Re: [Haskell-cafe] After `readFile`, why cannot i `writeFile` ?

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)