Threading & IO using haskell

[Alain De Vos]

Sometimes functional is too functional. But haskell has also nice things.

So here a program which :
- Starts a thread reading a line from keyboard
- Starts a thread writing a line but waits on the reading thread
- And which waits on writing thread to end the program.

test.hs

import Control.Concurrent (forkIO, newChan, readChan, writeChan, Chan)

readerThread :: Chan String -> IO ()
readerThread msgChan = do
    putStrLn "Reader: Please enter a line of text:"
    line <- getLine
    writeChan msgChan line

writerThread :: Chan String -> Chan () -> IO ()
writerThread msgChan doneChan = do
    line <- readChan msgChan
    putStrLn $ "Writer received: " ++ line
    writeChan doneChan ()

main :: IO ()
main = do
    msgChan  <- newChan -- For passing the String from reader to writer
    doneChan <- newChan -- For passing a termination signal from writer to main
    _ <- forkIO (readerThread msgChan)
    _ <- forkIO (writerThread msgChan doneChan)
    _ <- readChan doneChan
    putStrLn "Main thread: Writer has finished. Exiting program."

Thats all folks!!!