Re: [calsify] SKIP was Re: AD review of draft-ietf-calext-rscale-03

[Ken Murchison <[e-mail]>]

On 02/03/2015 10:08 AM, Cyrus Daboo wrote:
> Hi Ken,
>
> --On February 3, 2015 at 10:02:01 AM -0500 Ken Murchison 
> <[e-mail]> wrote:
>
>> It appears your previous rules properly handle the 30 Adar I (leap year)
>> case, but the new rules do not.  Can we come up with rules that can 
>> model
>> the 3 cases listed above?
>
> OK thanks for looking into that. If we want to provide full 
> flexibility to control what happens we would need to have two "skip" 
> indicators, one for skipping invalid months and one for skipping 
> invalid days (with the month one applied first, followed by the day 
> one). So:
>
> RRULE:FREQ=YEARLY;SKIP-MONTH=FORWARD;SKIP-DAY=FORWARD
>
> Would match the Hebrew birthday case you found.
>
> RRULE:FREQ=YEARLY;SKIP-MONTH=FORWARD;SKIP-DAY=BACKWARD
>
> Would match the behavior from my last email. If we find there really 
> is never a use case for the above, then we could stick with the single 
> SKIP option. But lets see if we can get a confirmation on that.
>

Cyrus,

I believe we can get by with just a single SKIP and your previous rules 
to handle both cases above (using Hebrew leap month):

RRULE:FREQ=YEARLY;RSCALE=HEBREW;SKIP=FORWARD;BYMONTH=5L;BYMONTHDAY=30

Would yield 1 Nisan (skipping forward both a month and day)


RRULE:FREQ=YEARLY;RSCALE=HEBREW;SKIP=FORWARD;BYMONTH=5L;BYMONTHDAY=-1

Would yield 29 Adar (skipping forward just a month)


For the BACKWARD cases, both BYMONTHDAY=30 and BYMONTHDAY=-1 would yield 
Shevat 30.


-- 
Kenneth Murchison
Principal Systems Software Engineer
Carnegie Mellon University