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Postings from December 1999
Hi, I'm sending this again as I suspect that sending it from a
different to normal mail address yesterday might have made the list
drop me on the floor. Sorry for the noise if this isn't the case.
------- Forwarded Message
Date: Wed, 01 Dec 1999 17:04:01 +0000
Subject: Re: [ID 19991130.003] Assignment to List Breaks \G.
In-reply-to: Message from Ilya Zakharevich <ilya@math.ohio-state.edu> "of Tue, 30 Nov 1999 11:43:00 EST."
<199911301643.LAA12574@monk.mps.ohio-state.edu>
To: Ilya Zakharevich <ilya@math.ohio-state.edu>
Cc: rjk@linguist.dartmouth.edu (Ronald J Kimball), merlyn@stonehenge.com,
desar@front1m.grolier.fr, ralph@inputplus.demon.co.uk (Ralph Corderoy),
perl5-porters@perl.org
Message-id: <199912011704.RAA105502@cm01.ess>
Content-transfer-encoding: 7BIT
Ronald J Kimball writes:
> This is the expected behavior for m//g in a list context. The regular
> expression is applied repeatedly until it no longer matches, and the
> return value is a list of all the substrings matched. After the final
> application of the regex, which fails to match, pos() is reset to the
> beginning of the string.
Hi, thanks for all the replies. Having put -Dr to good use I fully
understand what is happening with my example script. However, I'd like
to put a case forward that this behaviour is broken and judging from
Randal's question in
http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/1999-10/msg01047.html
there might be others that agree.
Normally, the use of context in Perl to `do the right thing' works well.
I'd suggest that the overloading of /g based on context allows only two
alternatives (/g and no /g) to be selected from a larger desired set of
operations.
If I want to match many times, possibly leaving pos alone on failure,
then the existing /g and /c work well.
@w = /(\w+)/g;
@w = /(\w+)/gc;
But if I want to do some lexing then I need /g to enable \G. As long as
I use scalar context that's fine.
if (/(\w)+/gc) {
($foo) = ($1);
but if I want to assign to a list I'm stuck; that would create a list
context indicating I want multiple matches.
if (($foo) = /(\w)+/gc) { # bad
I want to give a list context for assignment to variables and I need \G
to work. With the context overloading of /g that's impossible.
If there was a /l for lexing that enabled \G without adding the global
matching of /g then I'd be happy and I suspect a lot of other people
would stop making the same mistake and bothering you about it.
if (($foo) = /(\w)+/lc) { # bad
Making /gc work so pos wasn't reset on the last, guaranteed to fail,
iteration wouldn't cut it AFAICS. It would still give me multiple
matches which aren't desired.
($foo) = /(\w+)\s*/lc; # takes one word.
($foo) = /(\w+)\s*/gc; # takes many words returning one.
To sum up, /g means two things (many matches and enable \G), it means
you can't just enable \G.
Thanks for your time.
Ralph.
------- End of Forwarded Message
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