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 $ starting sep1997 $ recur daily Daily until Dec. 24, 1997: > takeWhile (<= dec1997) $ starting sep1997 $ recur daily Every other day - forever: > starting sep1997 $ recur daily `by` 2 Every 10 days, 5 occurrences: > take 5 $ starting sep1997 $ recur daily `by` 10 Every day in January, for 3 years: > takeWhile (<= jan2000) $ starting jan1998 $ > recur yearly > >==> enum (Months [January]) > >==> filter (WeekDays [Monday .. Sunday]) > takeWhile (<= jan2000) $ starting jan1998 $ > recur daily > >==> enum (Months [January]) Weekly for 10 occurrences: > take 10 $ starting sep1997 $ recur weekly Weekly until Dec. 24, 1997: > takeWhile (<= dec1997) $ starting sep1997 $ > recur weekly `withStartOfWeek` Sunday Every other week - forever: > starting sep1997 $ recur weekly `by` 2 Weekly on Tuesday and Thursday for five weeks: > takeUntil (<= oct1997) $ starting sep1997 $ > recur weekly `withStartOfWeek` Sunday > >==> enum (WeekDaysInWeek [Tuesday, Thursday]) or > take 10 $ starting sep1997 $ > recur weekly `withStartOfWeek` Sunday > >==> enum (WeekDaysInWeek [Tuesday, Thursday]) Every other week (Monday, Wednesday, Firday) until Dec. 24, 1997: > takeWhile (<= dec1997) $ starting sep1997 $ > recur weekly `withStartOfWeek` Sunday `by` 2 > >==> enum (WeekDaysInWeek [Monday, Wednesday, Friday]) > Every other week on Tuesday and Thursday, for 8 occurrences: > take 8 $ starting sep1997 $ > recur weekly `by` 2 `withStartOfWeek` Sunday > >==> enum (WeekDaysInWeek [Tuesday, Thursday]) Monthly on the first Friday for 10 occurrences: > take 10 $ starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Friday]) > >==> select (WeekDaysInMonth [1]) Monthly on the first Friday until Dec. 24, 1997 > takeWhile (<= dec1997) $ starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Friday]) > >==> select (WeekDaysInMonth [1]) Every other month on the first and last Sunday of the month for 10 occurrences: > take 10 $ starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Sunday]) > >==> select (WeekDaysInMonth [1,-1]) Monthly on the second-to-last Monday of the month for 6 months: > take 6 $ starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Monday]) > >==> select (WeekDaysInMonth [-2]) Monthly on the third-to-last day of the month, forever: > starting sep1997 $ > recur monthly > >==> enum (Days [-3]) Monthly on the 2nd and 15th of the month for 10 occurrences: > take 10 $ starting sep1997 $ > recur monthly > >==> enum (Days [2,15]) Monthly on the first and last day of the month for 10 occurrences: > take 10 $ starting sep1997 $ > recur monthly > >==> enum (Days [1,-1]) Every 18 months on the 10th thru 15th of the month for 10 occurrences: > take 10 $ starting sep1997 $ > recur monthly > >==> enum (Days [10 .. 15]) Every Tuesday, every other month: > starting sep1997 $ > recur monthly `by` 2 > >==> enum (WeekDaysInMonth [Tuesday]) Yearly in June and July for 10 occurrences: > take 10 $ starting sep1997 $ > recur yearly > >==> enum (Months [June, July]) Every other year on January thru March for 10 occurrences: > take 10 $ starting mar1997 $ > recur yearly `by` 2 > >==> enum (Months [January .. March]) > >==> enum (WeekDaysInMonth [Monday .. Sunday]) Every third year on the 1st, 100th, and 200th day for 10 occurrences: > take 10 $ starting sep1997 $ > recur yearly `by` 3 > >==> enum (YearDays [1,100,200]) Every 20th Monday of the year, forever: > starting sep1997 $ > recur montly > >==> enum (WeekDaysInMonth [Monday]) > >==> select (WeekDays [20]) Monday of week number 20, forever: > starting mar1997 $ > recur yearly > >==> enum (Weeks [20]) > >==> filter (WeekDays [Monday]) or > starting mar1997 $ > recur weekly > >==> filter (Weeks [20]) > >==> filter (WeekDays [Monday]) Every Thursday in March, forever: > starting mar1997 $ > recur yearly > >==> enum (Months [March]) > >==> enum (WeekDaysInMonth [Thursday]) Every Thursday, but only during June thru August, forever: > starting mar1997 $ > recur yearly > >==> enum (Months [June .. August]) > >==> enum (WeekDaysInMonth [Thursday]) Friday the 13th, Forever: > starting sep1997 > recur monthly > >==> enum (Days [13]) > >==> filter (WeekDays [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: > starting nov1996 $ > recur yearly `by` 4 > >==> enum (Months [November]) > >==> enum (Days [2 .. 8]) > >==> filter (WeekDays [Tuesday]) The third instance into the month of one of Tuesday, Wednesday, or Thursday, for the next 3 months. > take 3 $ starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Tuesday .. Thursday]) > >==> select (WeekDaysInMonth [3]) The second-to-last weekday of the month: > starting sep1997 $ > recur monthly > >==> enum (WeekDaysInMonth [Monday .. Friday]) > >==> select (WeekDaysInMonth [-2]) Every 3 hours from 9:00 AM to 5:00 PM on a specific day: > takeWhile (<= addSeconds sep1997 (8 * oneHour)) $ > starting sep1997 $ > recur hourly `by` 3 Every 15 minutes for 6 occurrences: > take 6 $ starting sep1997 $ > recur minutely `by` 15 Every hour and a half for 4 occurrences: > take 4 $ starting sep1997 $ recur minutely `by` 90 Every 20 minutes from 9:00 AM to 4:40 PM every day: > staring sep1997 $ > recur daily $ > >==> enum (Hours [9 .. 16]) > >==> enum (Minutes [0,20,40]) or > starting sep1997 $ > recur minutely `by` 20 > >==> enum (Hours [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 > >==> enum (WeekDaysInWeek [Tuesday, Sunday]) vs > take 4 $ > recur weekly `by` 2 `withStartOfWeek` Sunday > >==> enum (WeekDaysInWeek [Tuesday, Sunday]) An example where an invalid date (Feb. 30) is ignored: > take 5 $ starting jan2000 $ > recur monthly > >==> enum (Days [15,30]) The 15th and the 30th of the month, forever: > starting sep1997 $ > recur monthly > >==> enum (Days [15,30]) The 15th and the 30th of the month, but only during the work week: > starting sep1997 $ > recur monthly > >==> enum (Days [15,30]) > >==> filter (WeekDays [Monday .. Friday])