User guide

The guide explains each part of the library in depth. It is organised from the foundational concept (the Rata Die day count) outward to the individual calendars and the supporting tools.

• Rata Die — the conversion pivot
• Calendars and conversion
• Parsing dates
• Formatting dates
• Hebrew numerals (gematria)
• Month and weekday names
• Hebrew calendar internals
• The Anno Mundi era and the “missing years”
• Astronomy and locations
• Holidays
• Religious times
• Alternative calendars
• Command-line interface

How the pieces fit together

The one rule

A calendar date converts to an integer Rata Die (RD) and rebuilds from one (to_rd / from_rd). Conversion between any two calendars always routes through RD, so adding a new calendar never touches existing ones.

• Rata Die — the conversion pivot — the day-count pivot, the Weekday enum and convert().

• Calendars and conversion — the Gregorian, Julian and Hebrew date types and the reform helper.

• Parsing dates and Formatting dates — reading and rendering dates.

• Hebrew numerals (gematria) — integers ↔ Hebrew numerals.

• Month and weekday names — month and weekday name tables.

• Hebrew calendar internals — the molad, dechiyot, year typing, keviah and Metonic cycle.

• The Anno Mundi era and the “missing years” — the era count and the “missing years”.