{-# LANGUAGE GADTs #-}
 
import Data.List
import Data.Map as Map
import Data.Time
 
data Model a where
	Variant  :: [(Day, a)] -> Model a
	deriving (Show)
 
day1 = fromGregorian 1987 10 17
day2 = fromGregorian 1987 10 18
day3 = fromGregorian 1987 10 19
day4 = fromGregorian 1987 10 20
day5 = fromGregorian 1987 10 21
day6 = fromGregorian 1987 10 22
 
m1 = Variant [(day1, 1), (day3, 3), (day5, 5)] :: Model Integer
m2 = Variant [(day1, 1), (day2, 2), (day4, 4), (day6, 6)] :: Model Integer
 
(Variant a) &+ (Variant b) =
	Variant $ snd $ mapAccumL (\r (d, k) -> let r' = r + k in (r', (d, r'))) 0
		$ toList $ Map.unionWith (+)
			(Map.fromDistinctAscList a)
			(Map.fromDistinctAscList b)
 
main = print $ m1 &+ m2

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