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A Prompt GADT describing a request for a primitive random variate. Random variable definitions will request their entropy via these prompts, and entropy sources will satisfy those requests. The functions in Data.Random.Source.Internal.TH extend incomplete entropy-source definitions to complete ones, essentially defining a very flexible implementation-defaulting system.

Some possible future additions: PrimFloat :: Prim Float PrimInt :: Prim Int PrimPair :: Prim a -> Prim b -> Prim (a :*: b) PrimNormal :: Prim Double PrimChoice :: [(Double :*: a)] -> Prim a PrimBytes :: !Int -> Prim ByteString

Unfortunately, I cannot get Haddock to accept my comments about the data constructors, but hopefully they should be reasonably self-explanatory.

A typeclass for monads with a chosen source of entropy. For example, RVar is such a monad - the source from which it is (eventually) sampled is the only source from which a random variable is permitted to draw, so when directly requesting entropy for a random variable these functions are used.

Minimum implementation is either the internal getRandomPrim or all other functions. Additionally, this class's interface is subject to extension at any time, so it is very, very strongly recommended that the monadRandom Template Haskell function be used to implement this function rather than directly implementing it. That function takes care of choosing default implementations for any missing functions; as long as at least one function is implemented, it will derive sensible implementations of all others.

To use monadRandom, just wrap your instance declaration as follows (and enable the TemplateHaskell and GADTs language extensions):

$(monadRandom [d|
        instance MonadRandom FooM where
            getRandomDouble = return pi
            getRandomWord16 = return 4
            {- etc... -}
    |])

A source of entropy which can be used in the given monad.

See also MonadRandom.

Minimum implementation is either the internal getRandomPrimFrom or all other functions. Additionally, this class's interface is subject to extension at any time, so it is very, very strongly recommended that the randomSource Template Haskell function be used to implement this function rather than directly implementing it. That function takes care of choosing default implementations for any missing functions; as long as at least one function is implemented, it will derive sensible implementations of all others.

To use randomSource, just wrap your instance declaration as follows (and enable the TemplateHaskell, MultiParamTypeClasses and GADTs language extensions, as well as any others required by your instances, such as FlexibleInstances):

$(randomSource [d|
        instance RandomSource FooM Bar where
            {- at least one RandomSource function... -}
    |])

This type provides a way to define a RandomSource for a monad without actually having to declare an instance.