相关疑难解决方法(0)

鉴于以下计划,我遇到了与monad打交道的问题.

module Main 
where
import System.Environment
import System.Directory
import System.IO
import Text.CSV

--------------------------------------------------

exister :: String -> IO Bool
exister path = do
  fileexist <- doesFileExist path 
  direxist  <- doesDirectoryExist path
  return (fileexist || direxist )

--------------------------------------------------
slurp :: String -> IO String 
slurp path = do
  withFile path ReadMode (\handle -> do
                             contents <- hGetContents handle
                             last contents `seq` return contents )
--------------------------------------------------    
main :: IO ()
main = do
  [csv_filename] <- getArgs
  putStrLn (show csv_filename)
  csv_raw <- slurp …