main :: IO ()
main = do
  (_:source:target:_) <- getArgs
  let f '0' = '1'
      f c = c
  writeFile target . map f  =<< readFile source
main :: IO ()
main = do
  (_:source:target:_) <- getArgs
  let f '0' = '1'
      f c = c
  writeFile target . map f  =<< readFile source
main = do
  (_:source:target:_) <- getArgs
  let f '0' = '1'
      f c = c
  writeFile target . map f  =<< readFile source