time-recurrence is a Haskell library for working with recurring date/times. The iCalendar Specifcation (RFC 5545) is used for inspiration of this library, however the library does not make an effort to track the RFC at all times. A future Data.Time.Recurrence.RFC5545 library would be a useful add-on for those in need of strict RFC compliance. Examples: > parse822Time :: String -> UTCTime > parse822Time = ... > nov1996 = parse822Time "Tue, 05 Nov 1996 09:00:00 -0400" > mar1997 = parse822Time "Mon, 10 Mar 1997 09:00:00 -0400" > sep1997 = parse822Time "Tue, 02 Sep 1997 09:00:00 -0400" > oct1997 = parse822Time "Fri, 10 Oct 1997 00:00:00 -0400" > dec1997 = parse822Time "Wed, 24 Dec 1997 00:00:00 -0400" > jan1998 = parse822Time "Thu, 01 Jan 1998 09:00:00 -0400" > jan2000 = parse822Time "Mon, 31 Jan 2000 09:00:00 -0400" Daily for 10 occurrences: > take 10 $ recur daily `begin` sep1997 Daily until Dec. 24, 1997: > takeWhile (<= dec1997) $ recur daily `begin` sep1997 Every other day - forever: > recur daily `by` 2 `begin` sep1997 Every 10 days, 5 occurrences: > take 5 $ recur daily `by` 10 `begin` sep1997 Every day in January, for 3 years: > takeWhile (<= jan2000) $ recur yearly `starting` jan1998 $ > enumMonths [January] >=> > filterWeekDays [Monday .. Sunday] > takeWhile (<= jan2000) $ recur daily `starting` jan1998 $ > enumMonths [January] Weekly for 10 occurrences: > take 10 $ recur weekly `begin` sep1997 Weekly until Dec. 24, 1997: > takeWhile (<= dec1997) $ recur weekly `withStartOfWeek` Sunday `begin` sep1997 Every other week - forever: > recur weekly `by` 2 `begin` sep1997 Weekly on Tuesday and Thursday for five weeks: > takeUntil (<= oct1997) $ recur weekly `withStartOfWeek` Sunday `starting` sep1997 $ > enumWeekDaysInWeek [Tuesday, Thursday] or > take 10 $ recur weekly `withStartOfWeek` Sunday `starting` sep1997 $ > enumWeekDaysInWeek [Tuesday, Thursday] Every other week (Monday, Wednesday, Firday) until Dec. 24, 1997: > takeWhile (<= dec1997) $ recur weekly `withStartOfWeek` Sunday `by` 2 `starting` sep1997$ > enumWeekDaysInWeek [Monday, Wednesday, Friday] >=> > Every other week on Tuesday and Thursday, for 8 occurrences: > take 8 $ recur weekly `withStartOfWeek` Sunday `by` 2 `starting` sep1997 $ > enumWeekDaysInWeek [Tuesday, Thursday] Monthly on the first Friday for 10 occurrences: > take 10 $ recur monthly `starting` sep1997 $ > enumWeekDaysInMonth [Friday] >=> > nthWeekDayInMonth [1] Monthly on the first Friday until Dec. 24, 1997 > takeWhile (<= dec1997) $ recur monthly `starting` sep1997 $ > enumWeekDaysInMonth [Friday] >=> > nthWeekDayInMonth [1] Every other month on the first and last Sunday of the month for 10 occurrences: > take 10 $ recur monthly `by` 2 `starting` sep1997 $ > enumWeekDaysInMonth [Sunday] >=> > nthWeekDayInMonth [1,-1] Monthly on the second-to-last Monday of the month for 6 months: > take 6 $ recur monthly `starting` sep1997 $ > enumWeekDaysInMonth [Monday] >=> > nthWeekDayInMonth [-2] Monthly on the third-to-last day of the month, forever: > recur monthly `starting` sep1997 $ enumDays [-3] Monthly on the 2nd and 15th of the month for 10 occurrences: > take 10 $ recur monthly `starting` sep1997 $ enumDays [2,15] Monthly on the first and last day of the month for 10 occurrences: > take 10 $ recur monthly `starting` sep1997 $ enumDays [1,-1] Every 18 months on the 10th thru 15th of the month for 10 occurrences: > take 10 $ recur monthly `by` 18 `starting` sep1997 $ enumDays [10 .. 15] Every Tuesday, every other month: > recur monthly `by` 2 `starting` sep1997 $ enumWeekDaysInMonth [Tuesday] Yearly in June and July for 10 occurrences: > take 10 $ recur yearly `starting` sep1997 $ enumMonths [June, July] Every other year on January thru March for 10 occurrences: > take 10 $ recur yearly `by` 2 `starting` mar1997 $ > enumMonths [January .. March] >=> > enumWeekDaysInMonth [Monday .. Sunday] Every third year on the 1st, 100th, and 200th day for 10 occurrences: > take 10 $ recur yearly `by` 3 `starting` sep1997 $ > enumYearDays [1,100,200] Every 20th Monday of the year, forever: > recur monthly `starting` sep1997 $ > enumWeekDaysInMonth [Monday] >=> > nthWeekDay [20] Monday of week number 20, forever: > recur yearly `starting` mar1997 $ > enumWeekNumbers [20] >=> > filterWeekDays [Monday] or > recur weekly `starting` mar1997 $ > filterWeekNumbers [20] >=> > filterWeekDays [Monday] Every Thursday in March, forever: > recur yearly `starting` mar1997 $ > enumMonths [March] >=> > enumWeekDaysInMonth [Thrusday] Every Thursday, but only during June thru August, forever: > recur yearly `starting` mar1997 $ > enumMonths [June .. August] >=> > enumWeekDaysInMonth [Thursday] Firday the 13th, Forever: > recur monthly `starting` sep1997 $ enumDays [13] >=> filterWeekDays [Friday] The first Saturday that follows the first Sunday of the month, forever: > recur monthly sep1997 $ > enumDays [7 .. 13] >=> > filterWeekDays [Saturday] U.S. Presidential Election Day: Every 4 years, the first Tuesday after a Monday in November, forever: > recur yearly `by` 4 `starting` nov1996 $ > enumMonths [November] >=> > enumDays [2 .. 8] >=> > filterWeekDays [Tuesday] The third instance into the month of one of Tuesday, Wednesday, or Thursday, for the next 3 months. > take 3 $ recur monthly `starting` sep1997 $ > enumWeekDaysInMonth [Tuesday .. Thursday] >=> > nthWeekDayInMonth [3] The second-to-last weekday of the month: > recur monthly `starting` sep1997 $ > enumWeekDaysOfMonth [Monday .. Friday] >=> > nthWeekDayOfMonth [-2] Every 3 hours from 9:00 AM to 5:00 PM on a specific day: > takeWhile (<= addSeconds sep1997 (8 * oneHour)) $ > recur hourly `by` 3 `begin` sep1997 Every 15 minutes for 6 occurrences: > take 6 $ recur minutely `by` 15 `begin` sep1997 Every hour and a hald for 4 occurrences: > take 4 $ recur minutely `by` 90 `begin` sep1997 Every 20 minutes from 9:00 AM to 4:40 PM every day: > recur daily `starting` sep1997 $ > enumHours [9 .. 16] >=> > enumMinutes [0,20,40] or > recur minutely `by` 20 `starting` sep1997 $ enumHours [9 .. 16] The following two examples will generate different results due to changes in the start of the week. > take 4 $ recur weekly `by` 2 `withStartOfWeek` Monday $ > enumWeekDaysInWeek [Tuesday,Sunday] vs > take 4 $ recur weekly `by` 2 `withStartOfWeek` Sunday $ > enumWeekDaysInWeek [Tuesday,Sunday] An example where an invalid date (Feb. 30) is ignored: > take 5 $ recur monthly `starting` jan2000 $ enumDays [15,30] The 15th and the 30th of the month, forever: > recur monthly `starting` sep1997 $ enumDays [15,30] The 15th and the 30th of the month, but only during the work week: > recur monthly `starting` sep1997 $ > enumDays [15,30] >=> > filterWeekDays [Monday .. Friday]