> (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
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