# random: Pseudo-random number generation

[ bsd3, library, system ] [ Propose Tags ]

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

As an example, here is how you can simulate rolls of a six-sided die using System.Random.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 System.Random.Stateful.uniformM and System.Random.Stateful.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 System.Random.Stateful.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 System.Random.Stateful.runStateGen_ is used here to lift the pure pseudo-random number generator pureGen into the System.Random.Stateful.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.

Versions [RSS] [faq] 1.0.0.0, 1.0.0.1, 1.0.0.2, 1.0.0.3, 1.0.1.0, 1.0.1.1, 1.0.1.3, 1.1, 1.2.0, 1.2.1 (info) CHANGELOG.md base (>=4.8 && <5), bytestring (>=0.10.4 && <0.12), deepseq (>=1.1 && <2), ghc-byteorder, mtl (==2.2.*), splitmix (==0.1.*), transformers [details] BSD-3-Clause core-libraries-committee@haskell.org System https://github.com/haskell/random/issues head: git clone https://github.com/haskell/random.git by lehins at 2021-09-19T21:16:09Z Arch:1.2.1, Debian:1.1, Fedora:1.2.0, FreeBSD:1.1, LTSHaskell:1.2.0, NixOS:1.2.0, Stackage:1.2.1, openSUSE:1.1 413618 total (2308 in the last 30 days) 2.5 (votes: 4) [estimated by Bayesian average] λ λ λ Docs available Last success reported on 2021-09-19

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## Random Number Generation

### Status

Language Github Actions Drone.io Coveralls
Github Repo Hackage Nightly LTS
random

### Description

This library provides a basic interface for (splittable) pseudo-random number generators.

The API documentation can be found here:

An older version of this library is included with GHC in the haskell98 package. This newer version is included in the Haskell Platform.

Please report bugs in the GitHub issue tracker (no longer in the GHC trac).