Documentation

Kronos is a tool for calculating date/times. It is meant to give a concrete date for questions like "When is the 2nd Monday of June?", or "What was the 3rd to last day-of-the-week of past February?".

To answer these questions kronos composes TimeSequence iterators. These are infinite sequences into the past and the future which you can pin to a particular instant and get resulting time Ranges.

Example

Lets first define a TimeSequence that represents any and all Mondays. Then use it to get an iterator of all future Mondays from a specific t0 instant onward.

// Reference time: Tuesday, 5th Feb 2019
let t0 = chrono::NaiveDate::from_ymd(2019, 2, 5)
  .and_hms(0, 0, 0);

// A sequence for *Mondays*
let mondays = kronos::Weekday(1);

// First Monday after t0 reference time
mondays.future(&t0).next()

Ranges

The previous example would return a Range which represents an open-ended time interval [start, end). Ranges also have a Grain that specifies the resolution of the start and end instants.

Examples of a Range could be Aug 26th 2018.

• It has a resolution of Grain::Day,
• starts on 2018/08/26 00:00:00,
• ends on 2018/08/27 00:00:00

Composing TimeSequences

Basic sequences

Some simple TimeSequences can be built almost out of thin air. For example:

• Weekday(2) a sequence for Tuesdays.
• Month(6) a sequence for all June months.
• Grains(Grain::Day) a sequence to iterate over days.

Composite sequences

More comples TimeSequences can be created by combining other sequences. For example:

• NthOf(2, Weekday(1), Month(6)) creates a sequence for "the second Mondays of June".
• LastOf(1, Weekend, Grains(Grain::Year)) for "last weekend of the year".
• Intersect(Weekday(1), NthOf(28, Grains(Grain::Day), Grains(Grains::Month))) for "all Monday 28th".

Other compositions allow unions, intersections, intervals, exceptions, etc. Please check each module's tests for examples on how to use them.

References

• http://homes.cs.washington.edu/~kentonl/pub/ladz-acl.2014.pdf

• https://github.com/wit-ai/duckling_old/blob/6b7e2e1bdbd50299cee4075ff48d7323c05758bc/src/duckling/time/pred.clj#L57-L72
• https://github.com/wit-ai/duckling_old/blob/6b7e2e1bdbd50299cee4075ff48d7323c05758bc/src/duckling/time/pred.clj#L333