module section, they are incorrect in the H98 Report: http://www.haskell.org/onlinereport/io-13.html Scroll down, to 7.2. <snip>
when I put the same code through ghc, it waits for a command first, and then when the command has been entered it displays the prompt, which is just silly. Surely the 'do' notation was designed to sequence computations, but it obviously isn't behaving quite right here!
The problem is that stdout is buffered by default and *not flushed when you're waiting for input in stdin*, IMO it should be. IIRC this was a change that happened between the somwhere between 5.00.1 and 5.02.2. I remember suddenly all my programs not working correctly anymore...
I'd be very grateful for any suggestions as to how to fix this. thanks, One way is to *import IO* and set stdout to NoBuffering
mainLoop :: IO TRS -> IO () mainLoop t = do putStr "\n>> " hSetBuffering stdout NoBuffering -- HERE!!! (c,a) <- getCommand 0 case c of "help" -> do putStr help mainLoop t "load" -> do trs <- load a putStr "" mainLoop (return trs) "show" -> ...and so on...
You may also flush stdout every time you want using hflush. Check the haskell libraries documentation for the IO module for more info. J.A.