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Implement stable merging of Streams

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Tissevert 2019-05-03 19:07:40 +02:00
parent a34e1e8806
commit 06ec115c88
1 changed files with 12 additions and 0 deletions
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12
src/Stream.hs
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@ -18,6 +18,18 @@ fromList (pair:pairs) = Stream [(pair, fromList pairs)]
infinite :: a -> Stream a
infinite a = Stream [(a, infinite a)]
merge :: Eq a => Stream a -> Stream a -> Stream a
merge (Stream aPairs) (Stream bPairs) = Stream $ foldl mergeOrAdd aPairs bPairs
where
openAt _ l [] = (l, [])
openAt p up l@(x:xs) = if p x then (up, l) else openAt p (x:up) xs
zipUp ([], l) = l
zipUp (x:xs, l) = zipUp (xs, x:l)
mergeOrAdd accumulator (b, bStream) = zipUp $
case openAt ((== b) . fst) [] accumulator of
(up, []) -> (up, [(b, bStream)])
(up, (x, xStream):down) -> (up, (x, merge xStream bStream):down)
showTree :: Show a => Stream a -> String
showTree = intercalate "\n" . getLines
where