GNU bug report logs - #58727
29.0.50; rx doc: Semantics of RX...

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Subject: bug#58727: closed (Re: 29.0.50; rx doc: Semantics of RX...)
Date: Tue, 25 Oct 2022 02:50:02 +0000

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Your bug report

#58727: 29.0.50; rx doc: Semantics of RX...

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 58727 <at> debbugs.gnu.org.

-- 
58727: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=58727
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: 58727-done <at> debbugs.gnu.org
Subject: Re: 29.0.50; rx doc: Semantics of RX...
Date: Tue, 25 Oct 2022 04:49:20 +0200

Mattias Engdegård <mattias.engdegard <at> gmail.com> writes:

> > A sentence like "rx forms are defined by their semantics" would help
> > to make that clear I think.
>
> Well, I added a phrase to that effect as well.

Thanks - I hope it was not too much.

> Thank you for your comments and suggestions!

And thank you for the implementation of these!


Regards,

Michael.

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From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.0.50; rx doc: Semantics of RX...
Date: Sun, 23 Oct 2022 04:32:17 +0200

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.

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