syaiful6/purescript-stdgen

Pure random generator for purescript

Purescript Std-Random

This is port of Haskell's System Random, but with different API and has been recast in a form suitable for Purescript ecosystem. This lib depend and implements MonadGen defined on purescript-gen.

Getting Started

The most basic use case is to choose an item in a collection:

chooseCard :: NonEmpty f (StdGen a) -> StdGen a
chooseCard xs = oneOf xs

To run StdGen you need StdSeed, you can manually create it using mkStdSeed or by using randomStdSeed that use Javascript's random. Usually you want to hold StdSeed after it created on mutable variable, and update it after you use it.

main = do
  seed <- randomStdSeed
  seedref <- newRef seed
  let Tuple seed1 seed2 = splitStdSeed seed
  log $ evalStdGen (chooseCard cards) (GenState seed1 10)
  -- modify the seed to use next time
  writeRef seedref seed2
  -- rest program

Ceveats

• The lib only provides pseudo-random generator, it is not a source for cryptographic quality random bits.
• The random generator defined here is pure, meaning it will generate the same sequence each time they are called with the same Seed.