| Safe Haskell | None |
|---|
Data.Random.Source.StdGen
Description
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.
- data StdGen
- mkStdGen :: Int -> StdGen
- newStdGen :: IO StdGen
- getRandomPrimFromStdGenIO :: Prim a -> IO a
- getRandomPrimFromRandomGenRef :: (Monad m, ModifyRef sr m g, RandomGen g) => sr -> Prim a -> m a
- getRandomPrimFromRandomGenState :: forall g m a. (RandomGen g, MonadState g m) => Prim a -> m a
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) |
Applies split to the current global random generator,
updates it with one of the results, and returns the other.
getRandomPrimFromStdGenIO :: Prim a -> IO aSource
getRandomPrimFromRandomGenRef :: (Monad m, ModifyRef sr m g, RandomGen g) => sr -> Prim a -> m aSource
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 aSource
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.