- acquireLock :: IO Fd
- acquireLock
- = do fd <- openFd revFile ReadWrite (Just stdFileMode) defaultFileFlags
- waitToSetLock fd (WriteLock, AbsoluteSeek, 0, 0)
- return fd
-
- releaseLock :: Fd -> IO ()
- releaseLock fd
- = setLock fd (Unlock, AbsoluteSeek, 0, 0)
-
- update :: Fd -> IO ()
- update fd
- = do fdSeek fd AbsoluteSeek 0
- size <- return . fromIntegral . fileSize =<< getFdStatus fd
- (revStr, gotSize) <- fdRead fd size
- when (size /= gotSize) $ fail ("read " ++ show gotSize ++
- " bytes but expected " ++ show size ++ " bytes")
-
- let rev = case revStr of
- "" -> 0
- _ -> read revStr
-
- rev' <- f rev
-
- let revStr' = show rev' ++ "\n"
- size' = fromIntegral $ length revStr'
-
- fdSeek fd AbsoluteSeek 0
- setFdSize fd 0
- wroteSize <- fdWrite fd revStr'
- when (size' /= wroteSize) $ fail ("wrote " ++ show wroteSize ++
- " bytes but expected " ++ show size' ++ " bytes")
+ update :: Handle -> IO ()
+ update h = do eof <- hIsEOF h
+ rev <- if eof then
+ return 0
+ else
+ hGetLine h >>= return . read
+ rev' <- f rev
+ hSeek h AbsoluteSeek 0
+ hSetFileSize h 0
+ hPutStrLn h (show rev')