From: Michael Heerdegen <michael_heerdegen@web.de>
To: 58727@debbugs.gnu.org
Subject: bug#58727: 29.0.50; rx doc: Semantics of RX...
Date: Sun, 23 Oct 2022 04:32:17 +0200 [thread overview]
Message-ID: <87tu3v2rta.fsf@web.de> (raw)
Hello,
please document the semantics of multiple RXs for the RX repetition
operators (and maybe grouping operators, too).
The resulting regexps are concatenating like with an implicit `seq'.
This is not trivial, though: in stringish regexps the repetition
operators are only unary, and different interpretations would make sense
for `rx' (implicit `seq', implicit `or').
The docstring of `rx' doesn't tell anything about this. The manual has
sentences like
| ‘(zero-or-more RX...)’
| ‘(0+ RX...)’
| Match the RXs zero or more times. Greedy by default.
| Corresponding string regexp: ‘A*’ (greedy), ‘A*?’ (non-greedy)
but that suffers from the same problem that the semantics of A are not
clear: A == (seq RX...) ?
Oh, and maybe let's also make more clear that `rx' always cares about
implicit grouping when necessary. For example, in
(info "(elisp) Rx Constructs") it's not trivial that e.g. in
‘(seq RX...)’
‘(sequence RX...)’
‘(: RX...)’
‘(and RX...)’
Match the RXs in sequence. Without arguments, the expression
matches the empty string.
Corresponding string regexp: ‘AB...’ (subexpressions in sequence).
`rx' silently adds shy grouping to the result, and the corresponding string
regexp in this case is more precisely \(?:AB...\). I think it is enough
to mention this implicit grouping feature once, but it is important to
spell it out.
TIA,
Michael.
next reply other threads:[~2022-10-23 2:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-23 2:32 Michael Heerdegen [this message]
2022-10-23 16:14 ` bug#58727: 29.0.50; rx doc: Semantics of RX Mattias Engdegård
2022-10-24 2:34 ` Michael Heerdegen
2022-10-24 12:49 ` Mattias Engdegård
2022-10-25 2:49 ` Michael Heerdegen
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