Hello, everyone. Thank you so much to previous great answer! Now, I don't know how can I fix this. The error is, Haskell>ghc --make Temp.hs -o Temp.exe [1 of 1] Compiling Main ( Temp.hs, Temp.o ) Temp.hs:19:27: Not in scope: `inpStr' The code is, import System.IO import System.Random sentenceAry = [] main :: IO () main = do inh <- openFile "c:\\Documents and Settings\\shaegis\\inputFile.txt" ReadMode outh <- openFile "c:\\Documents and Settings\\shaegis\\outputFile.txt" WriteMode mainloop inh outh hClose inh hClose outh mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if ineof then do hPutStrLn outh inpStr return () else do inpStr <- hGetLine inh let sentenceAry = inpStr : [] mainloop inh outh I'm try to change like below, but I failed. mainloop :: Handle -> Handle -> IO () mainloop inh outh = do ineof <- hIsEOF inh if not ineof then do inpStr <- hGetLine inh let sentenceAry = inpStr : [] mainloop inh outh else do hPutStrLn outh inpStr return () I wonder why... Thank you. Sincerely, Sok Chang