(moderator, can you please include this mail at the bottom of my previous mail?)
PS: I think the next example shows pretty well what goes wrong when you're not closing the read-handle:
------- test = do writeFile' "123.txt" "blaat"
appendFile' "123.txt" " 1" z <- readFile' "123.txt"
appendFile' "123.txt" " 2" s <- readFile' "123.txt" appendFile' "123.txt" " 3" t <- readFile' "123.txt" putStr ("\n\n") putStr (z ++ "\n" ++ s ++ "\n" ++ t)
-------
Instead of "blaat 1 blaat 1 2 blaat 1 2 3"
three lines of "blaat 1 2 3" are outputted.
Note that on a conforming Haskell 98 system, the above program (with the primes deleted) will fail. For example, GHC responds: Fail: resource busy Action: openFile Reason: file is locked File: 123.txt This is because Haskell 98 specifies that the IO system should implement multiple-reader/single-writer locks on a per-file basis. Cheers, Simon