| Safe Haskell | None |
|---|---|
| Language | Haskell98 |
Data.Random.Source.PureMT
Contents
Description
This module provides functions useful for implementing new MonadRandom
and RandomSource instances for state-abstractions containing PureMT
values (the pure pseudorandom generator provided by the
mersenne-random-pure64 package), as well as instances for some common
cases.
A PureMT generator is immutable, so PureMT by itself cannot be a
RandomSource (if it were, it would always give the same "random"
values). Some form of mutable state must be used, such as an IORef,
State monad, etc.. A few default instances are provided by this module
along with a more-general function (getRandomPrimFromMTRef) usable as
an implementation for new cases users might need.
Documentation
PureMT, a pure mersenne twister pseudo-random number generator
Instances
Create a new PureMT generator, using the clocktime as the base for the seed.
getRandomPrimFromMTRef :: ModifyRef sr m PureMT => sr -> Prim a -> m a Source #
Given a mutable reference to a PureMT generator, we can implement
RandomSource for it in any monad in which the reference can be modified.
Typically this would be used to define a new RandomSource instance for
some new reference type or new monad in which an existing reference type
can be modified atomically. As an example, the following instance could
be used to describe how IORef PureMT can be a RandomSource in the
IO monad:
instance RandomSource IO (IORef PureMT) where
supportedPrimsFrom _ _ = True
getSupportedRandomPrimFrom = getRandomPrimFromMTRef(note that there is actually a more general instance declared already covering this as a a special case, so there's no need to repeat this declaration anywhere)
Example usage (using some functions from Data.Random in the random-fu package):
main = do
src <- newIORef (pureMT 1234) -- OR: newPureMT >>= newIORef
x <- runRVar (uniform 0 100) src :: IO Double
print x