Christopher Done wrote:
betterStdGen :: IO StdGen
Here's what I have been using. It's a bit more complete. Of course, you can always use mkStdGen with it to get one of those if you want. (Yes, I often do that. StdGen is much maligned, but it's pretty good at what it's designed for.) Regards, Yitz module DevRandom where import System.IO import System.IO.Error import Foreign.Marshal.Alloc import Foreign.Storable import Foreign.Ptr data BlockingMode = Blocking | NonBlocking deriving (Eq, Show) -- Read data from the system random device. -- Return Nothing if there is currently not -- enough entropy in the system random device. devRandom :: Storable a => IO (Maybe a) devRandom = readDev "/dev/random" NonBlocking -- Read data from the system random device. -- If necessary, wait until there is -- enough entropy in the system random device. devRandomWait :: Storable a => IO a devRandomWait = readDev dev Blocking >>= maybe (devRandomError dev) return where dev = "/dev/random" -- Read data from the system random device. -- If there is currently not enough entropy -- in the system random device, use a lower -- quality source of randomness instead. devURandom :: Storable a => IO a devURandom = readDev dev NonBlocking >>= maybe (devRandomError dev) return where dev = "/dev/urandom" readDev :: Storable a => FilePath -> BlockingMode -> IO (Maybe a) readDev dev mode = do h <- openFile dev ReadMode hSetBuffering h NoBuffering alloca $ getMaybe h undefined where getMaybe :: Storable a => Handle -> a -> Ptr a -> IO (Maybe a) getMaybe h undef ptr = do let size = sizeOf undef n <- case mode of Blocking -> hGetBuf h ptr size NonBlocking -> hGetBufNonBlocking h ptr size if n < size then return Nothing else fmap Just $ peek ptr devRandomError :: FilePath -> IO a devRandomError p = ioError $ mkIOError illegalOperationErrorType "Unable to read from the system random device" Nothing (Just p)