Copyright | (c) 2012-2013 Michał Pałka |
---|---|

License | BSD3 |

Maintainer | michal.palka@chalmers.se |

Stability | experimental |

Portability | portable |

Safe Haskell | None |

Language | Haskell98 |

# Documentation

The generator type

class RandomGen g where Source #

Alternative `RandomGen`

class with a modified `next`

operation, and added `splitn`

and `level`

operations.

Using the generator requires that no more than one operation is called
on the same generator state, as the implementation does not guarantee pseudorandomness
otherwise. As an exception, calling `splitn`

many times on the same generator state is
allowed as long as the 'bits' argument is the same for all the calls.

next :: g -> (Word32, g) Source #

`next`

returns a `Word32`

that appears to have been chosen uniformly at random, and a
new generator state.

`split`

returns two derived generator states that appear to be independent pseudorandom
number generators.

:: g | Original generator state. |

-> Int | Number of bits that will be used to index the derived states. Must be between 0 and 32. |

-> Word32 | Index of the derived state. Call to |

-> g |

`splitn`

is the n-way split operation used to create many derived generator states
in one go. Application of `splitn`

to two first arguments should be shared between
different applications of the index argument to avoid unnecessary repeated computations.

The following code creates ten 'independent' generator states. Number '4' comes from the fact that at least four bits are needed to encode ten different indices.

f :: RandomGen g => g -> [g] f r = map (splitn r 4) [0..9]

`level`

is a 'hint' operation that may cause an iteration of work
of the generator be performed prematurely in order to
prevent the subsequent operations from being expensive. It is meant to be
called before a `splitn`

operation, which is expected to be evaluated
a very large number indices. Calling `level`

in such case might decrease
the total amount of work performed.