pcase defuns

[Andrew Hyatt]

Hi all,

As a part of a personal project, I wrote a way to define functions 
in an equivalent way to pcases.  For example:

(pcase-defun mytest (a b _)
 "Match on 'a 'b with the third argument a wildcard"
 "a b match")

(pcase-defun mytest (c ,var _)
 "Match on 'c binding VAR, with the third argument a wildcard"
 (format "c %s match" var) )

(mytest 'a 'b 'c) -> "a b match"
(mytest 'c 100 'c) -> "c 100 match"

This is all accomplished by a few small but tricky macros and a 
hashtable that holds all the rules.

I find this method of programming quite useful for certain kinds 
of problems, and pcase is close to what I want, but using pcase 
forced me to encapsulate all of my pattern matching logic in one 
function. Being able to have it spread out in pattern matching 
functions seems much nicer to me.

If this is of interest, I can either add this to the pcase module 
itself, create a package in gnu elpa, or (if there's some reason 
that it shouldn't be done) just keep it in a personal repository.

I'll wait for some guidance before creating a final version, with 
tests, wherever it should go.