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This library provides pseudo-random number generators (PRNGs) comparable to that of the Random module from OCaml's standard library, but with two extensions:
split
operation that returns a new generator that is statistically independent from the current generator. Both generators can be used in parallel, and can be further splitted, without introducing statistical bias. This splitting operation is particularly useful to implement the lazy generation of pseudo-random infinite data structures such as functions or streams.Random.State
standard library module, another, purely functional interface is provided. In the functional interface, the current state of the PRNG appears as parameter but also as result of the number generation functions. This interface can be used directly within a state monad.module type STATE = sig ... end
In this alternate interface, number-generating functions do not update the current state of the generator in-place. Instead, they return the updated generator as a second result. It is the programmer's responsibility to correctly thread the generators through the program, typically by using a state monad.
All operations of the STATE
interface are provided except bytes
(too imperative) and copy
, reseed
and remake
(pointless).
module type PURE = sig ... end
module Splitmix : sig ... end
This is an implementation of the STATE
and PURE
interfaces based on the Splitmix design by Guy L. Steele Jr., Doug Lea, and Christine H. Flood.
module Chacha : sig ... end
This is an implementation of the STATE
and PURE
interfaces based on the Chacha 20 stream cipher by D. J. Bernstein.
For seeding, 128 bits of entropy is recommended. Seeds of up to 32 characters are used as keys to the Chacha 20 cipher. Characters beyond the first 32 are ignored.
Reseeding is recommended after 264 numbers have been generated.