Calculate the date of Easter Sunday or Good Friday:

https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt

--
:wq
Mike Sanders

On Sat, 24 Feb 2024 21:15:56 -0000 (UTC), Mike Sanders wrote:

> Calculate the date of Easter Sunday or Good Friday:

Did you know that one of the requirements of the rules was that Easter
would never coincide with Passover? Because the sight of Christians
celebrating together with Jews was seen as heretical or something ...

On 24.02.2024 23:54, Lawrence D'Oliveiro wrote:
> On Sat, 24 Feb 2024 21:15:56 -0000 (UTC), Mike Sanders wrote:
>
>> Calculate the date of Easter Sunday or Good Friday:
>
> Did you know that one of the requirements of the rules was that Easter
> would never coincide with Passover? Because the sight of Christians
> celebrating together with Jews was seen as heretical or something ...

.... and that there's not a unique definition of Easter.

Janis

On Sat, 24 Feb 2024 23:57:16 +0100, Janis Papanagnou wrote:

> ... and that there's not a unique definition of Easter.

Easter, Christmas ... both ancient pagan festivals co-opted by the
Christians and given an invented meaning under their ideology, for their
own propaganda purposes.

Just like they took a lot of existing pagan deities (e.g. in Celtic lands)
and reinvented them as “saints”.

On 25.02.2024 00:02, Lawrence D'Oliveiro wrote:
> On Sat, 24 Feb 2024 23:57:16 +0100, Janis Papanagnou wrote:
>
>> ... and that there's not a unique definition of Easter.
>
> Easter, Christmas ... both ancient pagan festivals co-opted by the
> Christians and given an invented meaning under their ideology, for their
> own propaganda purposes.

Yes, the associated rites were of pagan origin. The dates of Easter -
the topic here - still not unique. There's different calculations for
different christian churches; the catholics calculate it differently
from the orthodox christians, still today. - So Easter is peobably
not a good choice for a C program calculation if not parameterized or
explicitly documented to be restricted to only one specific religious
culture.

Janis

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

> Did you know that one of the requirements of the rules was that Easter
> would never coincide with Passover? Because the sight of Christians
> celebrating together with Jews was seen as heretical or something ...

Oh yeah, lots of horror stories committed by & against the 'us & them'.
Isn't a culture on the planet, so far as I can see, that has not been
both prey & predacious. I want to say something like 'that's life',
but its not a very satisfying reply...

--
:wq
Mike Sanders

Lawrence D'Oliveiro <ldo@nz.invalid> writes:
> On Sat, 24 Feb 2024 23:57:16 +0100, Janis Papanagnou wrote:
>> ... and that there's not a unique definition of Easter.
>
> Easter, Christmas ... both ancient pagan festivals co-opted by the
> Christians and given an invented meaning under their ideology, for their
> own propaganda purposes.
>
> Just like they took a lot of existing pagan deities (e.g. in Celtic lands)
> and reinvented them as “saints”.

Yes, please, this newsgroup really needs a religious debate!

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Medtronic
void Void(void) { Void(); } /* The recursive call of the void */

On 2024-02-25, Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
> On 25.02.2024 00:02, Lawrence D'Oliveiro wrote:
>> On Sat, 24 Feb 2024 23:57:16 +0100, Janis Papanagnou wrote:
>>
>>> ... and that there's not a unique definition of Easter.
>>
>> Easter, Christmas ... both ancient pagan festivals co-opted by the
>> Christians and given an invented meaning under their ideology, for their
>> own propaganda purposes.
>
> Yes, the associated rites were of pagan origin.

Pretty much all Christian celebrations are hijacks of pagan ones.

--
TXR Programming Language: http://nongnu.org/txr
Cygnal: Cygwin Native Application Library: http://kylheku.com/cygnal
Mastodon: @Kazinator@mstdn.ca

On Sun, 25 Feb 2024 01:33:35 -0000 (UTC), Mike Sanders wrote:

> Oh yeah, lots of horror stories committed by & against the 'us & them'.
> Isn't a culture on the planet, so far as I can see, that has not been
> both prey & predacious. I want to say something like 'that's life', but
> its not a very satisfying reply...

You know how most of these religions have, as one of their core
principles, that “our god is the only true god, all other gods are false”?

If they would all agree to get rid of that, it would be a good step on the
road to religious tolerance.

On Sun, 25 Feb 2024 02:00:43 +0100, Janis Papanagnou wrote:

> On 25.02.2024 00:02, Lawrence D'Oliveiro wrote:
>> On Sat, 24 Feb 2024 23:57:16 +0100, Janis Papanagnou wrote:
>>
>>> ... and that there's not a unique definition of Easter.
>>
>> Easter, Christmas ... both ancient pagan festivals co-opted by the
>> Christians and given an invented meaning under their ideology, for their
>> own propaganda purposes.
>
> Yes, the associated rites were of pagan origin. The dates of Easter -
> the topic here - still not unique. There's different calculations for
> different christian churches; the catholics calculate it differently
> from the orthodox christians, still today.

As some countries recognize Good Friday and/or Easter Sunday as
statutory holidays, and have /legal/ definitions for those dates.

For instance, the Government of Canada defines Easter Sunday as
"the first Sunday after the first full moon in spring (after March 21st)".
(I don't know if this coincides with /any/ religious definition or not.)

> So Easter is peobably
> not a good choice for a C program calculation if not parameterized or
> explicitly documented to be restricted to only one specific religious
> culture.

--
Lew Pitcher
"In Skills We Trust"

On Sat, 24 Feb 2024 21:15:56 +0000, Mike Sanders wrote:

> Calculate the date of Easter Sunday or Good Friday:
>
> https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt

I don't have the expertise to discuss whether or not your code
properly implements the calculations necessary to determine the
date of Good Friday and/or Easter. However, I /do/ have some
expertise on writing understandable code.

My suggestions, with respect to your program, would be to
a) name your objects with relevant, understandable names
You code uses quite a lot of meaningless one-letter
objects, and it is difficult to keep track of the
purpose of the calculations using them.
b) Don't place your calculations /in/ the object initializations.
Doing so obfuscates the intent of the logic, and makes
problem determination and resolution difficult.

Otherwise, it /appears/ to do the job. Good first attempt.
--
Lew Pitcher
"In Skills We Trust"

On 25.02.2024 17:58, Lew Pitcher wrote:
> On Sun, 25 Feb 2024 02:00:43 +0100, Janis Papanagnou wrote:
>>
>> [...] There's different calculations for
>> different christian churches; the catholics calculate it differently
>> from the orthodox christians, still today.
>
> As some countries recognize Good Friday and/or Easter Sunday as
> statutory holidays, and have /legal/ definitions for those dates.
>
> For instance, the Government of Canada defines Easter Sunday as
> "the first Sunday after the first full moon in spring (after March 21st)".
> (I don't know if this coincides with /any/ religious definition or not.)

In Germany it's also legally defined. But it's difficult.

First, most holidays (but one) are defined not on the country level
but individually at states level, but there's still common holidays
across all states. This is not surprising since the states have
different predominant religious variants in their population, so the
"protestant countries" have not the same holidays as the "catholic
countries" (and the orthodox, for example, are not represented in
the legislation at all, e.g. when concerning Easter), and there are
also other state specific holidays. And even within a state there's
regional differences. There are also legislative special rules, e.g.
for Israeli holidays, that Germans have to respect, and that provide
more free time for people of this religious orientation.

Then there's a distinction of fixed and varying holidays. Easter is
from the latter, while Christmas from the former.

And, IIUC, the actual dates rely on a "Church Year", which differs
between catholics/protestants and orthodox christians.

I can't say whether the legislation is referring to some churches'
documents and/or definitions, but it's more likely they copied such
definitions into the legislative texts, since people must be able to
rely on legislative texts. But on a quick view into the Bavarian law
I could not find the Christian holidays listed by date; they are just
referred to by their name.

It's complex.

Janis

Lew Pitcher <lew.pitcher@digitalfreehold.ca> wrote:

> I don't have the expertise to discuss whether or not your code
> properly implements the calculations necessary to determine the
> date of Good Friday and/or Easter. However, I /do/ have some
> expertise on writing understandable code.

One thing while I'm thinking about it: allot of discussion up-thread
failed to note that officially mandated Easter dating is really
based a Lunar date mapped onto the Gregorian calendar. Yet another
layer of abstraction.
> My suggestions, with respect to your program, would be to
> a) name your objects with relevant, understandable names
> You code uses quite a lot of meaningless one-letter
> objects, and it is difficult to keep track of the
> purpose of the calculations using them.
> b) Don't place your calculations /in/ the object initializations.
> Doing so obfuscates the intent of the logic, and makes
> problem determination and resolution difficult.
>
> Otherwise, it /appears/ to do the job. Good first attempt.

Thanks Lew appreciate the helpful comments, still a newbie,
I move forward if ever so slowly.

--
:wq
Mike Sanders

On 26.02.2024 04:12, Mike Sanders wrote:
>
> One thing while I'm thinking about it: allot of discussion up-thread
> failed to note that officially mandated Easter dating is really
> based a Lunar date mapped onto the Gregorian calendar. [...]

Not sure which instance of "official" you are referring to; there's
just no "official" mandate unless you are restricting yourself to a
global authority instance (which does not exist) or not considering
that any single instance cannot define a "general" rule that would
be valid worldwide. Face it; Easter dates just differ on this planet!

The "western" churches switched to Gregorian calendar while the
"eastern" churches stayed with the Julian _to calculate the Easter
date_. (Both based on lunar constellation, but that's irrelevant.)

I suggest to leave your country, visit (for example) Greece, and ask
the people there what they think about your definition. Or take the
simple approach; inspect Wikipedia or other established encyclopedias.

And both dates, western and eastern, are anyway arbitrary. But if you
decide to neglect the existing facts, either by wrongly assuming that
there's only one "correct" Easter date, or by (arrogantly?) presuming
that one is more correct than the other, then you are discriminating
Christian folks that follow the one [arbitrary] definition (or the
other).

Janis

PS: Just to prevent you from a fallacy; for the date calculation of
Easter it's irrelevant whether "we" have "now" switched to Gregorian
calendar [mostly]. (Think about it before you step into that pit.)

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
> On Sat, 24 Feb 2024 21:15:56 -0000 (UTC), Mike Sanders wrote:
>
>> Calculate the date of Easter Sunday or Good Friday:
>
> Did you know that one of the requirements of the rules was that Easter
> would never coincide with Passover? Because the sight of Christians
> celebrating together with Jews was seen as heretical or something ...

I have never heard of this one and I don't think it's true...

Easter is a day while passover last eight days and it happens that one of
those days is the easter sunday as in 2022 when passover started April 15 and
ester was April 17.

The calculation of easter is quite complex and use the "epact" and "golden
number" associated to the year, but the short answer "the first sunday after
the full moon after the spring equinox" usually gives the right answer.
Just remember that it is the "official spring equinox" March 21 and not the
"real" one that can happen on the 19,20(usually, like this year)
or 21 and the "official full moon" that can differ one or two days from the
"real".

For a full discussion see: <https://www.tondering.dk/claus/cal/easter.php>,
part of "The Calendar FAQ".

G

On 25/02/2024 18:39, Lew Pitcher wrote:
> On Sat, 24 Feb 2024 21:15:56 +0000, Mike Sanders wrote:
>
>> Calculate the date of Easter Sunday or Good Friday:
>>
>> https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt
>
> I don't have the expertise to discuss whether or not your code
> properly implements the calculations necessary to determine the
> date of Good Friday and/or Easter. However, I /do/ have some
> expertise on writing understandable code.
>
> My suggestions, with respect to your program, would be to
> a) name your objects with relevant, understandable names
> You code uses quite a lot of meaningless one-letter
> objects, and it is difficult to keep track of the
> purpose of the calculations using them.

I agree here.

I'd also avoid single-letter capital letter variables, and avoid
single-letter variables that are easily misread (so don't use "L" or
"O", big or small). Single-letter variables are fine if their scope is
small and their meaning is clear - such as "i" for a loop variable, and
"x" and "y" for coordinates.

Good names here, together with some comments, would go a long way to
making it possible to understand your algorithm here. Links to web
pages for reference are useful (and it's always polite to give your
references), but remember that web pages don't last for ever - try to
make your code stand alone as code, or at least have enough comments to
cover the information.

> b) Don't place your calculations /in/ the object initializations.
> Doing so obfuscates the intent of the logic, and makes
> problem determination and resolution difficult.

I'd disagree with that one. Initialise your variables when you have
something to put in them, and that is often a calculated value.

>
> Otherwise, it /appears/ to do the job. Good first attempt.

Some other suggestions:

Don't use "int" when you mean "bool". That applies to parameters,
return types, and variables.

Don't have one function that appears to do two different things. It's
much better to have "isEaster()" and "isGoodFriday()" functions.
Clearly these are heavily related, so have a static helper function that
does the common calculations.

Consider making and using several general functions, rather than having
a single impenetrable function. You might have a "numberOfDaysInYear()"
function, and functions for converting (day, month) pairs back and forth
to the number of days since the first of January. You can have lunar
calculations also based on the number of days from a given starting
point (perhaps using Unix epoch time rather than struct tm). Then you
can have a "findEaster()" function that returns the date of Easter for a
given year as the number of days from the first of January.

On 2024-02-25, Lew Pitcher wrote:
> On Sun, 25 Feb 2024 02:00:43 +0100, Janis Papanagnou wrote:
>> [...]
>> Yes, the associated rites were of pagan origin. The dates of Easter -
>> the topic here - still not unique. There's different calculations for
>> different christian churches; the catholics calculate it differently
>> from the orthodox christians, still today.
>
> As some countries recognize Good Friday and/or Easter Sunday as
> statutory holidays, and have /legal/ definitions for those dates.
>
> For instance, the Government of Canada defines Easter Sunday as
> "the first Sunday after the first full moon in spring (after March 21st)".
> (I don't know if this coincides with /any/ religious definition or not.)

Close enough to Catholic -- "First Sunday after the first full moon
after the Spring Equinox".

Equinox is on the 19th, first full moon is the 31st. Should line up (at
least this year).

--
|_|O|_|
|_|_|O| Github: https://github.com/dpurgert
|O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1 E067 6D65 70E5 4CE7 2860

David Brown <david.brown@hesbynett.no> writes:

> On 25/02/2024 18:39, Lew Pitcher wrote:
>> On Sat, 24 Feb 2024 21:15:56 +0000, Mike Sanders wrote:
>>
>>> Calculate the date of Easter Sunday or Good Friday:
>>>
>>> https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt
>> I don't have the expertise to discuss whether or not your code
>> properly implements the calculations necessary to determine the
>> date of Good Friday and/or Easter. However, I /do/ have some
>> expertise on writing understandable code.
>> My suggestions, with respect to your program, would be to
>> a) name your objects with relevant, understandable names
>> You code uses quite a lot of meaningless one-letter
>> objects, and it is difficult to keep track of the
>> purpose of the calculations using them.
>
> I agree here.

I challenge the "use better names" to try it. The trouble with this
sort of code is, I suspect, that the quantities don't correspond to
anything that can be clearly named. I may be wrong as I don't know this
form, but it true of the much better known Zeller's Congruence.

I think the correct way to present an algorithm like this if to include
a block comment than documents and explains the formula (using whatver
names are conventional), followed by code that uses the same names to do
the calculation.

> I'd also avoid single-letter capital letter variables, and avoid
> single-letter variables that are easily misread (so don't use "L" or "O",
> big or small). Single-letter variables are fine if their scope is small
> and their meaning is clear - such as "i" for a loop variable, and "x" and
> "y" for coordinates.

In this case, I would use the conventional names (if there are any) even
if this violates the usual programming conventions. All supposing that
the formula has been explained in a comment using exactly those names.

> Good names here, together with some comments, would go a long way to making
> it possible to understand your algorithm here.

Have you tried? It may well detract from the explanations in the
references. (I am hoping that the referenced URLs explain the formula.)

> Links to web pages for
> reference are useful (and it's always polite to give your references), but
> remember that web pages don't last for ever - try to make your code stand
> alone as code, or at least have enough comments to cover the information.
>
>> b) Don't place your calculations /in/ the object initializations.
>> Doing so obfuscates the intent of the logic, and makes
>> problem determination and resolution difficult.
>
> I'd disagree with that one. Initialise your variables when you have
> something to put in them, and that is often a calculated value.

Yes, and I'd make them all const to show that they just name quantities
to simplify later calculations. That would force the adjustments to the
day, month and year (to get good Friday) to be in another function. The
logical one would be a separate test function for that date (as you have
suggested):

> Don't have one function that appears to do two different things.

Yes. I was taught a phrase about function arguments: "pass data not
control".

> It's much
> better to have "isEaster()" and "isGoodFriday()" functions. Clearly these
> are heavily related, so have a static helper function that does the common
> calculations.

--
Ben.

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:

> Not sure which instance of "official" you are referring to; there's
> just no "official" mandate unless you are restricting yourself to a
> global authority instance (which does not exist) or not considering
> that any single instance cannot define a "general" rule that would
> be valid worldwide. Face it; Easter dates just differ on this planet!

The inference is the 'official' governance of a given municipality or
provence using the Gregorian calendar (updated the URL notes last night
to, I hope, clarify)...

> PS: Just to prevent you from a fallacy; for the date calculation of
> Easter it's irrelevant whether "we" have "now" switched to Gregorian
> calendar [mostly]. (Think about it before you step into that pit.)

Not me =) I'm not touching the Julian variant, heck I got lucky (and
spent way too much time) with the one I cobbled together as it is.

So tell me, what are you coding these days? Haven't seen much from you
lately...

--
:wq
Mike Sanders

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:

> And both dates, western and eastern, are anyway arbitrary. But if you
> decide to neglect the existing facts, either by wrongly assuming that
> there's only one "correct" Easter date, or by (arrogantly?) presuming
> that one is more correct than the other, then you are discriminating
> Christian folks that follow the one [arbitrary] definition (or the
> other).

And what's this? c'mon now, there's nothing arrogant or presumptuous here.
I'm not discriminating against anyone (I'm Catholic if it makes a difference).
Now then - don't start an argument where there is none...

--
:wq
Mike Sanders

David Brown <david.brown@hesbynett.no> wrote:

> Don't use "int" when you mean "bool". That applies to parameters,
> return types, and variables.

But I dont mean bool, I mean int, because the function (well my
private code at any rate) now includes other Holi/Holy days:

int foo(const struct tm *now, int hDay);

switch (hDay)...

But you all still raise some good points.

--
:wq
Mike Sanders

On 26/02/2024 14:04, Ben Bacarisse wrote:
> David Brown <david.brown@hesbynett.no> writes:
>
>> On 25/02/2024 18:39, Lew Pitcher wrote:
>>> On Sat, 24 Feb 2024 21:15:56 +0000, Mike Sanders wrote:
>>>
>>>> Calculate the date of Easter Sunday or Good Friday:
>>>>
>>>> https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt
>>> I don't have the expertise to discuss whether or not your code
>>> properly implements the calculations necessary to determine the
>>> date of Good Friday and/or Easter. However, I /do/ have some
>>> expertise on writing understandable code.
>>> My suggestions, with respect to your program, would be to
>>> a) name your objects with relevant, understandable names
>>> You code uses quite a lot of meaningless one-letter
>>> objects, and it is difficult to keep track of the
>>> purpose of the calculations using them.
>>
>> I agree here.
>
> I challenge the "use better names" to try it. The trouble with this
> sort of code is, I suspect, that the quantities don't correspond to
> anything that can be clearly named. I may be wrong as I don't know this
> form, but it true of the much better known Zeller's Congruence.

Yes, I realise that's likely to be a problem here. For variables that
exist solely to break up a long complicated calculation into manageable
parts, good names are hard or impossible.

However, I would guess - without having looked at the details of the
algorithm - that this could be split into parts that are a bit clearer,
and at least some of the variables could then have names showing what's
going on. You might have the offset into the lunar month, or the number
of days in February, or a boolean for before/after the spring equinox.

If the expressions can only be split in somewhat arbitrary positions,
and therefore the variables have arbitrary and meaningless names, so be
it. But if it is possible and practical to do better, then I'd
recommend that.

>
> I think the correct way to present an algorithm like this if to include
> a block comment than documents and explains the formula (using whatver
> names are conventional), followed by code that uses the same names to do
> the calculation.

That is something I also suggested (without the detail of the names).

>
>> I'd also avoid single-letter capital letter variables, and avoid
>> single-letter variables that are easily misread (so don't use "L" or "O",
>> big or small). Single-letter variables are fine if their scope is small
>> and their meaning is clear - such as "i" for a loop variable, and "x" and
>> "y" for coordinates.
>
> In this case, I would use the conventional names (if there are any) even
> if this violates the usual programming conventions. All supposing that
> the formula has been explained in a comment using exactly those names.
>

Agreed. Clear and understandable code is more important than
conventions. (But names like "l" or "O" are rarely clear, even if they
are used in the context of the documentation of an algorithm.)

>> Good names here, together with some comments, would go a long way to making
>> it possible to understand your algorithm here.
>
> Have you tried? It may well detract from the explanations in the
> references. (I am hoping that the referenced URLs explain the formula.)
>
>> Links to web pages for
>> reference are useful (and it's always polite to give your references), but
>> remember that web pages don't last for ever - try to make your code stand
>> alone as code, or at least have enough comments to cover the information.
>>
>>> b) Don't place your calculations /in/ the object initializations.
>>> Doing so obfuscates the intent of the logic, and makes
>>> problem determination and resolution difficult.
>>
>> I'd disagree with that one. Initialise your variables when you have
>> something to put in them, and that is often a calculated value.
>
> Yes, and I'd make them all const to show that they just name quantities
> to simplify later calculations. That would force the adjustments to the
> day, month and year (to get good Friday) to be in another function.

Agreed - I think it is often clearer to have const variables that are
set once and never changed, so that you can always see exactly what
value they have, and when it is set.

> The
> logical one would be a separate test function for that date (as you have
> suggested):
>
>> Don't have one function that appears to do two different things.
>
> Yes. I was taught a phrase about function arguments: "pass data not
> control".
>

That's a good way to put it.

>> It's much
>> better to have "isEaster()" and "isGoodFriday()" functions. Clearly these
>> are heavily related, so have a static helper function that does the common
>> calculations.
>

On 26.02.2024 11:45, David Brown wrote:
> On 25/02/2024 18:39, Lew Pitcher wrote:
>> On Sat, 24 Feb 2024 21:15:56 +0000, Mike Sanders wrote:
>>
>>> Calculate the date of Easter Sunday or Good Friday:
>>> https://busybox.neocities.org/notes/is-easter-or-goodfriday.txt
>>
>> [...]
>>
>> My suggestions, with respect to your program, would be to
>> a) name your objects with relevant, understandable names
>> You code uses quite a lot of meaningless one-letter
>> objects, and it is difficult to keep track of the
>> purpose of the calculations using them.
>
> [...]
>
> Good names here, together with some comments, would go a long way to
> making it possible to understand your algorithm here. Links to web
> pages for reference are useful (and it's always polite to give your
> references), but remember that web pages don't last for ever - try to
> make your code stand alone as code, or at least have enough comments to
> cover the information.

Yes. Often it is the case that some magic formula is just copied
from some place without knowledge. (I suspect here too.) At least
a reference of the source of the formula should be provided with
the code! (At first glance it seems to be the so called Spencer's
formula [1922], published by someone else already in 1876.[*])

Over the years there had been many formulas, variants, refinements
introducing correction factors, etc. In the Wikipedias you should
find enough information[**].

>
> Consider making and using several general functions, rather than having
> a single impenetrable function. You might have a "numberOfDaysInYear()"
> function, and functions for converting (day, month) pairs back and forth
> to the number of days since the first of January. You can have lunar
> calculations also based on the number of days from a given starting
> point (perhaps using Unix epoch time rather than struct tm). Then you
> can have a "findEaster()" function that returns the date of Easter for a
> given year as the number of days from the first of January.

I'd expect that formulating the algorithm/formula using FP numbers
could probably make it also a bit simpler. (But I haven't tried.)
If you consider the actual task you observe that you somehow have
to map the lunar period (~30 d) to the sun period (~365 d), where
these cycles are not exact (not integral) and they are numerically
not synchronous, plus the weekday mapping (actually a third cycle,
in the calculation, here of integral type). This whole set of scalar
integers seem to emulate these inherent issues as correction factors
and few of them will represent real world entities.

Janis

[*] https://de.wikipedia.org/wiki/Spencers_Osterformel

[**] I picked the links from the German Wikipedia - apologies for
that - but I think that articles like these should be available in
other languages as well if you search for the respective keywords.
Easter date (also listing the two prevalent Easter definitions):
https://de.wikipedia.org/wiki/Osterdatum
Easter computation (mentioning also the necessary corrections):
https://de.wikipedia.org/wiki/Computus_(Osterrechnung)
Gauss' formulas and historic:
https://de.wikipedia.org/wiki/Gau%C3%9Fsche_Osterformel
And a general article about Easter (for the cultural basics):
https://de.wikipedia.org/wiki/Ostern

On 26.02.2024 15:46, David Brown wrote:
>
> Yes, I realise that's likely to be a problem here. For variables that
> exist solely to break up a long complicated calculation into manageable
> parts, good names are hard or impossible.
>
> However, I would guess - without having looked at the details of the
> algorithm - that this could be split into parts that are a bit clearer,

Unfortunately not, I fear.

> and at least some of the variables could then have names showing what's
> going on. You might have the offset into the lunar month, or the number
> of days in February, or a boolean for before/after the spring equinox.

You seem to have chosen a source where "Spencer's" algorithm is
described. In a corresponding Wikipedia article (here in German:
e.g. https://de.wikipedia.org/wiki/Spencers_Osterformel)
you find the same non-descriptive names.

>
> If the expressions can only be split in somewhat arbitrary positions,
> and therefore the variables have arbitrary and meaningless names, so be
> it. But if it is possible and practical to do better, then I'd
> recommend that.

If you put in a reference to the document source - while not
explaining anything - that might suffice. Otherwise you'd have
to spend more effort describing the variables in detail.

Janis

On 26.02.2024 15:26, Mike Sanders wrote:
> Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:
>
>> Not sure which instance of "official" you are referring to; there's
>> just no "official" mandate unless you are restricting yourself to a
>> global authority instance (which does not exist) or not considering
>> that any single instance cannot define a "general" rule that would
>> be valid worldwide. Face it; Easter dates just differ on this planet!
>
> The inference is the 'official' governance of a given municipality or
> provence using the Gregorian calendar (updated the URL notes last night
> to, I hope, clarify)...

(Despite my note you stepped into the fallacy trap.)

One final try to help you here: Greece, like most other countries in
the world, uses the Gregorian calendar. The Greek orthodox church, as
just one example of eastern churches, has not changed the calculation
for Easter. That's not a mistake.

>
>> PS: Just to prevent you from a fallacy; for the date calculation of
>> Easter it's irrelevant whether "we" have "now" switched to Gregorian
>> calendar [mostly]. (Think about it before you step into that pit.)
>
> Not me =) I'm not touching the Julian variant, heck I got lucky (and
> spent way too much time) with the one I cobbled together as it is.

The Wikipedia sources I provided elsethread show both existing Easter
calculations that are in use world wide. So it's easy to reflect the
real world in your code in a non-discriminating way. But if you prefer
to ignore hundreds million orthodox Christians[*] that's of course
completely your decision.

Janis

[*]
https://de.wikipedia.org/wiki/Liste_der_L%C3%A4nder_nach_christlicher_Bev%C3%B6lkerung