Re: [Haskell-beginners] File I/O: reading from, writing to, same file in one function

If you're still wedded to your notion (I strongly urge you to use the proper way with temp file and renaming, even making it a function if you need to repeat this several times) : readModifyWrite fileName modify = do contents <- readFile fileName evaluate (length contents) -- ensure that contents is evaluated and the handle closed writeFile fileName (modify contents) This should work (but may consume a fair bit of memory, you should probably use Text or ByteString anyway and use the proper way instead). -- Jedaï