random-1.2.1.1: Pseudo-random number generation

This package provides basic pseudo-random number generation, including the ability to split random number generators.

System.Random : pure pseudo-random number interface

In pure code, use uniform and uniformR from System.Random to generate pseudo-random numbers with a pure pseudo-random number generator like StdGen .

As an example, here is how you can simulate rolls of a six-sided die using uniformR :

>>> let roll = uniformR (1, 6)        :: RandomGen g => g -> (Word, g)
>>> let rolls = unfoldr (Just . roll) :: RandomGen g => g -> [Word]
>>> let pureGen = mkStdGen 42
>>> take 10 (rolls pureGen)           :: [Word]
[1,1,3,2,4,5,3,4,6,2]

See System.Random for more details.

System.Random.Stateful : monadic pseudo-random number interface

In monadic code, use uniformM and uniformRM from System.Random.Stateful to generate pseudo-random numbers with a monadic pseudo-random number generator, or using a monadic adapter.

As an example, here is how you can simulate rolls of a six-sided die using uniformRM :

>>> let rollM = uniformRM (1, 6)                 :: StatefulGen g m => g -> m Word
>>> let pureGen = mkStdGen 42
>>> runStateGen_ pureGen (replicateM 10 . rollM) :: [Word]
[1,1,3,2,4,5,3,4,6,2]

The monadic adapter runStateGen_ is used here to lift the pure pseudo-random number generator pureGen into the StatefulGen context.

The monadic interface can also be used with existing monadic pseudo-random number generators. In this example, we use the one provided in the mwc-random package:

>>> import System.Random.MWC as MWC
>>> let rollM = uniformRM (1, 6)       :: StatefulGen g m => g -> m Word
>>> monadicGen <- MWC.create
>>> replicateM 10 (rollM monadicGen) :: IO [Word]
[2,3,6,6,4,4,3,1,5,4]

See System.Random.Stateful for more details.