return nil, errNotImplemented
	}
	return FromTimestamp(t.Add(duration)), nil
}

// dateDiff computes the difference between two times in terms of the
// `timePart` which can be years, months, days, hours, minutes or
// seconds. For difference in years, months or days, the time part,
// including timezone is ignored.
func dateDiff(timePart string, ts1, ts2 time.Time) (*Value, error) {
	if ts2.Before(ts1) {