Re: Improving Emacs' iCalendar support

[Richard Lawrence <rwl@recursewithless.net>]

Dear emacs-devel,

Richard Lawrence <rwl@recursewithless.net> writes:

> I would like to start a discussion about improving Emacs' iCalendar
> support, beyond what is already available in icalendar.el. I personally
> would like to see Emacs gain a more full-fledged RFC5545 implementation
> that is primarily designed as a library for other applications to use.

Time for an update about this: I've been working steadily on the parser,
and I reached an important milestone this week: the parser can now parse
and reproduce all the examples in RFC5545, as well as my own calendar
data! There is still a lot of work to do, but this seems like a good
moment to ask again for feedback from anyone who's interested.

The repository where I've been doing this work is here:
https://sr.ht/~wyleyr/icalendar-el/

There are some instructions in the README for how to get started playing
around with the parser, for those interested in trying it out.

Based on the feedback I got earlier, I've made a few important design
decisions at this stage:

1) The basic form of the syntax tree is based on the format of the Org
parse tree in org-element-ast.el (though for now I have not implemented
any of the performance optimizations). Syntax nodes are a four-element
list of a type symbol, a metadata structure, a value, and a list of
children. Type symbols are used to store metadata about all the
iCalendar grammar categories and to do type-based dispatch in the
parser.

2) As far as possible, I have represented iCalendar data using "native"
data types in Emacs: dates are represented as calendar.el dates,
date-times as decoded-times, text as strings or buffer regions, etc.
This should hopefully make it as easy as possible to use iCalendar data
and parse trees from elsewhere in Emacs. In cases where no data type
already exists, the data types I defined are usually simple lists with
accessors defined for different fields.

(My initial attempts used cl-structs for the data types, following Adam
Porter's suggestion, but I quickly found myself writing tons of
boilerplate to convert between these structs and the "native" formats,
so I abandoned it. I am using a struct for syntactic metadata stored by
the parser, though.)

3) I have focused a lot on making good documentation, since I think
Emacs' documentation system is one of its best features, and the lack of
documentation in icalendar.el is one of the things that makes it
difficult to work with. All the symbols in the library should have good
documentation available via M-x describe-symbol -- please let me know if
you find anything confusing or broken in these docs.

Many thanks in advance for your thoughts!

Best,
Richard