DateTime

The following functions operate on the type DateTime representing a Date together with a Time. The definition is

type DateTime {
  date : Date,
  time : Time
}

Note that a DateTime does not include a time zone and therefore does not correspond to a unique Instant on the global timeline. It is therefore not possible to add a Duration to a DateTime because the result is undefined. For example, the result of adding 24 hours to 2020-10-25 01:00 could be either 2020-10-26 01:00 or 2020-10-26 00:00 depending on whether the time zone is America/New_York or Europe/Copenhagen, respectively, because the two regions observe daylight saving time in different periods.

If you need to perform arithmetic on calendar dates together with time of day, use the zoned time and date functions.

DateTime::addPeriod : Period -> DateTime -> DateTime

Add a Period to the underlying calendar date. The time component is unchanged.

This function is partial and fails if the resulting date would be out of range; see Date::fromComponents.

Examples

val a = DateTime::addPeriod
          (Period::from 0 0 1)
          (DateTime {
            date = Date::from 2020 10 25,
            time = Time::from 1 0 0 0
          })
//    = DateTime {
//        date = Date::from 2020 10 26,
//        time = Time::from 1 0 0 0
//      }