Question

What are the recommended Haskell packages for pure pseudo-random generators (uniform Doubles)?

I’m interested in a convenient API in the first place, speed would be nice too.

Maybe mwc-random?

Answer 1

The standard System.Random has a pure interface. I would recommend wrapping it in a State g (for whatever generator g you’re using) to avoid threading the state; the state function makes turning functions like next into stateful actions easy:

next :: (RandomGen g) => g -> (Int, g)
state :: (s -> (a, s)) -> State s a
state next :: (RandomGen g) => State g Int

The MonadRandom package is based on the State g interface with pre-written wrappers for the generator functions; I think it’s fairly popular.

Note that you can still run actions using this pure interface on the global RNG. MonadRandom has evalRandIO for the purpose.

I think you could write an (orphan) RandomGen instance to use mwc-random with these.