Re: [Haskell-cafe] Conversion from string to array

6 Jun 2009

      Look at Data.Binary (binary package)

It will marshall and unmarshall data types for you. If you don't like  
its binary encoding you can dive in there and use the same principles

Cheers

Neil

On 6 Jun 2009, at 07:13, John Ky wrote:
...
Hi Haskell Cafe,
I'm trying to send stuff over UDP.  To do that, I've written a test  
program that sends strings across.  That was fine, but I wanted to  
send binary data too.  So I tried that only to find I am having  
difficulty putting together some binary data.  For examples take the  
fromHex function in the following code.
It is supposed to convert from a Hexadecimal string to a list of  
bytes, but I am having trouble coercing the integer types to the  
size I want.
Is this the right way to do it?
Cheers,
-John
...
import Data.Bits
 import Data.Char
 import Data.Word
 import System.Environment
 import XStream.Tsmr.Client
...
data CmdLineOptions = CmdLineOptions
    { optionHelp :: Bool
    , optionVersion :: Bool
    , optionPort :: String
    , optionMessage :: String
    , optionInvalids :: [String]
    }
    deriving (Eq, Show)
...
initCmdLineOptions = CmdLineOptions
    { optionHelp = False
    , optionVersion = False
    , optionPort = "1234"
    , optionMessage = ""
    }
...
parseArgs :: [String] -> CmdLineOptions
 parseArgs [] = initCmdLineOptions
 parseArgs ("--port":port:xs) = (parseArgs xs) { optionPort = port }
 parseArgs ("--help":xs) = (parseArgs xs) { optionHelp = True }
 parseArgs ("--version":xs) = (parseArgs xs) { optionVersion =  
True }
 parseArgs (('-':opt):xs) = let option = (parseArgs xs) in
    option { optionInvalids = ('-':opt):optionInvalids option }
 parseArgs (message:xs) = (parseArgs xs) { optionMessage = message }
...
printUsage = do
    putStrLn "Usage: udp-server.lhs [options] <message>"
    putStrLn ""
    putStrLn "Options:"
    putStrLn "  --help      Get help information."
    putStrLn "  --vesion    Get version information."
    putStrLn "  --port n    The port number to listen on."
    putStrLn ""
    putStrLn "Message:"
    putStrLn "  The message to send."
    putStrLn ""
...
printVersion = do
    putStrLn "Version."
...
fromHex :: String -> [Word8]
 fromHex [] = []
 fromHex (u:l:xs) = (hexU .|. hexL):fromHex xs
    where
       hexU = (fromInteger $ hexValue u) :: Word8
       hexL = (fromInteger $ hexValue l) :: Int
       hexValue c
          | '0' <= c && c <= '9' = ord c - ord '0'
          | 'a' <= c && c <= 'z' = ord c - ord 'a' + 10
...
run port message = do
    h <- openlog "localhost" port "udp-client.lhs"
    syslog h (fromHex message)
...
main = do
    args <- getArgs
    let options = parseArgs args
    let port = optionPort options
    let message = optionMessage options
    if optionHelp options
       then printUsage
       else if optionVersion options
          then printVersion
          else do
             putStrLn ("Starting UDP listener on port: " ++ port)
             run port message
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Re: [Haskell-cafe] Conversion from string to array

Neil Davies