Both keep the same Typikon and read it a little differently, and until now
this library silently picked one reading and called it the Typikon. Two
differences are modelled, each one visible in the output and named in the
day's reason:
- The Protection of the Theotokos is a great feast in Slavic usage. Greek
practice ranks it lower, and the Church of Greece keeps it on 28 October
besides. This has teeth: rank is what lifts a Wednesday or Friday fast.
- Greek practice admits fish on any day of the Nativity Fast but Wednesday
and Friday until 17 December; Slavic practice keeps fish to Saturdays and
Sundays throughout.
Every jurisdiction carries the usage its books follow, and --tradition
overrides it for a parish that does not match its jurisdiction's default. The
difference in the calendar lives in a data overlay compiled in beside the
common menologion, which is where a local church's own commemorations would
go; the difference in the fast lives in the rule, because that is where it is.
Each rank also now carries the mark the books print beside it, circled cross,
cross and Jerusalem cross for great, vigil and polyeleos. Unicode has no glyph
for the polyeleos sign, a cross over a half-circle, so the Jerusalem cross
stands in as digital calendars generally settle on.
Python was never the house language here: the mw-* desktop surface it came
from is 39 bash scripts and was exactly one Python script, the one this was
extracted from. What it cost was distribution, a widget dependency that
needed pipx and a Python floor, and 24ms of interpreter startup before a line
of the program ran.
The port is verified rather than asserted. Both implementations were run over
199,446 day-records, 26 jurisdictions across 21 years, with every field of
every record required to match; the JSON, the iCalendar and 480 renderings of
the text output are identical too. examples/dump.rs is the harness.
What the type system actually buys, which is less than the usual claim and
more than nothing:
- Level is an ordered enum, strictest first, so reads as 'a is
stricter' and relaxed_to() is the one place a feast can lift a fast. No
rule can get the direction backwards.
- Date is a newtype over the Julian Day Number and JulianDate is a separate
type, so a civil date and an ecclesiastical one cannot be mixed up. That
confusion is the single most common way calendar code goes wrong.
- Octets is a newtype in the iCalendar folder, because the bug it replaced
counted characters against a limit RFC 5545 states in octets.
- Movables is a struct, not a map, so a mistyped key is a compile error
rather than a None at the far end of the program.
Of the six defects an adversarial review found in the Python, exactly one had
a shape a type system would have caught. The rest were logic, and the tests
came with them.
The menologion is compiled in with include_str!, so the binary answers on its
own: 930KB, no runtime, 1.2ms to start against Python's 36ms.
funkpower