[Haskell] COM port IO on a Windows machine?

[Steve Carlisle]

Again, sorry this doesn't help too much on Windows, but your test1 runs 
just fine on Mac OSX in both GHC and Hugs98.  I changed the device to suit, 
but otherwise it was unchanged.

hIsWritable reports True on Hugs98 but False on GHCi, curiously.


On Windows, in Hugs98, I get a different error message

Program error: <handle>: IO.hGetChar: permission denied

but this changed to the same error message as yours when I started 
experimenting with the mode setting.  Nothing I've tried seems to allow 
this to work.  If you don't send first and only read, then it works fine.

On Windows GHCi, I can only agree with your findings.



At 13:32 23/03/2004 +1030, Peter Pudney wrote:
>Thanks, Steve and Axel, for your help. I have got serial port IO working, but
>the solution is a bit ugly. My solution (below) works on Windows 2000, 
>Hugs Nov
>2003. It does not work with Windows 2000, GHI 5.04.2. Later tonight I will try
>it on Windows ME with the latest versions of GHC and Hugs.
>
>The aim is to send a '?' character to a device on the serial port "COM2:". The
>device waits for a button to be pressed, then sends back a character. The test
>script then has to read this character from the serial port and display it.
>
>I first tried opening "COM2:" in ReadWriteMode, but this did not work with
>either GHCi or Hugs. For my second attempt, I open and close the file "COM2:"
>in the appropriate mode each time I send or receive a string. Its ugly, but it
>works.
>
>I am still interested in hearing from anyone who can get this working nicely
>with GHC.
>
>My code is below.
>
>
>
> >  module SerialIO where
>
> >  import IO
>
>
>Attempt 1:
>
> >  test1 :: IO ()
> >  test1
> >    = do
> >        com2 <- openFile "COM2:" ReadWriteMode
> >        hSetBuffering com2 NoBuffering
> >        isOpen <- hIsOpen com2
> >        isWritable <- hIsWritable com2
> >        isReadable <- hIsReadable com2
> >        putStrLn $ "hIsOpen = " ++ show isOpen
> >        putStrLn $ "hIsWritable = " ++ show isWritable
> >        putStrLn $ "hIsReadable = " ++ show isReadable
> >        putStrLn "About to send..."
> >        hPutStrLn com2 "?"
> >        putStrLn "Reading..."
> >        c <- hGetChar com2
> >        putStrLn [c]
> >        putStrLn "Hoorah!"
> >        hClose com2
>
>Hugs Nov 2003 sends the character OK, but then...
>
>Reading...
>
>Program error: <handle>: IO.hGetChar: does not exist (file does not exist)
>
>
>GHCI 5.04.2 gives hIsWritable = False, then "No such file or directory" 
>when it
>attempts to hPutChar.
>
>
>
>Attempt 2: open and close COM2 for each transmission
>
> >  test2 :: IO ()
> >  test2
> >    = do
> >        sendChar '?'
> >        c <- receiveChar
> >        putStrLn [c]
>
> >  sendChar :: Char -> IO ()
> >  sendChar c
> >    = do
> >        com2 <- openFile "COM2:" WriteMode
> >        hSetBuffering com2 NoBuffering
> >        hPutChar com2 '?'
> >        hClose com2
>
> >  receiveChar :: IO Char
> >  receiveChar
> >    = do
> >        com2 <- openFile "COM2:" ReadMode
> >        hSetBuffering com2 NoBuffering
> >        c <- hGetChar com2
> >        return c
>
>
>GHCI fails as before, but Hugs works.