diff options
Diffstat (limited to 'users/glittershark/xanthous/src/Xanthous/Random.hs')
-rw-r--r-- | users/glittershark/xanthous/src/Xanthous/Random.hs | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/users/glittershark/xanthous/src/Xanthous/Random.hs b/users/glittershark/xanthous/src/Xanthous/Random.hs new file mode 100644 index 000000000000..6d34109df7f8 --- /dev/null +++ b/users/glittershark/xanthous/src/Xanthous/Random.hs @@ -0,0 +1,118 @@ +-------------------------------------------------------------------------------- +{-# LANGUAGE UndecidableInstances #-} +{-# OPTIONS_GHC -fno-warn-orphans #-} +-------------------------------------------------------------------------------- +module Xanthous.Random + ( Choose(..) + , ChooseElement(..) + , Weighted(..) + , evenlyWeighted + , weightedBy + , subRand + , chance + , chooseSubset + ) where +-------------------------------------------------------------------------------- +import Xanthous.Prelude +-------------------------------------------------------------------------------- +import Data.List.NonEmpty (NonEmpty(..)) +import Control.Monad.Random.Class (MonadRandom(getRandomR, getRandom)) +import Control.Monad.Random (Rand, evalRand, mkStdGen, StdGen) +import Data.Functor.Compose +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 +-------------------------------------------------------------------------------- + +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)) + deriving (Functor, Foldable) via (t `Compose` (,) w) + +instance Traversable t => Traversable (Weighted w t) where + traverse f (Weighted twa) = Weighted <$> (traverse . traverse) f twa + +evenlyWeighted :: [a] -> Weighted Int [] a +evenlyWeighted = Weighted . itoList + +-- | Weight the elements of some functor by a function. Larger values of 'w' per +-- its 'Ord' instance will be more likely to be generated +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 + +-- | Choose a random subset of *about* @w@ of the elements of the given +-- 'Witherable' structure +chooseSubset :: ( Num w, Ord w, Distribution Uniform w, Excludable w + , Witherable t + , MonadRandom m + ) => w -> t a -> m (t a) +chooseSubset = filterA . const . chance + +-------------------------------------------------------------------------------- + +bools :: NonEmpty Bool +bools = True :| [False] |