example.hs

data ReadState = None | Input | Output

split :: (Char -> Bool) -> String -> [String]
split f s = let (prefix, rest) = break s in
  case rest of
    []     -> [prefix]
    [c]    -> [prefix]
    (c:cs) -> prefix : (split f cs)

main :: IO ()
main = do
  handle <- openFile "nome.do.arquivo"
  contents <- hGetContents handle
  processLines None (lines contents)

processLines :: [String] -> ReadState -> IO ()
processLines []           _     = pure ()
processLines (line:rest)  state =
  let [code, value] = split (== '|') line
      newState      = processLine state code value in
    processLines rest newState

processLine :: ReadState -> String -> String -> ReadState
processLine _ "C100" status
  | status == "entrada" = Input
  | status == "saida"   = Output
  | otherwise           = error "Linha inválida!"
processLine _ _ _ = ... -- tratar os outros casos