[Haskell-cafe] Conversion from string to array

[Neil Davies]

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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