Re: [Haskell-cafe] Convert IO Int to Int

2009/6/9 Krzysztof Skrzętnicki

On Tue, Jun 9, 2009 at 16:14, Daniel Fischer wrote:

...

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

Please do! Prefer MonadRandom to explicit generator passing: http://lukepalmer.wordpress.com/2009/01/17/use-monadrandom/. Keep computations in MonadRandom, and pull them out with evalRandomIO at the last second. Luke

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