Re: questions on libraries, pattern matching etc

[Per Bothner <per@bothner.com>]

On 6/29/20 1:50 PM, Duncan Mak wrote:
> Hello Per,
> 
> About the syntax for a match macro, work on SRFI 200 (draft) just started:
> 
> https://srfi.schemers.org/srfi-200/srfi-200.html

I haven't read it in detail, but it looks like the proposed pattern syntax
is more-or-less compatible with Kawa.

(There are lots of SRFIs coming out, and I've given up trying to pay close
attention, especially since may of them are philosophically incompatible
with Kawa.  For example, Kawa has a consistent and powerful "sequence"
concept and I think it's a mistake to define a large library of procedures
for every sequence type, as seems to be the direction of R7RS-large.)

The key thing about patterns in Kawa is they are integrated in the
standard syntax forms, rather than being a pure "add-on" library feature.
For example, the "variable" defined in a LET form can be a pattern.

Also, not that in Kawa patterns and type-specifiers are integrated:  a PATTERN
can be:
   PATTERN ::TYPE

To extend the syntax of Kawa patterns (which is highly deirable,
and could plausible be done in the style of SRFI-200) one would need
to extend kawa/lang/BindDecls.java, primarily.
Not completely trivial, but not impossible either :-)

> What do you think about adopting the syntax for the Wright-Cartwright-Shinn matcher?
> 
> I've been trying to use match.scm (and its variants) in Kawa and simple patterns kinda work, but I see that:
> 
> - matching records
> - matching quasiquotes
> 
> These two parts don't seem to be working.
> 
> For now, I've backed out of using match.scm due to the missing features, but it'd really be nice to have a match macro that comes with Kawa scheme, following one of the grammar listed in the SRFI.
> 
> Going a different direction, this design for a CASE* macro is also interesting, https://github.com/axch/pattern-case/blob/master/pattern-matching.txt

While I'm OK with adding verious SRFI libraries for cmpatibility, patterns in
the core part of Kawa should follow (and extend) the design in:
https://www.gnu.org/software/kawa/Variables-and-Patterns.html#meta-pattern
https://www.gnu.org/software/kawa/Definitions.html
https://www.gnu.org/software/kawa/Local-binding-constructs.html
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/