Add 'users/glittershark/xanthous/' from commit '53b56744f4'

git-subtree-dir: users/glittershark/xanthous
git-subtree-mainline: 91f53f02d8
git-subtree-split: 53b56744f4

users/glittershark/xanthous/src/Xanthous/Random.hs

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+--------------------------------------------------------------------------------
+{-# LANGUAGE UndecidableInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+--------------------------------------------------------------------------------
+module Xanthous.Random
+  ( Choose(..)
+  , ChooseElement(..)
+  , Weighted(..)
+  , evenlyWeighted
+  , weightedBy
+  , subRand
+  , chance
+  ) 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.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))
+
+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
+
+--------------------------------------------------------------------------------
+
+bools :: NonEmpty Bool
+bools = True :| [False]