Haskell ByteString Samle

copy.hs

import System.Environment
import System.Directory	-- openTempFile , removeFile
import System.IO	
import Control.Exception -- bracketOnError
import qualified Data.ByteString.Lazy as B
{-
This code is referenced from "Learn You a Haskell for Great Good!!"
-}

main = do
     ( filename1:filename2:_) <- getArgs
     copy filename1 filename2

copy :: String -> String -> IO ()
copy source dest = do
     contents <- B.readFile source
     bracketOnError (openTempFile "." "temp")
     		    (\(tempPath, tempHandle) -> do
		    	    	      hClose tempHandle
				      removeFile tempPath)
     		    (\(tempPath,tempHandle) -> do
		    		     B.hPutStr tempHandle contents
				     hClose tempHandle
				     renameFile tempPath dest
				     )