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Last active Feb 5, 2021
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import Data.Sequence (Seq (Empty, (:<|), (:|>)))
import qualified Data.Sequence as Seq
newtype RunLength a = RunLength (Seq.Seq (Int, a))
deriving (Eq, Show)
singleton :: a -> RunLength a
singleton a = RunLength (Seq.singleton (1, a))
runLengthToList :: RunLength a -> [a]
runLengthToList (RunLength runs) = foldMap (uncurry replicate) runs
instance Eq a => Semigroup (RunLength a) where
RunLength (as :|> (countA, a)) <> RunLength ((countB, b) :<| bs)
| a == b = RunLength ((as :|> (countA + countB, a)) <> bs)
RunLength as <> RunLength bs = RunLength (as <> bs)
instance Eq a => Monoid (RunLength a) where
mempty = RunLength Empty
runLengthFromList :: Eq a => [a] -> RunLength a
runLengthFromList = foldMap singleton
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