Copyright | (c) Antony Courtney and Henrik Nilsson, Yale University, 2003 |
---|---|

License | BSD-style (see the LICENSE file in the distribution) |

Maintainer | ivan.perez@keera.co.uk |

Stability | provisional |

Portability | non-portable (GHC extensions) |

Safe Haskell | None |

Language | Haskell98 |

# Documentation

class RandomGen g where

The class `RandomGen`

provides a common interface to random number
generators.

The `next`

operation returns an `Int`

that is uniformly distributed
in the range returned by `genRange`

(including both end points),
and a new generator.

The `genRange`

operation yields the range of values returned by
the generator.

It is required that:

The second condition ensures that `genRange`

cannot examine its
argument, and hence the value it returns can be determined only by the
instance of `RandomGen`

. That in turn allows an implementation to make
a single call to `genRange`

to establish a generator's range, without
being concerned that the generator returned by (say) `next`

might have
a different range to the generator passed to `next`

.

The default definition spans the full range of `Int`

.

split :: g -> (g, g)

The `split`

operation allows one to obtain two distinct random number
generators. This is very useful in functional programs (for example, when
passing a random number generator down to recursive calls), but very
little work has been done on statistically robust implementations of
`split`

([System.Random, System.Random]
are the only examples we know of).

class Random a where

With a source of random number supply in hand, the `Random`

class allows the
programmer to extract random values of a variety of types.

randomR :: RandomGen g => (a, a) -> g -> (a, g)

Takes a range *(lo,hi)* and a random number generator
*g*, and returns a random value uniformly distributed in the closed
interval *[lo,hi]*, together with a new generator. It is unspecified
what happens if *lo>hi*. For continuous types there is no requirement
that the values *lo* and *hi* are ever produced, but they may be,
depending on the implementation and the interval.

random :: RandomGen g => g -> (a, g)

The same as `randomR`

, but using a default range determined by the type:

randomRs :: RandomGen g => (a, a) -> g -> [a]

Plural variant of `randomR`

, producing an infinite list of
random values instead of returning a new generator.

randoms :: RandomGen g => g -> [a]

Plural variant of `random`

, producing an infinite list of
random values instead of returning a new generator.

A variant of `randomR`

that uses the global random number generator
(see System.Random).

A variant of `random`

that uses the global random number generator
(see System.Random).

# Noise (random signal) sources and stochastic event sources

noise :: (RandomGen g, Random b) => g -> SF a b Source

Noise (random signal) with default range for type in question; based on "randoms".

noiseR :: (RandomGen g, Random b) => (b, b) -> g -> SF a b Source

Noise (random signal) with specified range; based on "randomRs".

occasionally :: RandomGen g => g -> Time -> b -> SF a (Event b) Source

Stochastic event source with events occurring on average once every t_avg seconds. However, no more than one event results from any one sampling interval in the case of relatively sparse sampling, thus avoiding an "event backlog" should sampling become more frequent at some later point in time.