CalendarArithmetic

CalendarArithmetic :: # (opaque)

Gregorian arithmetic. No timezone resolution or recurrence is implied.

Example

For an invoice due one month after January 31, Clamp chooses February's last day. Reject instead returns InvalidDestination; Carry carries excess days into the following month. Recurrence rules use different skip semantics.

import time.GregorianDate
import time.CalendarArithmetic
import time.CalendarDelta

expect {
    issued = GregorianDate.from_fields({ year: 2025, month: 1, day: 31 })?
    due = CalendarArithmetic.shift_day(issued, CalendarDelta.months(1), Clamp)?
    GregorianDate.to_fields(due) == { year: 2025, month: 2, day: 28 }
}

Examples assume a package dependency named time.

shift_day : GregorianDate, CalendarDelta, Policy -> Try(GregorianDate, [OutOfRange, InvalidDestination(Fields), ..])

Policy : [Reject, Clamp, Carry]