On Tue, Jun 9, 2009 at 16:14, Daniel Fischer<daniel.is.fisc...@web.de> wrote: > Am Dienstag 09 Juni 2009 15:57:24 schrieb Magnus Therning: >> On Tue, Jun 9, 2009 at 2:52 PM, ptrash<ptr...@web.de> wrote: >> > Hmm...it am not getting through it. I just want to generate a random >> > number and then compare it with other numbers. Something like >> > >> > r = randomRIO (1, 10) >> > if (r > 5) then... else ... >> >> You have to do it inside the IO monad, something like >> >> myFunc = do >> r <- randomRIO (1, 10 >> if r > 5 >> then ... >> else ... >> >> /M > > Or make the source of the pseudo-random numbers explicit: > > import System.Random > > function :: (RandomGen g, Random a) => g -> other args -> result > function gen whatever > | r > 5 = blah newgen something > | r < 3 = blub newgen somethingElse > | otherwise = bling > where > (r,newgen) = randomR (lo,hi) gen > > and finally, when the programme is run: > > main = do > args <- getArgs > sg <- getStdGen > foo <- thisNThat > print $ function sg foo > > If you're doing much with random generators, wrap it in a State monad.
To avoid reinventing the wheel one can use excellent package available on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/MonadRandom > The die function simulates the roll of a die, picking a number between 1 and > 6, inclusive, and returning it in the Rand monad. > Notice that this code will work with any source of random numbers g. > > die :: (RandomGen g) => Rand g Int > die = getRandomR (1,6) > > The dice function uses replicate and sequence to simulate the roll of n dice. > > dice :: (RandomGen g) => Int -> Rand g [Int] > dice n = sequence (replicate n die) > > To extract a value from the Rand monad, we can can use evalRandIO. > > main = do > values <- evalRandIO (dice 2) > putStrLn (show values) Best regards Krzysztof Skrzętnicki _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
