[Haskell-beginners] getChar and keyboard reading
daniel.is.fischer at web.de
Sun Jan 24 16:06:19 EST 2010
Am Sonntag 24 Januar 2010 21:49:59 schrieb Matthias Güdemann:
> I wrote a program which should read the number of key presses in a
> given time. It forks a thread which calls getChar and increases a MVar
> each time getChar suceeds. After a delay (here 2s) the MVar is read,
> its value is printed and the program exits.
> import Control.Concurrent
> increaseEveryPush mVCount = do
> _ <- getChar
> inh <- takeMVar mVCount
> putMVar mVCount (inh + 1)
> increaseEveryPush mVCount
> main = do
> x <- newMVar 0
> forkIO (increaseEveryPush x)
> threadDelay 2000000
> inh <- takeMVar x
> putStr $ "\n" ++ (show inh) ++ " times button pushed\n"
> But this does not work, as getChar does not succeed if there is no EOF
> given (^D).
No, a newline would suffice. But you could set the buffering of stdin to
main = do
hSetBuffering stdin NoBuffering
x <- newMVar 0
forkIO (increaseEveryPush x)
inh <- takeMVar x
putStr $ "\n" ++ (show inh) ++ " times button pushed\n"
26 times button pushed
It probably won't work on Windows, though.
> It normally just exits with 0 as value in the MVar. Is
> there a way toread the keyboard without having to terminate with EOF?
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