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]

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]

The monadic adapter System.Random.Stateful.runGenState_ 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]

See System.Random.Stateful for more details.

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Versions [RSS],,,,,,, 1.1, 1.2.0, 1.2.1, (info)
Change log CHANGELOG.md
Dependencies base (>=4.8 && <4.16), bytestring (>=0.10.4 && <0.12), deepseq (>=1.1 && <2), mtl (>=2.2 && <2.3), splitmix (>=0.1 && <0.2), transformers [details]
License BSD-3-Clause
Maintainer core-libraries-committee@haskell.org
Revised Revision 6 made by Bodigrim at 2021-07-11T22:38:05Z
Category System
Bug tracker https://github.com/haskell/random/issues
Source repo head: git clone https://github.com/haskell/random.git
Uploaded by lehins at 2020-06-23T13:25:29Z
Distributions Arch:, Debian:1.1, Fedora:, FreeBSD:1.1, LTSHaskell:, NixOS:, Stackage:, openSUSE:
Reverse Dependencies 1002 direct, 9287 indirect [details]
Downloads 429283 total (464 in the last 30 days)
Rating 2.5 (votes: 5) [estimated by Bayesian average]
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Status Docs available [build log]
Last success reported on 2020-06-23 [all 1 reports]

Readme for random-1.2.0

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The Haskell Standard Library

Random Number Generation


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Package Hackage Nightly LTS
random Hackage Nightly Nightly


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).