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{-# LANGUAGE UndecidableInstances #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
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module Xanthous.Random
( Choose(..)
, ChooseElement(..)
, Weighted(..)
, evenlyWeighted
, weightedBy
, subRand
, chance
) where
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import Xanthous.Prelude
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import Data.List.NonEmpty (NonEmpty(..))
import Control.Monad.Random.Class (MonadRandom(getRandomR, getRandom))
import Control.Monad.Random (Rand, evalRand, mkStdGen, StdGen)
import Data.Random.Shuffle.Weighted
import Data.Random.Distribution
import Data.Random.Distribution.Uniform
import Data.Random.Distribution.Uniform.Exclusive
import Data.Random.Sample
import qualified Data.Random.Source as DRS
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instance {-# INCOHERENT #-} (Monad m, MonadRandom m) => DRS.MonadRandom m where
getRandomWord8 = getRandom
getRandomWord16 = getRandom
getRandomWord32 = getRandom
getRandomWord64 = getRandom
getRandomDouble = getRandom
getRandomNByteInteger n = getRandomR (0, 256 ^ n)
class Choose a where
type RandomResult a
choose :: MonadRandom m => a -> m (RandomResult a)
newtype ChooseElement a = ChooseElement a
instance MonoFoldable a => Choose (ChooseElement a) where
type RandomResult (ChooseElement a) = Maybe (Element a)
choose (ChooseElement xs) = do
chosenIdx <- getRandomR (0, olength xs - 1)
let pick _ (Just x) = Just x
pick (x, i) Nothing
| i == chosenIdx = Just x
| otherwise = Nothing
pure $ ofoldr pick Nothing $ zip (toList xs) [0..]
instance MonoFoldable a => Choose (NonNull a) where
type RandomResult (NonNull a) = Element a
choose
= fmap (fromMaybe (error "unreachable")) -- why not lol
. choose
. ChooseElement
. toNullable
instance Choose (NonEmpty a) where
type RandomResult (NonEmpty a) = a
choose = choose . fromNonEmpty @[_]
instance Choose (a, a) where
type RandomResult (a, a) = a
choose (x, y) = choose (x :| [y])
newtype Weighted w t a = Weighted (t (w, a))
evenlyWeighted :: [a] -> Weighted Int [] a
evenlyWeighted = Weighted . itoList
weightedBy :: Functor t => (a -> w) -> t a -> Weighted w t a
weightedBy weighting xs = Weighted $ (weighting &&& id) <$> xs
instance (Num w, Ord w, Distribution Uniform w, Excludable w) => Choose (Weighted w [] a) where
type RandomResult (Weighted w [] a) = Maybe a
choose (Weighted ws) = sample $ headMay <$> weightedSample 1 ws
instance (Num w, Ord w, Distribution Uniform w, Excludable w) => Choose (Weighted w NonEmpty a) where
type RandomResult (Weighted w NonEmpty a) = a
choose (Weighted ws) =
sample
$ fromMaybe (error "unreachable") . headMay
<$> weightedSample 1 (toList ws)
subRand :: MonadRandom m => Rand StdGen a -> m a
subRand sub = evalRand sub . mkStdGen <$> getRandom
-- | Has a @n@ chance of returning 'True'
--
-- eg, chance 0.5 will return 'True' half the time
chance
:: (Num w, Ord w, Distribution Uniform w, Excludable w, MonadRandom m)
=> w
-> m Bool
chance n = choose $ weightedBy (bool 1 (n * 2)) bools
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bools :: NonEmpty Bool
bools = True :| [False]
