random-source-0.3: Generic basis for random number generators



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.



data PureMT

PureMT, a pure mersenne twister pseudo-random number generator

newPureMT :: IO PureMT

Create a new PureMT generator, using the clocktime as the base for the seed.

pureMT :: Word64 -> PureMT

Create a PureMT generator from a Word64 seed.

getRandomPrimFromMTRef :: ModifyRef sr m PureMT => sr -> Prim a -> m aSource

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