Game.LambdaHack.Core.Random

Representation of probabilities and random computations.

The Rng monad

type Rnd a = State SMGen a

The monad of computations with random generator state.

Random operations

randomR :: Integral a => (a, a) -> Rnd a

Get a random object within a (inclusive) range with a uniform distribution.

randomR0 :: Integral a => a -> Rnd a

Generate random Integral in [0, x] range.

nextRandom :: forall a. Integral a => a -> SMGen -> (a, SMGen)

Generate a random integral value in [0, x] range, where x is within Int32.

The limitation to Int32 values is needed to keep it working on signed types. In package random, a much more complex scheme is used to keep it working for arbitrary fixed number of bits.

randomWord32 :: Rnd Word32

Get a random Word32 using full range.

oneOf :: [a] -> Rnd a

Get any element of a list with equal probability.

shuffle :: Eq a => [a] -> Rnd [a]

Generates a random permutation. Naive, but good enough for small inputs.

invalidInformationCode :: Word16

Code that means the information (e.g., flavour or hidden kind index) should be regenerated, because it could not be transferred from previous playthrough (it's random in each playthrough or there was no previous playthrough).

shuffleExcept :: Vector Word16 -> Int -> [Word16] -> Rnd [Word16]

Generates a random permutation, except for the existing mapping.

frequency :: Show a => Frequency a -> Rnd a

Gen an element according to a frequency distribution.

Fractional chance

type Chance = Rational

Fractional chance.

chance :: Chance -> Rnd Bool

Give True, with probability determined by the fraction.

Casting dice scaled with level

castDice :: AbsDepth -> AbsDepth -> Dice -> Rnd Int

Cast dice scaled with current level depth.

oddsDice :: AbsDepth -> AbsDepth -> Dice -> Rnd Bool

Cast dice scaled with current level depth and return True if the results is greater than 50.

castDiceXY :: AbsDepth -> AbsDepth -> DiceXY -> Rnd (Int, Int)

Cast dice, scaled with current level depth, for coordinates.

Specialized monadic folds

foldrM :: Foldable t => (a -> b -> Rnd b) -> b -> t a -> Rnd b

foldlM' :: Foldable t => (b -> a -> Rnd b) -> b -> t a -> Rnd b

Internal operations

rollFreq :: Show a => Frequency a -> SMGen -> (a, SMGen)

Randomly choose an item according to the distribution.