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Scheduled Merge Sort
{-# LANGUAGE BangPatterns #-}
module ScheduledMergeSort where
import Control.DeepSeq
newtype Schedule a = Schedule [[a]] deriving Show
data Segment a = Segment [a] (Schedule a) deriving Show
data MergeSort a = MergeSort Int [Segment a] deriving Show
instance NFData (Segment a)
mrg :: Ord a => [a] -> [a] -> [a]
mrg [] ys = ys
mrg xs [] = xs
mrg xs@(x:xs') ys@(y:ys')
| x <= y = x:mrg xs' ys
| otherwise = y:mrg xs ys'
exec1 :: Schedule a -> Schedule a
exec1 (Schedule []) = Schedule []
exec1 (Schedule ([]:sched)) = exec1 (Schedule sched)
exec1 (Schedule ((_:xs):sched)) = Schedule (xs:sched)
exec2 :: Segment a -> Segment a
exec2 (Segment xs sched) = Segment xs sched2
where
!sched1 = exec1 sched
!sched2 = exec1 sched1
empty :: MergeSort a
empty = MergeSort 0 []
add :: Ord a => a -> MergeSort a -> MergeSort a
add x (MergeSort size segs) = MergeSort (size + 1) (map exec2 $!! segs')
where
segs' = addSeg [x] segs size []
addSeg :: Ord a => [a] -> [Segment a] -> Int -> [[a]] -> [Segment a]
addSeg xs segs size rsched
| size `mod` 2 == 0 = Segment xs (Schedule (reverse rsched)) : segs
| otherwise = addSeg xs'' segs' (size `div` 2) (xs'':rsched)
where
(Segment xs' (Schedule [])) : segs' = segs
xs'' = mrg xs xs'
sort :: Ord a => MergeSort a -> [a]
sort (MergeSort _ segs) = mrgAll [] segs
where
mrgAll xs [] = xs
mrgAll xs (Segment xs' _ : segs') = mrgAll (mrg xs xs') segs'
infixl 0 >-
(>-) :: a -> (a -> b) -> b
a >- f = f a
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