From: "Mattias Engdegård" <mattiase@acm.org>
To: Michael Heerdegen <michael_heerdegen@web.de>
Cc: 50136@debbugs.gnu.org, monnier@iro.umontreal.ca
Subject: bug#50136: 28.0.50; A problem with rx-let expansion
Date: Fri, 20 Aug 2021 20:45:41 +0200 [thread overview]
Message-ID: <B4B50ED2-0692-48DF-82A4-977D44C6C3B0@acm.org> (raw)
In-Reply-To: <87y28whw1b.fsf@web.de>
20 aug. 2021 kl. 19.21 skrev Michael Heerdegen <michael_heerdegen@web.de>:
> I guess it's not very useful for the current mechanism. With a
> macro-like thing, the expansion would just not use the value if it's nil. The
> expander would check whether the argument was provided.
Yes. It was (and is) a trade-off between the simpler "template-like" semantics currently used and the programmatic "execute code" semantics of Lisp macros. The idea was that the simpler semantics would be simpler and sufficient for most uses, and `eval` forms could always be employed in other cases.
I'm still fretting over having made the wrong call, and that at least I should have omitted parametrised rx definitions until better understood.
If you just have one optional argument, try &rest -- at least its default-case semantics are crystal clear (no arguments inserted). Obviously, you could also use separate rx macros for different parameter lists:
(rx-let ((delimited (grp delim) (seq delim (group-n grp (* (not delim)) delim)))
(double-quoted (grp) (delimited grp ?\")))
etc.
next prev parent reply other threads:[~2021-08-20 18:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-20 13:59 bug#50136: 28.0.50; A problem with rx-let expansion Michael Heerdegen
2021-08-20 14:50 ` Michael Heerdegen
2021-08-20 15:23 ` Mattias Engdegård
2021-08-20 17:21 ` Michael Heerdegen
2021-08-20 18:45 ` Mattias Engdegård [this message]
2021-08-21 11:45 ` Michael Heerdegen
2021-08-21 13:02 ` Mattias Engdegård
2021-08-23 10:45 ` Michael Heerdegen
2021-08-23 12:38 ` Mattias Engdegård
2021-08-23 15:20 ` Mattias Engdegård
2021-08-23 16:59 ` Michael Heerdegen
2021-08-23 18:05 ` Mattias Engdegård
2021-08-21 3:21 ` Richard Stallman
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