CalendarInterval

Functions for working with calendar intervals.

Key ideas:

• Time is enumerable: "2018" is a collection of "2018-01/2018-12" months, "2018-01-01/2018-12-31" days etc
• Everything is an interval: "2018" is an interval of 1 year, or 12 months, or 365 days etc. A timestamp with microsecond precision is an interval 1 microsecond long
• Allen's Interval Algebra: formalism for relations between time intervals

Examples

use CalendarInterval

iex> ~I"2018-06".precision
:month

iex> CalendarInterval.next(~I"2018-12-31")
~I"2019-01-01"

iex> CalendarInterval.nest(~I"2018-06-15", :minute)
~I"2018-06-15 00:00/23:59"

iex> CalendarInterval.relation(~I"2018-01", ~I"2018-02/12")
:meets

iex> Enum.count(~I"2016-01-01/12-31")
366

References

This library is heavily inspired by "Exploring Time" talk by Eric Evans [1] where he mentioned the concept of "Countable Time" and introduced me to "Allen's Interval Algebra" [2].

• [1] https://www.youtube.com/watch?v=Zm95cYAtAa8
• [2] https://www.ics.uci.edu/~alspaugh/cls/shr/allen.html

I've also given a talk about some of these ideas at Empex NYC 2018: video, slides.

Installation

Add to mix.exs:

def deps do
  [
    {:calendar_interval, "~> 0.2.0"}
  ]
end

License

Apache 2.0