Random

The Random library deals with the common task of pseudo-random number generation. The library makes it possible to generate repeatable results, by starting with a specified initial random number generator; or to get different results on each run by using the system-initialised generator, or by supplying a seed from some other source.

module Random (
RandomGen(next, split),
StdGen, mkStdGen,
Random( random,   randomR, 
randoms,  randomRs,
randomIO, randomRIO ),
getStdRandom, getStdGen, setStdGen, newStdGen
  ) where

---------------- The RandomGen class ------------------------

class RandomGen g where
  next  :: g  -> (Int, g)
  split :: g -> (g, g)

---------------- A standard instance of RandomGen -----------
data StdGen = ... -- Abstract

instance RandomGen StdGen where ...
instance Read     StdGen where ...
instance Show     StdGen where ...

mkStdGen :: Int -> StdGen

---------------- The Random class ---------------------------
class Random a where
   randomR :: RandomGen g => (a, a) -> g -> (a, g)
   random  :: RandomGen g => g -> (a, g)

   randomRs :: RandomGen g => (a, a) -> g -> [a]
   randoms  :: RandomGen g => g -> [a]

   randomRIO :: (a,a) -> IO a
   randomIO  :: IO a

instance Random Int     where ...
instance Random Integer where ...
instance Random Float   where ...
instance Random Double  where ...
instance Random Bool    where ...
instance Random Char    where ...

---------------- The global random generator ----------------
newStdGen    :: IO StdGen
setStdGen    :: StdGen -> IO ()
getStdGen    :: IO StdGen
getStdRandom :: (StdGen -> (a, StdGen)) -> IO a


The Random