This is what I'd do: {-# LANGUAGE NoMonomorphismRestriction #-} module Counter where import Control.Monad.State main = runStateT procedure (0 :: Integer) >> return () incCounter = do n <- get modify (+1) return n execFile = do n <- incCounter liftIO $ putStrLn $ ("command --createfile=tempfile" ++ show n ++ ".tmp") procedure = do execFile execFile liftIO $ putStrLn "do something" execFile On Fri, Jul 22, 2011 at 3:10 AM, Davi Santos <dps.abc@gmail.com> wrote:
Hello all, I have massive (parallel if possible) system calls to an external non-deterministic program. Each time it is executed, it creates a file depending on a command line option 'opt' (input files path, for example). How can I ensure the file name will be unique? maybe with a global counter? My temporary solution have been to use a large random number: ----------- mysteriousExecution :: String -> IO () mysteriousExecution opt = do number <- rand run $ "mysterious-command " ⊕ opt ⊕ " --create-file=" ⊕ number rand = do a ← getStdRandom (randomR (1,999999999999999999999999999999999)) ∷ IO Int let r = take 20 $ randomRs ('a','z') (mkStdGen a) ∷ String return r ======== I'm trying to avoid additional parameters to 'mysteriousExecution'. I tried a counter also (to replace rand), but I don't know how could I start it inside 'mysteriousExecution'. c ∷ IO Counter c = do r ← newIORef 0 -- start return (do modifyIORef r (+1) readIORef r) If somebody says everything is wrong, ok. I understand. 18 years of imperative programming world can damage the brain. Thanks _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners