Haskell Quiz/DayRange/Solution Jethr0
< Haskell Quiz | DayRange
Jump to navigation
Jump to search
Revision as of 18:00, 16 December 2006 by JohannesAhlmann (talk | contribs) (using a datatype, added type declarations)
-- > 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) . groupAscend . sort
where sepComma = concat . intersperse ", "
toWeekday x = show $ (toEnum (x-1) :: Weekday)
range xs | length xs < 3 = sepComma xs
| otherwise = head xs ++ "-" ++ last xs
-- group list of numbers into directly ascending subgroups
groupAscend :: [Int] -> [[Int]]
groupAscend (x:xs) = together $ foldl ascend ([],[x]) xs
where ascend (done,curr) e = if e == (last curr)+1 then (done, curr++[e])
else (done++[curr], [e])
together (a,b) = a++[b]