42 lines
1.2 KiB
Haskell
42 lines
1.2 KiB
Haskell
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data Weekday = Monday | Tuesday | Wednesday | Thursday | Friday | Saturday | Sunday
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deriving (Show, Eq, Ord, Enum)
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data Month = January | February | March | April | May | June | July | August | September | October | November | December
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deriving (Show, Eq, Ord, Enum)
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type Day = Int
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type Year = Int
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data Date = Date Year Month Day Weekday
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deriving (Show, Eq, Ord)
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nextWeekday :: Weekday -> Weekday
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nextWeekday Sunday = Monday
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nextWeekday d = succ d
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nextMonth :: Month -> Month
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nextMonth December = January
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nextMonth m = succ m
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getDays :: Month -> Year -> Int
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getDays m y
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| elem m [September, April, June, November] = 30
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| m == February = if rem y 4 == 0 && if rem y 100 == 0 && rem y 400 /= 0 then False else True
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then 29 else 28
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| otherwise = 31
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nextDate :: Date -> Date
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nextDate (Date y m d wd)
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| d < getDays m y = Date y m (d+1) (nextWeekday wd)
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| m == December = Date (y+1) January 1 (nextWeekday wd)
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| otherwise = Date y (nextMonth m) 1 (nextWeekday wd)
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daysTwentieth :: [Date]
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daysTwentieth = takeWhile (\(Date y _ _ _) -> y /=2001) (dates start)
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where
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dates d = d:dates (nextDate d)
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start = Date 1901 January 1 Tuesday
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e019 = length . filter (\(Date y m d wd) -> d == 1 && wd == Sunday) $ daysTwentieth
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