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.