After `readFile`, why cannot i `writeFile` ?

zaxis

5 Jun 2010 5 Jun '10

10:39 p.m.

hitSSQ :: String -> [Int] -> IO () hitSSQ no hitNum = do let newNum = unwords $ [no] ++ map (\n -> show n) hitNum hitNums <- fmap lines $ readFile "test.txt" writeFile "test.txt" $ unlines $ hitNums ++ [newNum] *** Exception: test.txt: openFile: resource busy (file is locked) Sincerely! ----- e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/After-%60readFile%60%2C-why-cannot-i-%60writeFile%60--... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Ivan Lazar Miljenovic

7 Jun 7 Jun

6:53 p.m.

zaxis writes:

...

hitSSQ :: String -> [Int] -> IO () hitSSQ no hitNum = do let newNum = unwords $ [no] ++ map (\n -> show n) hitNum hitNums <- fmap lines $ readFile "test.txt" writeFile "test.txt" $ unlines $ hitNums ++ [newNum]

*** Exception: test.txt: openFile: resource busy (file is locked)

You're currently reading the file; finish reading it and close it before you write over it (or else use WriteRead mode or whatever it's called and call openFile explicitly rather than using readFile and writeFile). -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com

Bill Atkins

7:18 p.m.

readFile reads the file lazily so it isn't closed until the entire contents have been consumed. Try System.IO.Strict.readFile, which will read the entire file at once. zaxis writes:

...

hitSSQ :: String -> [Int] -> IO () hitSSQ no hitNum = do let newNum = unwords $ [no] ++ map (\n -> show n) hitNum hitNums <- fmap lines $ readFile "test.txt" writeFile "test.txt" $ unlines $ hitNums ++ [newNum]

*** Exception: test.txt: openFile: resource busy (file is locked)

zaxis

8:37 p.m.

Bill Atkins-6 wrote:

...

readFile reads the file lazily so it isn't closed until the entire contents have been consumed.

Try System.IO.Strict.readFile, which will read the entire file at once. Yes, and i can use appendFile too.

appendFile "ssqHitNum.txt" $ unwords $ [no] ++ map (\n -> show n) hitNum ++ ["\n"]

zaxis writes:

...
hitSSQ :: String -> [Int] -> IO () hitSSQ no hitNum = do let newNum = unwords $ [no] ++ map (\n -> show n) hitNum hitNums <- fmap lines $ readFile "test.txt" writeFile "test.txt" $ unlines $ hitNums ++ [newNum]

*** Exception: test.txt: openFile: resource busy (file is locked)

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----- e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/After-%60readFile%60%2C-why-cannot-i-%60writeFile%60--... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

Bill Atkins

9:34 p.m.

BTW, "\n -> show n" is equivalent to "show" . On Monday Jun 7, 2010, at 8:37 PM, zaxis wrote:

...

...
Yes, and i can use appendFile too.

appendFile "ssqHitNum.txt" $ unwords $ [no] ++ map (\n -> show n) hitNum ++ ["\n"]

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Bill Atkins
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zaxis