Re: modern regexes in emacs

["Mattias Engdegård" <mattiase@acm.org>]

26 feb. 2019 kl. 15.33 skrev Andreas Schwab <schwab@suse.de>:
> 
> If you want to byte-compile a form that contains a regexp object, a
> proper read syntax is required.
> 
> The object types without read syntax are rather ephemeral, unlikely to
> occur in byte-compiled forms.

Thanks for pointing that out. I'm not sure how it would work -- please bear with me.

Suppose we want to write (looking-at (pcre "a(b|c)")).
Then `pcre' is a macro returning a mutable object with the regexp in some canonical form -- a traditional Emacs regexp, perhaps, or normalised rx or something else. The object also has space for the internal compiled pattern, roughly struct re_pattern_buffer today.

As Richard pointed out, it is polite to make the object human-readable (for debugging, if nothing else). This means that we are either satisfied with the readability of the canonical form, or the original pattern is included around for this purpose.

Then (pcre "a(b|c)") might produce #s(regexp "a\\(b\\|c\\)" nil), which can be serialised and read, even by humans.
After its first use, the last slot would have become something like #<compiled-regexp 0xabc123>, but that would not occur in byte-compiled elisp code.