Re: [Haskell-cafe] Cleaner way to write code and handle errors?

28 Jun 2011


      On 28 June 2011 18:08, John Ky  wrote:
...
Hi all,
I'm practising my Haskell by writing a simple TCP echo server and finding
that getting my program control to be succinct is rather tricky.  In
particular, I have return () everywhere, my error handling is verbose and
I'm not entirely sure my recursion is the cleanest way syntactically to get
my loops going and terminating.
I must be doing something obviously un-Haskell-like.
Any suggestions on how I can improve my code?  Code below.
Cheers,
-John
import Control.Concurrent
import Control.Exception
import Control.Monad
import Network
import System.IO
import System.IO.Error (isEOFError)
main = withSocketsDo $ do
  sListen <- listenOn (PortNumber 8000)
  putStrLn "Listening on Port 8000"
  forkIO $ forever $ do
    (sSession, hostname, port) <- accept sListen
    putStrLn ("Connected to " ++ hostname ++ ":" ++ (show port))
    let processLine = forkIO $ do
        lineResult <- try (hGetLine sSession)
        case lineResult of
          Right line -> do
            putStrLn line
            processLine
            return ()
          Left e ->
            if isEOFError e
                then putStrLn (show e)
                else do
                  ioError e
                  return ()
        return ()
    processLine
    return()
  line <- getLine
  return ()
I don't think you need all those return () everywhere... And at the
end, why do you do "line <- getLine" when you don't use the result?

-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic@gmail.com
IvanMiljenovic.wordpress.com