Documentation:
<http://dpk.io/temp/extensible-match/README>

Implementation:
<https://gitlab.com/dpk/presrfis/-/tree/extensible-match/extensible-match>

As of writing (commit f6f13fe8), the implementation supports all documented features. However, it currently only runs in the (Chez Scheme) REPL and still hasn’t been sorted out into libraries with respect for phasing, etc.

Before making this a full SRFI and giving it consideration for the R7RS Large Batteries, this is approximately the to-do list:

- Gather feedback on the design at the pre-SRFI stage (hence this email ;-) )
- Add support for unordered patterns so it’s possible to match things like sets, hash tables, etc.
- Probably change away from syntax-case style fenders to providing an escape procedure to jump to the next matching clause. This would allow the code part of each match clause to be a full Scheme body rather than a single expression
- Improve the implementation of sequence matching to be based on a fast iterator protocol instead of bare lists, to make matching non-list sequencing types more efficient by not requiring them to be converted into a list first — possibly do this in conjunction with the next item (second design principle)
- Change the core of the implementation from consing up a list of matched variable values to using a mix of local variable bindings and multiple-value return to store matched variable values, to use efficient stack/register storage as much as possible and the heap as little as possible (second design principle)

Daphne