ToolShed.System.Random

AUTHOR

Dr. Alistair Ward

DESCRIPTION

Utilities related to random-numbers.

Functions

randomGens :: RandomGen randomGen => randomGen -> [randomGen]

Constructs an infinite list of independent random-generators.

shuffle :: RandomGen randomGen => randomGen -> [a] -> [a]

• Shuffles the specified finite list.
• The resulting list has the same length and constituents as the original; only the order has changed.
• CAVEAT: the implementation zips a list of integers, with the specified polymorphic list, then sorts it, but when identical random integers are generated, the sort-algorithm being stable always return the corresponding items in their original order. The shuffle is therefore imperfect, but on a 64-bit machine, it would need such a large list of items, for the probability of randomly generating two identical integers, to be significant, that sort probably wouldn't return in a reasonable time anyway. Ideally, it would be amended to use an unstable sort-algorithm.

generateSelection :: RandomGen randomGen => randomGen -> [a] -> [a]

• Generate an infinite list of items, each randomly selected from the specified finite list.
• CAVEAT: because the selections are made non-destructively, duplicates may be returned; cf. shuffle.

generateSelectionFromBounded :: (RandomGen randomGen, Bounded a, Random a) => randomGen -> [a]

• Generate an infinite list of items, each randomly selected, from the specified finite list of bounded items.
• Because the selections are made non-destructively, duplicates may be returned.
• E.g. (generateSelectionFromBounded fmap System.Random.getStdGen) :: IO [Bool] .

select :: RandomGen randomGen => randomGen -> [a] -> a

Return a random element from the specified list.