System.Random.Internal

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

StdGen is the standard RandomGen instance provided by this library.

Pseudo-random generators that can be split into two separate and independent psuedo-random generators should provide an instance for this type class.

Historically this functionality was included in the RandomGen type class in the split function, however, few pseudo-random generators possess this property of splittability. This lead the old split function being usually implemented in terms of error.

This is a binary form of pseudo-random number generator's state. It is designed to be safe and easy to use for input/output operations like restoring from file, transmitting over the network, etc.

Constructor is not exported, becasue it is important for implementation to enforce the invariant of the underlying byte array being of the exact same length as the generator has specified in SeedSize. Use mkSeed and unSeed to get access to the raw bytes in a safe manner.

StatefulGen is an interface to monadic pseudo-random number generators.

This class is designed for mutable pseudo-random number generators that have a frozen imutable counterpart that can be manipulated in pure code.

It also works great with frozen generators that are based on pure generators that have a RandomGen instance.

Here are a few laws, which are important for this type class:

• Roundtrip and complete destruction on overwrite:

overwriteGen mg fg >> freezeGen mg = pure fg

• Modification of a mutable generator:

overwriteGen mg fg = modifyGen mg (const ((), fg)

• Freezing of a mutable generator:

freezeGen mg = modifyGen mg (fg -> (fg, fg))

Functionality for thawing frozen generators is not part of the FrozenGen class, becase not all mutable generators support functionality of creating new mutable generators, which is what thawing is in its essence. For this reason StateGen does not have an instance for this type class, but it has one for FrozenGen.

Here is an important law that relates this type class to FrozenGen

• Roundtrip and independence of mutable generators:

traverse thawGen fgs >>= traverse freezeGen = pure fgs

Splits a pseudo-random number generator into two. Overwrites the mutable pseudo-random number generator with one of the immutable pseudo-random number generators produced by a split function and returns the other.

Splits a pseudo-random number generator into two. Overwrites the mutable wrapper with one of the resulting generators and returns the other as a new mutable generator.

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

A definition of Uniform for Finite types. If your data has several fields of sub-Word cardinality, this instance may be more efficient than one, derived via Generic and GUniform.

>>> :seti -XDeriveGeneric -XDeriveAnyClass>>> import GHC.Generics (Generic)>>> import System.Random.Stateful>>> data Triple = Triple Word8 Word8 Word8 deriving (Show, Generic, Finite)>>> instance Uniform Triple where uniformM = uniformViaFiniteM>>> gen <- newIOGenM (mkStdGen 42)>>> uniformListM 5 gen :: IO [Triple][Triple 60 226 48,Triple 234 194 151,Triple 112 96 95,Triple 51 251 15,Triple 6 0 208]

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

Architecture specific Word generation in the specified lower range

Generates uniformly distributed Double in the range [0, 1]. Numbers are generated by generating uniform Word64 and dividing it by 2^{64}. It's used to implement UniformRange instance for Double.

Generates uniformly distributed Double in the range (0, 1]. Number is generated as 2^{-64}/2+\operatorname{uniformDouble01M}. Constant is 1/2 of smallest nonzero value which could be generated by uniformDouble01M.

Generates uniformly distributed Float in the range [0, 1]. Numbers are generated by generating uniform Word32 and dividing it by 2^{32}. It's used to implement UniformRange instance for Float.

Generates uniformly distributed Float in the range (0, 1]. Number is generated as 2^{-32}/2+\operatorname{uniformFloat01M}. Constant is 1/2 of smallest nonzero value which could be generated by uniformFloat01M.

Generates uniformly distributed Enum. One can use it to define a Uniform instance:

data Colors = Red | Green | Blue deriving (Enum, Bounded)
instance Uniform Colors where uniformM = uniformEnumM

Generates uniformly distributed Enum in the given range. One can use it to define a UniformRange instance:

data Colors = Red | Green | Blue deriving (Enum)
instance UniformRange Colors where
  uniformRM = uniformEnumRM
  inInRange (lo, hi) x = isInRange (fromEnum lo, fromEnum hi) (fromEnum x)

Generates a list of pseudo-random values.

Examples

>>> import System.Random.Stateful>>> let pureGen = mkStdGen 137>>> g <- newIOGenM pureGen>>> uniformListM 10 g :: IO [Bool][True,True,True,True,False,True,True,False,False,False]

Generates a list of pseudo-random values in a specified range.

Examples

>>> import System.Random.Stateful>>> let pureGen = mkStdGen 137>>> g <- newIOGenM pureGen>>> uniformListRM 10 (20, 30) g :: IO [Int][23,21,28,25,28,28,26,25,29,27]

Utilize Ord instance to decide if a value is within the range. Designed to be used for implementing isInRange

Utilize Enum instance to decide if a value is within the range. Designed to be used for implementing isInRange

This is the function that is used to scale a floating point value from random word range to the custom [low, high] range.

uniformShortByteString n g generates a ShortByteString of length n filled with pseudo-random bytes.

Efficiently generates a sequence of pseudo-random bytes in a platform independent manner.

Using an ST action that generates 8 bytes at a time fill in a new ByteArray in architecture agnostic manner.

Efficiently fills in a new ShortByteString in a platform independent manner.

Same as genShortByteStringIO, but runs in ST.

Efficiently generates a sequence of pseudo-random bytes in a platform independent manner.