36 lines
724 B
Haskell
36 lines
724 B
Haskell
module DoubleStack
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where
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newtype DS a = DS (a,[a],[a])
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deriving (Eq, Ord, Read, Show)
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{- |
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Unsafe. -}
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fromListL :: [a] -> DS a
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fromListL (x:xs) = DS (x,xs,[])
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fromListL _ = undefined
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singleton :: a -> DS a
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singleton x = DS (x,[],[])
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head :: DS a -> a
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head (DS (x,_,_)) = x
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left, right :: DS a -> [a]
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left (DS (_,l,_)) = l
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right (DS (_,_,r)) = r
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pushL :: DS a -> DS a
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pushL (DS (x,xs, y:ys )) = DS (y, x:xs ,ys)
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pushL ds = ds
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pushR :: DS a -> DS a
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pushR (DS (y, x:xs ,ys)) = DS (x,xs, y:ys )
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pushR ds = ds
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cycleL :: DS a -> Maybe (DS a)
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cycleL (DS (x,xs, y:ys )) = Just $ DS (y, x:xs ,ys)
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cycleL _ = Nothing
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cycleR :: DS a -> Maybe (DS a)
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cycleR (DS (y, x:xs ,ys)) = Just $ DS (x,xs, y:ys )
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cycleR _ = Nothing
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