Haskell:
Calculating a date in the future or past

import Data.Time

-- Add days to the current date
addDaysToCurrent :: Integer -> IO Day
addDaysToCurrent n = do
  today <- getCurrentTime
  timezone <- getCurrentTimeZone
  let localToday = utcToLocalTime timezone today
  return $ addDays n (localDay localToday)

-- Usage: addDaysToCurrent 10 to add 10 days to the current date

-- Calculate a future or past date by adding or subtracting days
calculateDate :: Day -> Integer -> Day
calculateDate start n = addDays n start

-- Usage example:
-- let futureDate = calculateDate (fromGregorian 2023 1 1) 90

-- To handle months and years, we use `addGregorianMonthsClip` and `addGregorianYearsClip`
calculateDateMonths :: Day -> Integer -> Day
calculateDateMonths start n = addGregorianMonthsClip n start

-- Usage:
-- let futureMonth = calculateDateMonths (fromGregorian 2023 1 1) 2

-- Output a date in the format YYYY-MM-DD
printFormattedDate :: Day -> IO ()
printFormattedDate date = putStrLn $ formatTime defaultTimeLocale "%F" date

-- Usage:
-- printFormattedDate futureDate