Zerigo DDNS update script in Haskell

gistfile1.hs

import Text.XML.Light
import Network.Curl
import System.IO
import System.Environment
import System.Exit

extractIP :: String -> String
extractIP xmlString =
    let
        element = parseXMLDoc xmlString >>= findElement (QName "ipv4" Nothing Nothing)
    in
      case element of
        Nothing -> "0.0.0.0"
        Just x  -> strContent x

updateUrl :: String -> String
updateUrl ipAddress = "http://update.zerigo.com/dynamic?" ++
                      "host=nyc.stackbuilders.com&ip=" ++ ipAddress ++
                      "&user=foo@bar.com&" ++
                      "password=55555555555555"

printErrorResponse :: CurlCode -> IO ()
printErrorResponse respCode = hPutStrLn stderr $ "Error: " ++ show respCode

postIP :: String -> IO ()
postIP ipAddress = do
      case ipAddress of
        "0.0.0.0" -> putStrLn "Not posting non-routable address 0.0.0.0."
        _         -> do
                     putStrLn $ "Posting " ++ ipAddress
                     (code, body) <- curlGetString (updateUrl ipAddress) []
                     case code of
                       CurlOK -> putStrLn "A OK"
                       _ -> printErrorResponse code


main :: IO ()
main = do
  (code, body) <- curlGetString "http://checkip.zerigo.com" []
  case code of
    CurlOK -> postIP $ extractIP body
    _ -> putStrLn $ "Error: " ++ show code