49 lines
1.3 KiB
Haskell
49 lines
1.3 KiB
Haskell
module Stream (
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Stream(..)
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, append
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, empty
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, fromList
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, infinite
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, merge
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) where
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import Tree (Tree(..), Structure(..))
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data Stream a = Stream [(a, Stream a)] deriving Show
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instance Functor Stream where
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fmap f (Stream pairs) =
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Stream $ (\(a, stream) -> (f a, fmap f stream)) <$> pairs
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instance Tree Stream where
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getStructure (Stream []) = Leaf
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getStructure (Stream pairs) =
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Node $ (\(s, stream) -> (s, getStructure stream)) <$> pairs
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empty :: Stream a
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empty = fromList []
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append :: Stream a -> Stream a -> Stream a
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append (Stream []) b = b
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append (Stream pairs) b =
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Stream $ (\(a, stream) -> (a, stream `append` b)) <$> pairs
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fromList :: [a] -> Stream a
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fromList [] = Stream []
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fromList (pair:pairs) = Stream [(pair, fromList pairs)]
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infinite :: a -> Stream a
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infinite a = Stream [(a, infinite a)]
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merge :: Eq a => Stream a -> Stream a -> Stream a
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merge (Stream aPairs) (Stream bPairs) = Stream $ foldl mergeOrAdd aPairs bPairs
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where
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openAt _ l [] = (l, [])
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openAt p up l@(x:xs) = if p x then (up, l) else openAt p (x:up) xs
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zipUp ([], l) = l
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zipUp (x:xs, l) = zipUp (xs, x:l)
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mergeOrAdd accumulator (b, bStream) = zipUp $
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case openAt ((== b) . fst) [] accumulator of
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(up, []) -> (up, [(b, bStream)])
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(up, (x, xStream):down) -> (up, (x, merge xStream bStream):down)
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