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* New rx implementation with extension constructs
@ 2019-09-02 21:19 Mattias Engdegård
  2019-09-04 14:18 ` Mattias Engdegård
  2019-09-06 14:09 ` Mattias Engdegård
  0 siblings, 2 replies; 13+ messages in thread
From: Mattias Engdegård @ 2019-09-02 21:19 UTC (permalink / raw)
  To: emacs-devel

The rx regexp notation is nice to use but the implementation isn't wonderful; there is a proposed replacement rewritten from the ground up. It is cleaner, has fewer bugs, and is maybe twice as fast.

Most importantly, there is now a proper extension mechanism: for global definitions,

 (rx-define snobol-identifier (seq alpha (0+ alnum))

which are available anywhere, and local ones,

 (rx-let ((natnum (1+ digit))
          (integer (seq (opt "-") natnum)))
   ...body...)

where a set of definitions are only available in a lexical scope. This zero-cost construct can be placed inside a function, or at top-level enclosing multiple variable and function definitions, all sharing the same named rx forms.

Both rx-define and rx-let admit two kinds of definitions:

 NAME RX-FORM
 NAME (ARGS...) RX-FORM

for plain rx symbols and for parametrised forms, respectively. For example:

 (rx-let ((name (1+ letter))
          (comma-separated (x) (seq x (0+ "," x))))
  (rx (comma-separated name)))

works just as expected. &rest arguments are permitted, and expand to implicit (seq ...) forms.
No provision was made for macros able to execute arbitrary Lisp code; I just couldn't find a use for them, and decided to wait until someone would tell me otherwise. Thus, all parametrised forms work by plain substitution.

The code currently resides at https://gitlab.com/mattiase/ry; it will naturally be renamed to `rx' once it's in the Emacs tree. It can be integrated in a separate branch of the Emacs source repo if you wish, or as patches if you prefer that for reviewing. The diffs don't make much sense since it is a reimplementation with very little in common with the old code.

The exact form of the extension mechanism isn't set in stone, and I'd welcome any suggestions for improvement.




^ permalink raw reply	[flat|nested] 13+ messages in thread

end of thread, other threads:[~2019-09-17 12:53 UTC | newest]

Thread overview: 13+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2019-09-02 21:19 New rx implementation with extension constructs Mattias Engdegård
2019-09-04 14:18 ` Mattias Engdegård
2019-09-04 17:03   ` Paul Eggert
2019-09-05 10:56     ` Aurélien Aptel
2019-09-05 11:17       ` Mattias Engdegård
2019-09-05 12:34         ` immerrr again
2019-09-05 19:04           ` Mattias Engdegård
2019-09-05 15:38   ` Noam Postavsky
2019-09-05 16:49     ` Mattias Engdegård
2019-09-06 14:09 ` Mattias Engdegård
2019-09-07 14:13   ` Noam Postavsky
     [not found]     ` <0E5A5E92-E48F-4003-A742-508663BA984A@acm.org>
2019-09-11 18:11       ` Mattias Engdegård
2019-09-17 12:53         ` Mattias Engdegård

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