Copyright	(c) The University of Glasgow 2001
License	BSD-style (see the file LICENSE in the 'random' repository)
Maintainer	libraries@haskell.org
Stability	stable
Safe Haskell	Trustworthy
Language	Haskell2010

System.Random

Contents

Introduction
Usage
Pure number generator interface
- Standard pseudo-random number generator
- Global standard pseudo-random number generator
Compatibility and reproducibility
- Backwards compatibility and deprecations
- Reproducibility
Notes for pseudo-random number generator implementors
- How to implement RandomGen
References

Description

This library deals with the common task of pseudo-random number generation.

Synopsis

class RandomGen g where
- next :: g -> (Int, g)
- genWord8 :: g -> (Word8, g)
- genWord16 :: g -> (Word16, g)
- genWord32 :: g -> (Word32, g)
- genWord64 :: g -> (Word64, g)
- genWord32R :: Word32 -> g -> (Word32, g)
- genWord64R :: Word64 -> g -> (Word64, g)
- genShortByteString :: Int -> g -> (ShortByteString, g)
- genRange :: g -> (Int, Int)
- split :: g -> (g, g)
uniform :: (RandomGen g, Uniform a) => g -> (a, g)
uniformR :: (RandomGen g, UniformRange a) => (a, a) -> g -> (a, g)
genByteString :: RandomGen g => Int -> g -> (ByteString, g)
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]
class Uniform a
class UniformRange a
data StdGen
mkStdGen :: Int -> StdGen
getStdRandom :: MonadIO m => (StdGen -> (a, StdGen)) -> m a
getStdGen :: MonadIO m => m StdGen
setStdGen :: MonadIO m => StdGen -> m ()
newStdGen :: MonadIO m => m StdGen
randomIO :: (Random a, MonadIO m) => m a
randomRIO :: (Random a, MonadIO m) => (a, a) -> m a

Introduction

This module provides type classes and instances for the following concepts:

Pure pseudo-random number generators: RandomGen is an interface to pure pseudo-random number generators.
StdGen, the standard pseudo-random number generator provided in this library, is an instance of RandomGen. It uses the SplitMix implementation provided by the splitmix package. Programmers may, of course, supply their own instances of RandomGen.

Usage

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

>>> :{
let rolls :: RandomGen g => Int -> g -> [Word]
    rolls n = take n . unfoldr (Just . uniformR (1, 6))
    pureGen = mkStdGen 137
in
    rolls 10 pureGen :: [Word]
:}
[4,2,6,1,6,6,5,1,1,5]

To run use a monadic pseudo-random computation in pure code with a pure pseudo-random number generator, use runGenState and its variants.

>>> :{
let rollsM :: StatefulGen g m => Int -> g -> m [Word]
    rollsM n = replicateM n . uniformRM (1, 6)
    pureGen = mkStdGen 137
in
    runStateGen_ pureGen (rollsM 10) :: [Word]
:}
[4,2,6,1,6,6,5,1,1,5]

Pure number generator interface

Pseudo-random number generators come in two flavours: pure and monadic.

RandomGen: pure pseudo-random number generators: These generators produce a new pseudo-random value together with a new instance of the pseudo-random number generator.
Pure pseudo-random number generators should implement split if they are splittable, that is, if there is an efficient method to turn one generator into two. The pseudo-random numbers produced by the two resulting generators should not be correlated. See [1] for some background on splittable pseudo-random generators.
StatefulGen: monadic pseudo-random number generators: See System.Random.Stateful module

class RandomGen g where #

RandomGen is an interface to pure pseudo-random number generators.

StdGen is the standard RandomGen instance provided by this library.

Minimal complete definition

split, (genWord32 | genWord64 | next, genRange)

Methods

next :: g -> (Int, g) #

Deprecated: No longer used

Returns an Int that is uniformly distributed over the range returned by genRange (including both end points), and a new generator. Using next is inefficient as all operations go via Integer. See here for more details. It is thus deprecated.

genWord8 :: g -> (Word8, g) #

Returns a Word8 that is uniformly distributed over the entire Word8 range.

Since: 1.2.0

genWord16 :: g -> (Word16, g) #

Returns a Word16 that is uniformly distributed over the entire Word16 range.

Since: 1.2.0

genWord32 :: g -> (Word32, g) #

Returns a Word32 that is uniformly distributed over the entire Word32 range.

Since: 1.2.0

genWord64 :: g -> (Word64, g) #

Returns a Word64 that is uniformly distributed over the entire Word64 range.

Since: 1.2.0

genWord32R :: Word32 -> g -> (Word32, g) #

genWord32R upperBound g returns a Word32 that is uniformly distributed over the range [0, upperBound].

Since: 1.2.0

genWord64R :: Word64 -> g -> (Word64, g) #

genWord64R upperBound g returns a Word64 that is uniformly distributed over the range [0, upperBound].

Since: 1.2.0

genShortByteString :: Int -> g -> (ShortByteString, g) #

genShortByteString n g returns a ShortByteString of length n filled with pseudo-random bytes.

Since: 1.2.0

genRange :: g -> (Int, Int) #

Deprecated: No longer used

Yields the range of values returned by next.

It is required that:

If (a, b) = genRange g, then a < b.
genRange must not examine its argument so the value it returns is determined only by the instance of RandomGen.

The default definition spans the full range of Int.

split :: g -> (g, g) #

Returns two distinct pseudo-random number generators.

Implementations should take care to ensure that the resulting generators are not correlated. Some pseudo-random number generators are not splittable. In that case, the split implementation should fail with a descriptive error message.

Instances

Instances details

RandomGen SMGen #
Instance details Defined in System.Random.Internal Methods next :: SMGen -> (Int, SMGen) # genWord8 :: SMGen -> (Word8, SMGen) # genWord16 :: SMGen -> (Word16, SMGen) # genWord32 :: SMGen -> (Word32, SMGen) # genWord64 :: SMGen -> (Word64, SMGen) # genWord32R :: Word32 -> SMGen -> (Word32, SMGen) # genWord64R :: Word64 -> SMGen -> (Word64, SMGen) # genShortByteString :: Int -> SMGen -> (ShortByteString, SMGen) # genRange :: SMGen -> (Int, Int) # split :: SMGen -> (SMGen, SMGen) #
RandomGen SMGen #
Instance details Defined in System.Random.Internal Methods next :: SMGen -> (Int, SMGen) # genWord8 :: SMGen -> (Word8, SMGen) # genWord16 :: SMGen -> (Word16, SMGen) # genWord32 :: SMGen -> (Word32, SMGen) # genWord64 :: SMGen -> (Word64, SMGen) # genWord32R :: Word32 -> SMGen -> (Word32, SMGen) # genWord64R :: Word64 -> SMGen -> (Word64, SMGen) # genShortByteString :: Int -> SMGen -> (ShortByteString, SMGen) # genRange :: SMGen -> (Int, Int) # split :: SMGen -> (SMGen, SMGen) #
RandomGen StdGen #
Instance details Defined in System.Random.Internal Methods next :: StdGen -> (Int, StdGen) # genWord8 :: StdGen -> (Word8, StdGen) # genWord16 :: StdGen -> (Word16, StdGen) # genWord32 :: StdGen -> (Word32, StdGen) # genWord64 :: StdGen -> (Word64, StdGen) # genWord32R :: Word32 -> StdGen -> (Word32, StdGen) # genWord64R :: Word64 -> StdGen -> (Word64, StdGen) # genShortByteString :: Int -> StdGen -> (ShortByteString, StdGen) # genRange :: StdGen -> (Int, Int) # split :: StdGen -> (StdGen, StdGen) #
RandomGen g => RandomGen (StateGen g) #
Instance details Defined in System.Random.Internal Methods next :: StateGen g -> (Int, StateGen g) # genWord8 :: StateGen g -> (Word8, StateGen g) # genWord16 :: StateGen g -> (Word16, StateGen g) # genWord32 :: StateGen g -> (Word32, StateGen g) # genWord64 :: StateGen g -> (Word64, StateGen g) # genWord32R :: Word32 -> StateGen g -> (Word32, StateGen g) # genWord64R :: Word64 -> StateGen g -> (Word64, StateGen g) # genShortByteString :: Int -> StateGen g -> (ShortByteString, StateGen g) # genRange :: StateGen g -> (Int, Int) # split :: StateGen g -> (StateGen g, StateGen g) #
RandomGen g => RandomGen (STGen g) #
Instance details Defined in System.Random.Stateful Methods next :: STGen g -> (Int, STGen g) # genWord8 :: STGen g -> (Word8, STGen g) # genWord16 :: STGen g -> (Word16, STGen g) # genWord32 :: STGen g -> (Word32, STGen g) # genWord64 :: STGen g -> (Word64, STGen g) # genWord32R :: Word32 -> STGen g -> (Word32, STGen g) # genWord64R :: Word64 -> STGen g -> (Word64, STGen g) # genShortByteString :: Int -> STGen g -> (ShortByteString, STGen g) # genRange :: STGen g -> (Int, Int) # split :: STGen g -> (STGen g, STGen g) #
RandomGen g => RandomGen (IOGen g) #
Instance details Defined in System.Random.Stateful Methods next :: IOGen g -> (Int, IOGen g) # genWord8 :: IOGen g -> (Word8, IOGen g) # genWord16 :: IOGen g -> (Word16, IOGen g) # genWord32 :: IOGen g -> (Word32, IOGen g) # genWord64 :: IOGen g -> (Word64, IOGen g) # genWord32R :: Word32 -> IOGen g -> (Word32, IOGen g) # genWord64R :: Word64 -> IOGen g -> (Word64, IOGen g) # genShortByteString :: Int -> IOGen g -> (ShortByteString, IOGen g) # genRange :: IOGen g -> (Int, Int) # split :: IOGen g -> (IOGen g, IOGen g) #
RandomGen g => RandomGen (AtomicGen g) #
Instance details Defined in System.Random.Stateful Methods next :: AtomicGen g -> (Int, AtomicGen g) # genWord8 :: AtomicGen g -> (Word8, AtomicGen g) # genWord16 :: AtomicGen g -> (Word16, AtomicGen g) # genWord32 :: AtomicGen g -> (Word32, AtomicGen g) # genWord64 :: AtomicGen g -> (Word64, AtomicGen g) # genWord32R :: Word32 -> AtomicGen g -> (Word32, AtomicGen g) # genWord64R :: Word64 -> AtomicGen g -> (Word64, AtomicGen g) # genShortByteString :: Int -> AtomicGen g -> (ShortByteString, AtomicGen g) # genRange :: AtomicGen g -> (Int, Int) # split :: AtomicGen g -> (AtomicGen g, AtomicGen g) #

uniform :: (RandomGen g, Uniform a) => g -> (a, g) #

Generates a value uniformly distributed over all possible values of that type.

This is a pure version of uniformM.

Examples

Expand

>>> import System.Random
>>> let pureGen = mkStdGen 137
>>> uniform pureGen :: (Bool, StdGen)
(True,StdGen {unStdGen = SMGen 11285859549637045894 7641485672361121627})

Since: 1.2.0

uniformR :: (RandomGen g, UniformRange a) => (a, a) -> g -> (a, g) #

Generates a value uniformly distributed over the provided range, which is interpreted as inclusive in the lower and upper bound.

uniformR (1 :: Int, 4 :: Int) generates values uniformly from the set \(\{1,2,3,4\}\)
uniformR (1 :: Float, 4 :: Float) generates values uniformly from the set \(\{x\;|\;1 \le x \le 4\}\)

The following law should hold to make the function always defined:

uniformR (a, b) = uniformR (b, a)

This is a pure version of uniformRM.

Examples

Expand

>>> import System.Random
>>> let pureGen = mkStdGen 137
>>> uniformR (1 :: Int, 4 :: Int) pureGen
(4,StdGen {unStdGen = SMGen 11285859549637045894 7641485672361121627})

Since: 1.2.0

genByteString :: RandomGen g => Int -> g -> (ByteString, g) #

Generates a ByteString of the specified size using a pure pseudo-random number generator. See uniformByteString for the monadic version.

Examples

Expand

>>> import System.Random
>>> import Data.ByteString
>>> let pureGen = mkStdGen 137
>>> unpack . fst . genByteString 10 $ pureGen
[51,123,251,37,49,167,90,109,1,4]

Since: 1.2.0

class Random a where #

The class of types for which uniformly distributed values can be generated.

Random exists primarily for backwards compatibility with version 1.1 of this library. In new code, use the better specified Uniform and UniformRange instead.

Minimal complete definition

Nothing

Methods

randomR :: RandomGen g => (a, a) -> g -> (a, g) #

Takes a range (lo,hi) and a pseudo-random number generator g, and returns a pseudo-random value uniformly distributed over the closed interval [lo,hi], together with a new generator. It is unspecified what happens if lo>hi. For continuous types there is no requirement that the values lo and hi are ever produced, but they may be, depending on the implementation and the interval.

default randomR :: (RandomGen g, UniformRange a) => (a, a) -> g -> (a, g) #

random :: RandomGen g => g -> (a, g) #

The same as randomR, but using a default range determined by the type:

For bounded types (instances of Bounded, such as Char), the range is normally the whole type.
For fractional types, the range is normally the semi-closed interval [0,1).
For Integer, the range is (arbitrarily) the range of Int.

default random :: (RandomGen g, Uniform a) => g -> (a, g) #

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

Plural variant of randomR, producing an infinite list of pseudo-random values instead of returning a new generator.

randoms :: RandomGen g => g -> [a] #

Plural variant of random, producing an infinite list of pseudo-random values instead of returning a new generator.

Instances

Instances details

Random Bool #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Bool, Bool) -> g -> (Bool, g) # random :: RandomGen g => g -> (Bool, g) # randomRs :: RandomGen g => (Bool, Bool) -> g -> [Bool] # randoms :: RandomGen g => g -> [Bool] #
Random Char #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Char, Char) -> g -> (Char, g) # random :: RandomGen g => g -> (Char, g) # randomRs :: RandomGen g => (Char, Char) -> g -> [Char] # randoms :: RandomGen g => g -> [Char] #
Random Double #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Double, Double) -> g -> (Double, g) # random :: RandomGen g => g -> (Double, g) # randomRs :: RandomGen g => (Double, Double) -> g -> [Double] # randoms :: RandomGen g => g -> [Double] #
Random Float #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Float, Float) -> g -> (Float, g) # random :: RandomGen g => g -> (Float, g) # randomRs :: RandomGen g => (Float, Float) -> g -> [Float] # randoms :: RandomGen g => g -> [Float] #
Random Int #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Int, Int) -> g -> (Int, g) # random :: RandomGen g => g -> (Int, g) # randomRs :: RandomGen g => (Int, Int) -> g -> [Int] # randoms :: RandomGen g => g -> [Int] #
Random Int8 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Int8, Int8) -> g -> (Int8, g) # random :: RandomGen g => g -> (Int8, g) # randomRs :: RandomGen g => (Int8, Int8) -> g -> [Int8] # randoms :: RandomGen g => g -> [Int8] #
Random Int16 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Int16, Int16) -> g -> (Int16, g) # random :: RandomGen g => g -> (Int16, g) # randomRs :: RandomGen g => (Int16, Int16) -> g -> [Int16] # randoms :: RandomGen g => g -> [Int16] #
Random Int32 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Int32, Int32) -> g -> (Int32, g) # random :: RandomGen g => g -> (Int32, g) # randomRs :: RandomGen g => (Int32, Int32) -> g -> [Int32] # randoms :: RandomGen g => g -> [Int32] #
Random Int64 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Int64, Int64) -> g -> (Int64, g) # random :: RandomGen g => g -> (Int64, g) # randomRs :: RandomGen g => (Int64, Int64) -> g -> [Int64] # randoms :: RandomGen g => g -> [Int64] #
Random Integer #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Integer, Integer) -> g -> (Integer, g) # random :: RandomGen g => g -> (Integer, g) # randomRs :: RandomGen g => (Integer, Integer) -> g -> [Integer] # randoms :: RandomGen g => g -> [Integer] #
Random Word #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Word, Word) -> g -> (Word, g) # random :: RandomGen g => g -> (Word, g) # randomRs :: RandomGen g => (Word, Word) -> g -> [Word] # randoms :: RandomGen g => g -> [Word] #
Random Word8 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Word8, Word8) -> g -> (Word8, g) # random :: RandomGen g => g -> (Word8, g) # randomRs :: RandomGen g => (Word8, Word8) -> g -> [Word8] # randoms :: RandomGen g => g -> [Word8] #
Random Word16 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Word16, Word16) -> g -> (Word16, g) # random :: RandomGen g => g -> (Word16, g) # randomRs :: RandomGen g => (Word16, Word16) -> g -> [Word16] # randoms :: RandomGen g => g -> [Word16] #
Random Word32 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Word32, Word32) -> g -> (Word32, g) # random :: RandomGen g => g -> (Word32, g) # randomRs :: RandomGen g => (Word32, Word32) -> g -> [Word32] # randoms :: RandomGen g => g -> [Word32] #
Random Word64 #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (Word64, Word64) -> g -> (Word64, g) # random :: RandomGen g => g -> (Word64, g) # randomRs :: RandomGen g => (Word64, Word64) -> g -> [Word64] # randoms :: RandomGen g => g -> [Word64] #
Random CChar #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CChar, CChar) -> g -> (CChar, g) # random :: RandomGen g => g -> (CChar, g) # randomRs :: RandomGen g => (CChar, CChar) -> g -> [CChar] # randoms :: RandomGen g => g -> [CChar] #
Random CSChar #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CSChar, CSChar) -> g -> (CSChar, g) # random :: RandomGen g => g -> (CSChar, g) # randomRs :: RandomGen g => (CSChar, CSChar) -> g -> [CSChar] # randoms :: RandomGen g => g -> [CSChar] #
Random CUChar #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CUChar, CUChar) -> g -> (CUChar, g) # random :: RandomGen g => g -> (CUChar, g) # randomRs :: RandomGen g => (CUChar, CUChar) -> g -> [CUChar] # randoms :: RandomGen g => g -> [CUChar] #
Random CShort #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CShort, CShort) -> g -> (CShort, g) # random :: RandomGen g => g -> (CShort, g) # randomRs :: RandomGen g => (CShort, CShort) -> g -> [CShort] # randoms :: RandomGen g => g -> [CShort] #
Random CUShort #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CUShort, CUShort) -> g -> (CUShort, g) # random :: RandomGen g => g -> (CUShort, g) # randomRs :: RandomGen g => (CUShort, CUShort) -> g -> [CUShort] # randoms :: RandomGen g => g -> [CUShort] #
Random CInt #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CInt, CInt) -> g -> (CInt, g) # random :: RandomGen g => g -> (CInt, g) # randomRs :: RandomGen g => (CInt, CInt) -> g -> [CInt] # randoms :: RandomGen g => g -> [CInt] #
Random CUInt #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CUInt, CUInt) -> g -> (CUInt, g) # random :: RandomGen g => g -> (CUInt, g) # randomRs :: RandomGen g => (CUInt, CUInt) -> g -> [CUInt] # randoms :: RandomGen g => g -> [CUInt] #
Random CLong #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CLong, CLong) -> g -> (CLong, g) # random :: RandomGen g => g -> (CLong, g) # randomRs :: RandomGen g => (CLong, CLong) -> g -> [CLong] # randoms :: RandomGen g => g -> [CLong] #
Random CULong #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CULong, CULong) -> g -> (CULong, g) # random :: RandomGen g => g -> (CULong, g) # randomRs :: RandomGen g => (CULong, CULong) -> g -> [CULong] # randoms :: RandomGen g => g -> [CULong] #
Random CLLong #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CLLong, CLLong) -> g -> (CLLong, g) # random :: RandomGen g => g -> (CLLong, g) # randomRs :: RandomGen g => (CLLong, CLLong) -> g -> [CLLong] # randoms :: RandomGen g => g -> [CLLong] #
Random CULLong #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CULLong, CULLong) -> g -> (CULLong, g) # random :: RandomGen g => g -> (CULLong, g) # randomRs :: RandomGen g => (CULLong, CULLong) -> g -> [CULLong] # randoms :: RandomGen g => g -> [CULLong] #
Random CFloat #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CFloat, CFloat) -> g -> (CFloat, g) # random :: RandomGen g => g -> (CFloat, g) # randomRs :: RandomGen g => (CFloat, CFloat) -> g -> [CFloat] # randoms :: RandomGen g => g -> [CFloat] #
Random CDouble #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CDouble, CDouble) -> g -> (CDouble, g) # random :: RandomGen g => g -> (CDouble, g) # randomRs :: RandomGen g => (CDouble, CDouble) -> g -> [CDouble] # randoms :: RandomGen g => g -> [CDouble] #
Random CPtrdiff #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CPtrdiff, CPtrdiff) -> g -> (CPtrdiff, g) # random :: RandomGen g => g -> (CPtrdiff, g) # randomRs :: RandomGen g => (CPtrdiff, CPtrdiff) -> g -> [CPtrdiff] # randoms :: RandomGen g => g -> [CPtrdiff] #
Random CSize #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CSize, CSize) -> g -> (CSize, g) # random :: RandomGen g => g -> (CSize, g) # randomRs :: RandomGen g => (CSize, CSize) -> g -> [CSize] # randoms :: RandomGen g => g -> [CSize] #
Random CWchar #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CWchar, CWchar) -> g -> (CWchar, g) # random :: RandomGen g => g -> (CWchar, g) # randomRs :: RandomGen g => (CWchar, CWchar) -> g -> [CWchar] # randoms :: RandomGen g => g -> [CWchar] #
Random CSigAtomic #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CSigAtomic, CSigAtomic) -> g -> (CSigAtomic, g) # random :: RandomGen g => g -> (CSigAtomic, g) # randomRs :: RandomGen g => (CSigAtomic, CSigAtomic) -> g -> [CSigAtomic] # randoms :: RandomGen g => g -> [CSigAtomic] #
Random CIntPtr #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CIntPtr, CIntPtr) -> g -> (CIntPtr, g) # random :: RandomGen g => g -> (CIntPtr, g) # randomRs :: RandomGen g => (CIntPtr, CIntPtr) -> g -> [CIntPtr] # randoms :: RandomGen g => g -> [CIntPtr] #
Random CUIntPtr #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CUIntPtr, CUIntPtr) -> g -> (CUIntPtr, g) # random :: RandomGen g => g -> (CUIntPtr, g) # randomRs :: RandomGen g => (CUIntPtr, CUIntPtr) -> g -> [CUIntPtr] # randoms :: RandomGen g => g -> [CUIntPtr] #
Random CIntMax #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CIntMax, CIntMax) -> g -> (CIntMax, g) # random :: RandomGen g => g -> (CIntMax, g) # randomRs :: RandomGen g => (CIntMax, CIntMax) -> g -> [CIntMax] # randoms :: RandomGen g => g -> [CIntMax] #
Random CUIntMax #
Instance details Defined in System.Random Methods randomR :: RandomGen g => (CUIntMax, CUIntMax) -> g -> (CUIntMax, g) # random :: RandomGen g => g -> (CUIntMax, g) # randomRs :: RandomGen g => (CUIntMax, CUIntMax) -> g -> [CUIntMax] # randoms :: RandomGen g => g -> [CUIntMax] #

class Uniform a #

The class of types for which a uniformly distributed value can be drawn from all possible values of the type.

Since: 1.2.0

Minimal complete definition

uniformM

Instances

Instances details

Uniform Bool #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Bool #
Uniform Char #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Char #
Uniform Int #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Int #
Uniform Int8 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Int8 #
Uniform Int16 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Int16 #
Uniform Int32 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Int32 #
Uniform Int64 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Int64 #
Uniform Word #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Word #
Uniform Word8 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Word8 #
Uniform Word16 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Word16 #
Uniform Word32 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Word32 #
Uniform Word64 #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m Word64 #
Uniform CChar #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CChar #
Uniform CSChar #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CSChar #
Uniform CUChar #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CUChar #
Uniform CShort #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CShort #
Uniform CUShort #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CUShort #
Uniform CInt #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CInt #
Uniform CUInt #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CUInt #
Uniform CLong #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CLong #
Uniform CULong #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CULong #
Uniform CLLong #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CLLong #
Uniform CULLong #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CULLong #
Uniform CBool #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CBool #
Uniform CPtrdiff #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CPtrdiff #
Uniform CSize #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CSize #
Uniform CWchar #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CWchar #
Uniform CSigAtomic #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CSigAtomic #
Uniform CIntPtr #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CIntPtr #
Uniform CUIntPtr #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CUIntPtr #
Uniform CIntMax #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CIntMax #
Uniform CUIntMax #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m CUIntMax #
(Uniform a, Uniform b) => Uniform (a, b) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m (a, b) #
(Uniform a, Uniform b, Uniform c) => Uniform (a, b, c) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m (a, b, c) #
(Uniform a, Uniform b, Uniform c, Uniform d) => Uniform (a, b, c, d) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m (a, b, c, d) #
(Uniform a, Uniform b, Uniform c, Uniform d, Uniform e) => Uniform (a, b, c, d, e) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m (a, b, c, d, e) #
(Uniform a, Uniform b, Uniform c, Uniform d, Uniform e, Uniform f) => Uniform (a, b, c, d, e, f) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g m => g -> m (a, b, c, d, e, f) #
(Uniform a, Uniform b, Uniform c, Uniform d, Uniform e, Uniform f, Uniform g) => Uniform (a, b, c, d, e, f, g) #
Instance details Defined in System.Random.Internal Methods uniformM :: StatefulGen g0 m => g0 -> m (a, b, c, d, e, f, g) #

class UniformRange a #

The class of types for which a uniformly distributed value can be drawn from a range.

Since: 1.2.0

Minimal complete definition

uniformRM

Instances

Instances details

UniformRange Bool #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Bool, Bool) -> g -> m Bool #
UniformRange Char #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Char, Char) -> g -> m Char #
UniformRange Double #	See Floating point number caveats.
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Double, Double) -> g -> m Double #
UniformRange Float #	See Floating point number caveats.
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Float, Float) -> g -> m Float #
UniformRange Int #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Int, Int) -> g -> m Int #
UniformRange Int8 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Int8, Int8) -> g -> m Int8 #
UniformRange Int16 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Int16, Int16) -> g -> m Int16 #
UniformRange Int32 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Int32, Int32) -> g -> m Int32 #
UniformRange Int64 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Int64, Int64) -> g -> m Int64 #
UniformRange Integer #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Integer, Integer) -> g -> m Integer #
UniformRange Natural #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Natural, Natural) -> g -> m Natural #
UniformRange Word #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Word, Word) -> g -> m Word #
UniformRange Word8 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Word8, Word8) -> g -> m Word8 #
UniformRange Word16 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Word16, Word16) -> g -> m Word16 #
UniformRange Word32 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Word32, Word32) -> g -> m Word32 #
UniformRange Word64 #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (Word64, Word64) -> g -> m Word64 #
UniformRange CChar #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CChar, CChar) -> g -> m CChar #
UniformRange CSChar #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CSChar, CSChar) -> g -> m CSChar #
UniformRange CUChar #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CUChar, CUChar) -> g -> m CUChar #
UniformRange CShort #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CShort, CShort) -> g -> m CShort #
UniformRange CUShort #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CUShort, CUShort) -> g -> m CUShort #
UniformRange CInt #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CInt, CInt) -> g -> m CInt #
UniformRange CUInt #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CUInt, CUInt) -> g -> m CUInt #
UniformRange CLong #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CLong, CLong) -> g -> m CLong #
UniformRange CULong #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CULong, CULong) -> g -> m CULong #
UniformRange CLLong #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CLLong, CLLong) -> g -> m CLLong #
UniformRange CULLong #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CULLong, CULLong) -> g -> m CULLong #
UniformRange CBool #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CBool, CBool) -> g -> m CBool #
UniformRange CFloat #	See Floating point number caveats.
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CFloat, CFloat) -> g -> m CFloat #
UniformRange CDouble #	See Floating point number caveats.
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CDouble, CDouble) -> g -> m CDouble #
UniformRange CPtrdiff #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CPtrdiff, CPtrdiff) -> g -> m CPtrdiff #
UniformRange CSize #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CSize, CSize) -> g -> m CSize #
UniformRange CWchar #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CWchar, CWchar) -> g -> m CWchar #
UniformRange CSigAtomic #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CSigAtomic, CSigAtomic) -> g -> m CSigAtomic #
UniformRange CIntPtr #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CIntPtr, CIntPtr) -> g -> m CIntPtr #
UniformRange CUIntPtr #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CUIntPtr, CUIntPtr) -> g -> m CUIntPtr #
UniformRange CIntMax #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CIntMax, CIntMax) -> g -> m CIntMax #
UniformRange CUIntMax #
Instance details Defined in System.Random.Internal Methods uniformRM :: StatefulGen g m => (CUIntMax, CUIntMax) -> g -> m CUIntMax #

Standard pseudo-random number generator

data StdGen #

The standard pseudo-random number generator.

Instances

Instances details

Eq StdGen #
Instance details Defined in System.Random.Internal Methods (==) :: StdGen -> StdGen -> Bool # (/=) :: StdGen -> StdGen -> Bool #
Show StdGen #
Instance details Defined in System.Random.Internal Methods showsPrec :: Int -> StdGen -> ShowS # show :: StdGen -> String # showList :: [StdGen] -> ShowS #
NFData StdGen #
Instance details Defined in System.Random.Internal Methods rnf :: StdGen -> () #
RandomGen StdGen #
Instance details Defined in System.Random.Internal Methods next :: StdGen -> (Int, StdGen) # genWord8 :: StdGen -> (Word8, StdGen) # genWord16 :: StdGen -> (Word16, StdGen) # genWord32 :: StdGen -> (Word32, StdGen) # genWord64 :: StdGen -> (Word64, StdGen) # genWord32R :: Word32 -> StdGen -> (Word32, StdGen) # genWord64R :: Word64 -> StdGen -> (Word64, StdGen) # genShortByteString :: Int -> StdGen -> (ShortByteString, StdGen) # genRange :: StdGen -> (Int, Int) # split :: StdGen -> (StdGen, StdGen) #

mkStdGen :: Int -> StdGen #

Constructs a StdGen deterministically.

Global standard pseudo-random number generator

There is a single, implicit, global pseudo-random number generator of type StdGen, held in a global variable maintained by the IO monad. It is initialised automatically in some system-dependent fashion. To get deterministic behaviour, use setStdGen.

Note that mkStdGen also gives deterministic behaviour without requiring an IO context.

getStdRandom :: MonadIO m => (StdGen -> (a, StdGen)) -> m a #

Uses the supplied function to get a value from the current global random generator, and updates the global generator with the new generator returned by the function. For example, rollDice gets a pseudo-random integer between 1 and 6:

 rollDice :: IO Int
 rollDice = getStdRandom (randomR (1,6))

getStdGen :: MonadIO m => m StdGen #

Gets the global pseudo-random number generator.

setStdGen :: MonadIO m => StdGen -> m () #

Sets the global pseudo-random number generator.

newStdGen :: MonadIO m => m StdGen #

Applies split to the current global pseudo-random generator, updates it with one of the results, and returns the other.

randomIO :: (Random a, MonadIO m) => m a #

A variant of random that uses the global pseudo-random number generator.

randomRIO :: (Random a, MonadIO m) => (a, a) -> m a #

A variant of randomR that uses the global pseudo-random number generator.

Compatibility and reproducibility

Backwards compatibility and deprecations

Version 1.2 mostly maintains backwards compatibility with version 1.1. This has a few consequences users should be aware of:

The type class Random is only provided for backwards compatibility. New code should use Uniform and UniformRange instead.
The methods next and genRange in RandomGen are deprecated and only provided for backwards compatibility. New instances of RandomGen should implement word-based methods instead. See below for more information about how to write a RandomGen instance.
This library provides instances for Random for some unbounded types for backwards compatibility. For an unbounded type, there is no way to generate a value with uniform probability out of its entire domain, so the random implementation for unbounded types actually generates a value based on some fixed range.
For Integer, random generates a value in the Int range. For Float and Double, random generates a floating point value in the range [0, 1).
This library does not provide Uniform instances for any unbounded types.

Reproducibility

If you have two builds of a particular piece of code against this library, any deterministic function call should give the same result in the two builds if the builds are

compiled against the same major version of this library
on the same architecture (32-bit or 64-bit)

Notes for pseudo-random number generator implementors

How to implement `RandomGen`

Consider these points when writing a RandomGen instance for a given pure pseudo-random number generator:

If the pseudo-random number generator has a power-of-2 modulus, that is, it natively outputs 2^n bits of randomness for some n, implement genWord8, genWord16, genWord32 and genWord64. See below for more details.
If the pseudo-random number generator does not have a power-of-2 modulus, implement next and genRange. See below for more details.
If the pseudo-random number generator is splittable, implement split. If there is no suitable implementation, split should fail with a helpful error message.

How to implement `RandomGen` for a pseudo-random number generator with power-of-2 modulus

Suppose you want to implement a permuted congruential generator.

>>> data PCGen = PCGen !Word64 !Word64

It produces a full Word32 of randomness per iteration.

>>> import Data.Bits
>>> :{
let stepGen :: PCGen -> (Word32, PCGen)
    stepGen (PCGen state inc) = let
      newState = state * 6364136223846793005 + (inc .|. 1)
      xorShifted = fromIntegral (((state `shiftR` 18) `xor` state) `shiftR` 27) :: Word32
      rot = fromIntegral (state `shiftR` 59) :: Word32
      out = (xorShifted `shiftR` (fromIntegral rot)) .|. (xorShifted `shiftL` fromIntegral ((-rot) .&. 31))
      in (out, PCGen newState inc)
:}

>>> fst $ stepGen $ snd $ stepGen (PCGen 17 29)
3288430965

You can make it an instance of RandomGen as follows:

>>> :{
instance RandomGen PCGen where
  genWord32 = stepGen
  split _ = error "PCG is not splittable"
:}

How to implement `RandomGen` for a pseudo-random number generator without a power-of-2 modulus

We do not recommend you implement any new pseudo-random number generators without a power-of-2 modulus.

Pseudo-random number generators without a power-of-2 modulus perform significantly worse than pseudo-random number generators with a power-of-2 modulus with this library. This is because most functionality in this library is based on generating and transforming uniformly pseudo-random machine words, and generating uniformly pseudo-random machine words using a pseudo-random number generator without a power-of-2 modulus is expensive.

The pseudo-random number generator from L’Ecuyer (1988) natively generates an integer value in the range [1, 2147483562]. This is the generator used by this library before it was replaced by SplitMix in version 1.2.

>>> data LegacyGen = LegacyGen !Int32 !Int32
>>> :{
let legacyNext :: LegacyGen -> (Int, LegacyGen)
    legacyNext (LegacyGen s1 s2) = (fromIntegral z', LegacyGen s1'' s2'') where
      z' = if z < 1 then z + 2147483562 else z
      z = s1'' - s2''
      k = s1 `quot` 53668
      s1'  = 40014 * (s1 - k * 53668) - k * 12211
      s1'' = if s1' < 0 then s1' + 2147483563 else s1'
      k' = s2 `quot` 52774
      s2' = 40692 * (s2 - k' * 52774) - k' * 3791
      s2'' = if s2' < 0 then s2' + 2147483399 else s2'
:}

You can make it an instance of RandomGen as follows:

>>> :{
instance RandomGen LegacyGen where
  next = legacyNext
  genRange _ = (1, 2147483562)
  split _ = error "Not implemented"
:}

References

Guy L. Steele, Jr., Doug Lea, and Christine H. Flood. 2014. Fast splittable pseudorandom number generators. In Proceedings of the 2014 ACM International Conference on Object Oriented Programming Systems Languages & Applications (OOPSLA '14). ACM, New York, NY, USA, 453-472. DOI: https://doi.org/10.1145/2660193.2660195

Introduction

Usage

Pure number generator interface

Instances

Examples

Examples

Examples

Instances

Instances

Instances

Standard pseudo-random number generator

Instances

Global standard pseudo-random number generator

Compatibility and reproducibility

Backwards compatibility and deprecations

Reproducibility

Notes for pseudo-random number generator implementors

How to implement RandomGen

How to implement RandomGen for a pseudo-random number generator with power-of-2 modulus

How to implement RandomGen for a pseudo-random number generator without a power-of-2 modulus

References

How to implement `RandomGen`

How to implement `RandomGen` for a pseudo-random number generator with power-of-2 modulus

How to implement `RandomGen` for a pseudo-random number generator without a power-of-2 modulus