Arithmetic and comparison

Add a duration to an instant to get a later instant, and take one instant from another to get the time between them:

Instant + Duration, Duration + Instant and Instant - Duration give an Instant of the instant's own named type, so you don't build it again.
Instant - Instant gives the Duration between them, which is negative when the second is later.
Duration + Duration and Duration - Duration give a Duration.

As with numbers, both sides must be the same type after widening, or one must be a literal. Two durations of the same named type give a plain Duration.

Instants, dates and durations order with <, <=, > and >=, and compare with == on the timeline, so 12:00Z equals 13:00+01:00.

A CalendarDate has no clock time, so a Duration doesn't move it. It moves by calendar days with temporal.add_days. A ZonedTime moves on its calendar the same way, or through its instant. *, / and % don't take time values.

example

type DueAt = Instant {}type ReminderNotice = Duration {    min: 1m    max: 7d}type Lateness = Duration {}/// When to send a reminder: the notice before the due time. Taking a/// duration from a `DueAt` gives a `DueAt`.function reminder_time(due_at: DueAt, notice: ReminderNotice) -> DueAt {    return due_at - notice}/// How late something done at `done_at` was: negative when it was early.function lateness(due_at: DueAt, done_at: DueAt) -> Lateness {    return Lateness(done_at - due_at)}test "a duration moves an instant and keeps its type" {    assert reminder_time("2026-10-25T09:00:00Z", 30m) == "2026-10-25T08:30:00Z"    assert lateness("2026-10-25T09:00:00Z", "2026-10-25T11:15:00Z") == 135m    assert lateness("2026-10-25T09:00:00Z", "2026-10-25T08:00:00Z") < 0s}test "instants compare on the timeline" {    assert DueAt("2026-10-25T12:00:00Z") == DueAt("2026-10-25T13:00:00+01:00")    assert DueAt("2026-10-25T12:00:00Z") < DueAt("2026-10-25T12:00:00.001Z")}