problems with working with Handles

[Niels Reyngoud]

Hello,

We're two students from the department of computer science at the 
University of  Utrecht (the Netherlands), and we're havind some severe 
difficulties in working
with file handles in Haskell. Consider for example the following program:

main = do --let inputfile  = "input.txt" 
      let inputtext  = "testit"
      let outputfile = "output.txt"
      writeFile outputfile ""
      handle2 <- openFileEx outputfile (BinaryMode WriteMode)
      hPutStr handle2 (inputtext ++ " extra")
     
      handle3      <- openFileEx outputfile (BinaryMode ReadMode)
      inputtext2   <- hGetContents handle3
      handle4 <- openFileEx outputfile (BinaryMode WriteMode)
      hPutStr handle4 (inputtext ++ " extra2")


The text which should be in the outputfile is "testit extra extra2", 
instead "testit extra2" is written in.

Another strange problem is with the following program:

-------------
main = do putStr "Give inputfile for use of Super encoding\n"
      inputfile <- getLine     
          handle <- openFileEx inputfile (BinaryMode ReadMode)
          text  <- hGetContents handle
      putStr "Give outputfile for use of Super encoding\n"
      outputfile <- getLine
      encode text outputfile

encode :: String -> String -> IO()
encode text outputfile = do outputhandle <- openFileEx outputfile 
(BinaryMode WriteMode)
                            bwt (runlengthEncode text) outputhandle
                bwthandle <- openFileEx outputfile (BinaryMode ReadMode)
                bwttext   <- hGetContents bwthandle
                tracer' bwttext
                mtfhandle <- openFileEx outputfile (BinaryMode WriteMode)
                hPutStr mtfhandle (arithmeticEncode (runlengthEncode 
(movetofront bwttext)))
               

tracer' :: String -> IO()
tracer' x = writeFile "temp.txt" x

-------------
This only seems to work when we're calling 'tracer' ', so if we're 
actually doing somewhing with "bwttext" before using it...

Also, we're wondering when you can close a handle. Personally we thought 
you could close it if you are "done" with it, yet if you've captured the 
contents of a file like this:

handle <- openFileEx inputfile (BinaryMode ReadMe)
text <- hGetContents handle
hClose handle
putStr text

no text appears on the screen; "text" seems empty.

We're testing on a Windows machine by the way.

Regards,
Niels Reyngoud and Richard Nieuwenhuis