Re: [Haskell-beginners] very impure [global] counter

22 Jul 2011

      I may misunderstand the issue, but why not using:

System.IO.Temp.openTempFile

and then use the returned FilePath?

This should give unique names even for multiple runs of the controlling 
program.

On 22.07.2011 11:46, David McBride wrote:
...
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  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
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Re: [Haskell-beginners] very impure [global] counter

Thomas