Getting started with Tempo

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Mix.install([
  {:ex_tempo, "~> 2.0"},
  {:tz, "~> 0.28"}
])

Calendar.put_time_zone_database(Tz.TimeZoneDatabase)

Setup

Run this cell next: every example below depends on it. It imports Tempo.Sigils, which provides the ~o sigil the examples use to write a Tempo value as ISO 8601 text — ~o"2026-06-15" is the whole day of 15 June 2026. The import brings in only sigil_o/2, no other functions.

It needs a cell of its own because Livebook compiles a whole cell before running it, so the setup cell above can't import a module that its own Mix.install/2 has yet to fetch.

import Tempo.Sigils

Time as an interval, not an instant

Every mainstream library treats a date as a scalar — an instant, usually midnight, that everyone then uses as if it were a span. Tempo makes the span the value itself: ~o"2026-06-15" is the half-open interval [2026-06-15T00:00, 2026-06-16T00:00), a year is a year-long interval, and one %Tempo{} type carries any resolution.

The ~o sigil parses the full ISO 8601 Part 1 and Part 2 grammar (plus IXDTF zone suffixes):

~o"2026-06-15"

The value knows the unit it is written to, and its span is real. Written out as an interval, a day runs from itself through itself, and an hour from itself to the next:

{Tempo.resolution(~o"2026-06-15"), Tempo.to_interval!(~o"2026-06-15"), Tempo.to_interval!(~o"2026-06-15T10")}

One type covers every resolution — a year, a month, a minute, a zoned datetime:

[~o"2026", ~o"2026-06", ~o"2026-06-15T14:30", ~o"2026-06-15T14:30[Australia/Sydney]"]

Constructing values at runtime

The sigil is for literals. For runtime data use Tempo.new/1, which accepts components in any order and validates them against the calendar, or Tempo.from_elixir/2 to bring a stdlib value in:

Tempo.new!(day: 15, year: 2026, month: 6, hour: 14, minute: 30)
Tempo.from_elixir(~U[2026-06-15 14:30:00Z])

Iteration walks the span

Because a value is a span, Enum walks into it at the next finer resolution: a month yields its days, a year its months. Even a partially-specified value like ~o"156X" — "sometime in the 1560s" — is a span you can walk:

Enum.count(~o"2026-06")
Enum.take(~o"156X", 5)

Comparison speaks Allen's algebra

Two intervals stand in exactly one of thirteen relations. Tempo.relation/2 names it; the predicates answer the everyday questions:

Tempo.relation(~o"2026-01", ~o"2026-02")

January and February meet: January ends exactly where February starts, so they share no instant and January comes before February. Allen's strict :precedes also needs a gap between them, and Tempo.Allen.precedes?/2 asks that:

{Tempo.before?(~o"2026-01", ~o"2026-02"), Tempo.Allen.precedes?(~o"2026-01", ~o"2026-02")}
Tempo.within?(~o"2026-06-01/2026-06-15", ~o"2026-06")

Set algebra

Union, intersection, difference, and complement work on any combination of values, across resolutions. The workday minus lunch is the working time:

workday = ~o"2026-06-15T09/2026-06-15T17"
lunch = ~o"2026-06-15T12/2026-06-15T13"

{:ok, working} = Tempo.difference(workday, lunch)
working

"The working time is the workday minus lunch — two spans, morning and afternoon."

Cut a free region into bookable slots:

{:ok, slots} = Tempo.IntervalSet.slots(working, ~o"PT2H")
Tempo.IntervalSet.members(slots)

Locale-aware formatting

Rendering reflects the span: a year formats as its first-through-last month, in any CLDR locale, and durations follow ECMA-402 conventions:

{Tempo.to_string!(~o"2026"), Tempo.to_string!(~o"2026-06")}
{Tempo.to_string!(~o"P3DT2H"), Tempo.to_string!(~o"P3DT2H", format: :short)}
Tempo.to_string!(~o"P1Y6M", locale: :de)

And when a value puzzles you, ask it to explain itself:

Tempo.explain(~o"156X") |> IO.puts()

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