Re: questions on libraries, pattern matching etc

[Duncan Mak <duncanmak@gmail.com>]

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

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


Duncan.

On Sun, Dec 15, 2019 at 7:59 PM Per Bothner <per@bothner.com> wrote:

> On 12/15/19 3:46 PM, Ben wrote:
> > hi
> > I'd like to test how I can use pattern match in Kawa. First I did try to
> use Kawas pattern matching function, but from what I saw it is a bit
> limited, for example there is no matching of lists.
>
> Actually, there is matching of lists, but by matching them as general
> sequences:
>
> #|kawa:1|# (! [a b c @rest] [1 2 3 4 5 6])
> #|kawa:2|# (format "a: ~a b: ~a c: ~a rest: ~a~%" a b c rest)
> a: 1 b: 2 c: 3 rest: #(4 5 6)
>
> Implementing more general matching is mainly an issue of design including
> deciding on a syntax.
> Fundamentally, should be syntax for matching a pair be:
>
> (! (pat_car . pat_cdr) value)
>
> or:
>
> (! (cons pat_car pat_cdr) value)
>
> or something else?
> The latter is used in Racket, and is more flexible, I believe, but not as
> elegant -
> which ties back to fundamental awkwardness with the Scheme evaluation
> model.
>
> Of course once we/I decide on a syntax, then it needs to be implemented,
> but
> should be fairly straight-forward, given the existing framework.
> --
>         --Per Bothner
> per@bothner.com   http://per.bothner.com/
>


-- 
Duncan.