# Haskell Quiz/DayRange/Solution Jethr0

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< Haskell Quiz | DayRange(Difference between revisions)

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## Latest revision as of 10:46, 13 January 2007

-- > dayRange [1,2,3,6,7] -- "Mon-Wed, Sat, Sun" module DayRange where import Data.List (intersperse,sort) -- > dayRange [1,2,3,6,7] -- "Mon-Wed, Sat, Sun" data Weekday = Mon | Tue | Wed | Thu | Fri | Sat | Sun deriving (Show,Enum) dayRange :: [Int] -> String dayRange = sepComma . map range . map (map toWeekday) . groupBy' (\a b -> a+1 == b) . sort where sepComma = concat . intersperse ", " toWeekday x = show $ (toEnum (x-1) :: Weekday) range xs | length xs < 3 = sepComma xs | otherwise = head xs ++ "-" ++ last xs -- groupBy compares any element to the first one of the group -- groupBy' instead compares an element to the last added group element groupBy' :: (a -> a -> Bool) -> [a] -> [[a]] groupBy' f (x:xs) = gb f xs [[x]] where gb f (x:xs) ((a:as):bs) = gb f xs $ if f a x then ((x:a:as):bs) else ([x]:(a:as):bs) gb _ [] as = reverse . map reverse $ as