Data.Random.Source.StdGen

This module provides functions useful for implementing new MonadRandom and RandomSource instances for state-abstractions containing StdGen values (the pure pseudorandom generator provided by the System.Random module in the "random" package), as well as instances for some common cases.

Documentation

data StdGen

The StdGen instance of RandomGen has a genRange of at least 30 bits.

The result of repeatedly using next should be at least as statistically robust as the Minimal Standard Random Number Generator described by [System.Random, System.Random]. Until more is known about implementations of split, all we require is that split deliver generators that are (a) not identical and (b) independently robust in the sense just given.

The Show and Read instances of StdGen provide a primitive way to save the state of a random number generator. It is required that read (show g) == g.

In addition, reads may be used to map an arbitrary string (not necessarily one produced by show) onto a value of type StdGen. In general, the Read instance of StdGen has the following properties:

• It guarantees to succeed on any string.
• It guarantees to consume only a finite portion of the string.
• Different argument strings are likely to result in different results.

Instances

Read StdGen

Show StdGen

RandomGen StdGen

(Monad m, ModifyRef (IORef StdGen) m StdGen) => RandomSource m (IORef StdGen)

(Monad m, ModifyRef (STRef s StdGen) m StdGen) => RandomSource m (STRef s StdGen)

(Monad m1, ModifyRef (Ref m2 StdGen) m1 StdGen) => RandomSource m1 (Ref m2 StdGen)

Monad m => MonadRandom (StateT StdGen m)

Monad m => MonadRandom (StateT StdGen m)

mkStdGen :: Int -> StdGen

The function mkStdGen provides an alternative way of producing an initial generator, by mapping an Int into a generator. Again, distinct arguments should be likely to produce distinct generators.

newStdGen :: IO StdGen

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

getRandomPrimFromStdGenIO :: Prim a -> IO a

getRandomPrimFromRandomGenRef :: (Monad m, ModifyRef sr m g, RandomGen g) => sr -> Prim a -> m a

Given a mutable reference to a RandomGen generator, we can make a RandomSource usable in any monad in which the reference can be modified.

See Data.Random.Source.PureMT.getRandomPrimFromMTRef for more detailed usage hints - this function serves exactly the same purpose except for a StdGen generator instead of a PureMT generator.

getRandomPrimFromRandomGenState :: forall g m a. (RandomGen g, MonadState g m) => Prim a -> m a

Similarly, getRandomWordFromRandomGenState x can be used in any "state" monad in the mtl sense whose state is a RandomGen generator. Additionally, the standard mtl state monads have MonadRandom instances which do precisely that, allowing an easy conversion of RVars and other Distribution instances to "pure" random variables.

Again, see Data.Random.Source.PureMT.getRandomPrimFromMTState for more detailed usage hints - this function serves exactly the same purpose except for a StdGen generator instead of a PureMT generator.