[32185] in Perl-Users-Digest
Perl-Users Digest, Issue: 3450 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Fri Jul 22 06:09:20 2011
Date: Fri, 22 Jul 2011 03:09:04 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Fri, 22 Jul 2011 Volume: 11 Number: 3450
Today's topics:
=?UTF-8?Q?Re=3A_a_little_parsing_challenge_=E2=98=BA?= <xahlee@gmail.com>
Re: a little parsing challenge =?UTF-8?B?4pi6?= <rouslank@msn.com>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: syntax query: ($var++ && next) if /match/ <derykus@gmail.com>
Re: syntax query: ($var++ && next) if /match/ <jurgenex@hotmail.com>
Re: syntax query: ($var++ && next) if /match/ <rweikusat@mssgmbh.com>
Re: syntax query: ($var++ && next) if /match/ <rweikusat@mssgmbh.com>
Re: syntax query: ($var++ && next) if /match/ <derykus@gmail.com>
Re: syntax query: ($var++ && next) if /match/ <bugbear@trim_papermule.co.uk_trim>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 21 Jul 2011 11:53:26 -0700 (PDT)
From: Xah Lee <xahlee@gmail.com>
Subject: =?UTF-8?Q?Re=3A_a_little_parsing_challenge_=E2=98=BA?=
Message-Id: <262ea0fe-1152-42aa-9f5b-93aa76ed6c25@q29g2000prj.googlegroups.com>
On Jul 21, 9:43=C2=A0am, pyt...@bdurham.com wrote:
> Xah,
>
> 1. Is the following string considered legal?
>
> [ { ( ] ) }
>
> Note: Each type of brace opens and closes in the proper sequence. But
> inter-brace opening and closing does not make sense.
nu!
> Or must a closing brace always balance out with the most recent opening
> brace like so?
>
> [ { ( ) } ]
yeah!
> 2. If there are multiple unclosed braces at EOF, is the answer you're
> looking for the position of the first open brace that hasn't been closed
> out yet?
well, as many pointed out, i really haven't thought it out well.
originally, i just want to know the position of a un-matched char.
i haven't taken the time to think about what really should be the
desired behavior. For me, the problem started because i wanted to use
the script to check my 5k html files, in particular, classic novels
that involves double curly quotes and french quotes. So, the desired
behavior is one based on the question of what would best for the user
to see in order to correct a bracket mismatch error in a file. (which,
can get quite complex for nested syntax, because, usually, once you
have one missed, it's all hell from there. I think this is similar to
the problem when a compiler/interpreter encounters a bad syntax in
source code, and thus the poplar situation where error code of
computer programs are hard to understand...)
but anyway, just for this exercise, the requirement needn't be
stringent. I still think that at least the reported position should be
a matching char in the file. (and if we presume this, then only my
code works. LOL)
PS this is a warmup problem for writing a HTML tag validator. I looked
high and lo in past years, but just couldn't find a script that does
simple validation in batch. The w3c one is based on SGML, really huge
amount of un-unstandable irregular historical baggage. XML lexical
validator is much closer, but still not regular. I simply wanted one
just like the match-pair validator in our problem, except the opening
char is not a single char but string of the form <xyz =E2=80=A6> and the
*matching* closing one is of the form </xyz>, and with just one
exception: when a tag has =E2=80=9C/>=E2=80=9D in ending such as <br/> then=
it is
skipped (i.e. not considered as opening or closing).
I'll be writing this soon in elisp=E2=80=A6 since i haven't studied parsers=
, i
had hopes that parser expert would show some proper parser solutions=E2=80=
=A6
in particular i think such can be expressed in Parsing Expression
Grammar in just a few lines=E2=80=A6 but so far no deity came forward to sh=
ow
the light. lol
getting ranty=E2=80=A6 it's funny, somehow the tech geekers all want regex =
to
solve the problem. Regex, regex, regex, a 40 years old deviant bastard
that by some twist of luck became a tool for matching text patterns.
One bloke came forward to show-off a perl regex obfuscation. That's
like, lol. But it might be good for the lulz if his code is actually
complete and worked. Then, you have a few who'd nonchalantly remark
=E2=80=9CO, you just need push-down automata=E2=80=9D. LOL, unless they sho=
w actual
working code, its Automata their asses.
folks, don't get angry with me. I'm a learner. I'm curious. I always
am eager to learn. And there's always things we can learn. Don't get
into a fit and do the troll dance in a pit with me. Nobody's gonna
give a shit if you think u knew it all. If u are not the master of one
thousand and one languages yet, you can learn with me. =E2=98=BA troll!!!!
Xah
------------------------------
Date: Thu, 21 Jul 2011 17:54:15 -0400
From: Rouslan Korneychuk <rouslank@msn.com>
Subject: Re: a little parsing challenge =?UTF-8?B?4pi6?=
Message-Id: <be1Wp.287583$lW4.64964@newsfe07.iad>
On 07/21/2011 09:23 AM, Xah Lee wrote:
> Thanks for the code.
>
> are you willing to make it complete and standalone? i.e. i can run it
> like this:
>
> perl Rouslan_Korneychuk.pl dirPath
>
> and it prints any file that has mismatched pair and line/column number
> or the char position?
>
Since you asked, I put up a complete program at http://pastebin.com/d8GNL0kx
I don't know if it will run on Perl earlier than version 5.10 and I'm
pretty sure it wont run below version 5.8.
Also, I realized that I had completely neglected the case of a closing
bracket that is never opened (e.g. "stuff] stuff"). The program I put on
paste bin has an updated regex that handles this case.
------------------------------
Date: Fri, 22 Jul 2011 02:17:24 -0500
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
Message-Id: <SbGdncgM8eWZubTTnZ2dnUVZ5qidnZ2d@giganews.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.9 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
The article at:
http://www.catb.org/~esr/faqs/smart-questions.html
describes how to get answers from technical people in general.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://www.rehabitation.com/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume that they do
know and are being the "bad kind" of Lazy.
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"top-posting", "Jeopardy" (because the answer comes before the
question), or "TOFU" (Text Over, Fullquote Under).
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"
The above message is a Usenet post.
I don't recall having given anyone permission to use it on a Web site.
------------------------------
Date: Thu, 21 Jul 2011 12:23:19 -0700 (PDT)
From: "C.DeRykus" <derykus@gmail.com>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <73fe73bf-557c-4305-9e96-4b069bb013e1@q29g2000prj.googlegroups.com>
On Jul 21, 9:25=A0am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
> Justin C <justin.1...@purestblue.com> writes:
> > I have:
>
> > #!/usr/bin/perl
>
> > use strict;
> > use warnings;
>
> > my $seen =3D 0;
> > my @arr =3D qw/john paul george ringo/;
>
> > for (@arr) {
> > =A0 =A0($seen =3D 1 && next) if /^paul/;
> > =A0 =A0next unless $seen;
> > =A0 =A0print $_, "\n";
> > }
>
> > __END__
>
> > which prints no output. But if I change the `&&` to a comma it does as
> > expected.... ($seen =3D 1, next) if ...
>
> > I've just read perldoc perlop for Comma Operator, and for &&, but I
> > don't understand why one works and the other doesn't.
>
> The precedence of && is higher than that of =3D, meaning,
>
> $seen =3D 1 && next is equivalent to $seen =3D (1 && next) or (as
> B::Deparse would tell you) $seen =3D next. And next doesn't return a
> value, hence, $seen is never set. The obvious way to fix this:
>
> --------------
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $seen =3D 0;
> my @arr =3D qw/john paul george ringo/;
>
> for (@arr) {
> =A0 =A0 =A0 =A0 (($seen =3D 1) && =A0next) if /^paul/;
> =A0 =A0 =A0 =A0 next unless $seen;
> =A0 =A0 =A0 =A0 print $_, "\n";}
>
> --------------
>
> leads to a particularly useless warning:
>
> [rw@sapphire]/tmp $perl a.pl
> Found =3D in conditional, should be =3D=3D at a.pl line 10.
> george
> ringo
>
> It certainly shouldn't be =3D=3D but I assume that exploiting the
> short-circuiting-ness of && and || for control flow control has
> meanwhile also been declared as 'simply not kosher !!1' by the
> 'rotting Perl'[*] thought police ..
As you noted, $seen never gets any assignment in
the case of $seen =3D next. So I think Perl is just
letting you know something is amiss and its best
guess ("rotten" or not) is that you may have meant
$seen =3D=3D 1 since there's no assignment.
I think a clearer, more direct warning though would
have been something like:
variable $seen is not assigned a value
in expression $seen =3D next.
No lame guess needed.
>
> A half-way German word play: 'modern' is 'modern' in German and adding
> appending a d to that yields modernd <=3D> rotting.
The Gedankenpolizei's warning needs a little
modernizing...
--
Charles DeRykus
------------------------------
Date: Thu, 21 Jul 2011 12:34:29 -0700
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <ikvg27dg2uf9movoloa7k1mcvjps9m7sn8@4ax.com>
Rainer Weikusat <rweikusat@mssgmbh.com> wrote:
>Justin C <justin.1104@purestblue.com> writes:
>> ($seen = 1 && next) if /^paul/;
>
>The precedence of && is higher than that of =, meaning,
>
>$seen = 1 && next is equivalent to $seen = (1 && next) or (as
>B::Deparse would tell you) $seen = next. And next doesn't return a
>value, hence, $seen is never set. The obvious way to fix this:
> (($seen = 1) && next) if /^paul/;
Actually no. The perlish way to do it is to use '&&' for expressions and
'and' for flow control. Then most of the time the precedences will
automatically fall into place.
jue
------------------------------
Date: Thu, 21 Jul 2011 20:35:17 +0100
From: Rainer Weikusat <rweikusat@mssgmbh.com>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <87d3h35swa.fsf@sapphire.mobileactivedefense.com>
Keith Thompson <kst-u@mib.org> writes:
> Rainer Weikusat <rweikusat@mssgmbh.com> writes:
>> Willem <willem@toad.stack.nl> writes:
>>> Rainer Weikusat wrote:
[...]
>>> ) (($seen = 1) && next) if /^paul/;
[...]
>>> ($seen = 1 and next) if /^paul/;
>>
>> Arguably a better idea. But the parenthesises can be dropped as well,
>> making this
>>
>> $seen = 1 and next if /^paul/;
>>
>> which I consider to be preferable.
>
> Some might consider
>
> if (/^paul/) {
> $seen = 1;
> next;
> }
>
> to be preferable.
Or
/^paul/ and $seen = 1, next;
You can put in on several lines if you're afraid your enter key might
feel lonely otherwise
/^paul/
and
$seen
=
1
,
next
;
[SCNR]
Seriously, though, a block in Perl is a separate lexical scope and
this means that executing a conditional block is more expensive than
using a 'non-block' equivalent. When using perl -MO=Conicse,-exec
in order to the a list of 'ops' performed by the Perl code, the
$seen = 1 and next if /^paul/
results in
l </> match(/"^paul"/) s/RTIME
m <|> and(other->n) vK/1
n <$> const[IV 1] s
o <0> padsv[$seen:1,5] sRM*
p <2> sassign sKS/2
q <|> and(other->r) vK/1
r <0> next v*
while the if (...) { } compiles to
l </> match(/"^paul"/) s/RTIME
m <|> and(other->n) vK/1
n <0> enter v
o <;> nextstate(main 3 a.pl:9) v
p <$> const[IV 1] s
q <0> padsv[$seen:1,7] sRM*
r <2> sassign vKS/2
s <;> nextstate(main 3 a.pl:10) v:{
t <0> next v*
u <@> leave vKP
------------------------------
Date: Thu, 21 Jul 2011 20:53:45 +0100
From: Rainer Weikusat <rweikusat@mssgmbh.com>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <8762mv1kc6.fsf@sapphire.mobileactivedefense.com>
"C.DeRykus" <derykus@gmail.com> writes:
> On Jul 21, 9:25 am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
[...]
> The obvious way to fix this:
>>
>> --------------
>> #!/usr/bin/perl
>>
>> use strict;
>> use warnings;
>>
>> my $seen = 0;
>> my @arr = qw/john paul george ringo/;
>>
>> for (@arr) {
>> (($seen = 1) && next) if /^paul/;
>> next unless $seen;
>> print $_, "\n";}
>>
>> --------------
>>
>> leads to a particularly useless warning:
>>
>> [rw@sapphire]/tmp $perl a.pl
>> Found = in conditional, should be == at a.pl line 10.
>> george
>> ringo
[...]
> As you noted, $seen never gets any assignment in
> the case of $seen = next. So I think Perl is just
> letting you know something is amiss and its best
> guess ("rotten" or not) is that you may have meant
> $seen == 1 since there's no assignment.
The broken code compiles without warnings while both working variants
[$seen = 1 and next, ($seen = 1) && next] generate it.
------------------------------
Date: Thu, 21 Jul 2011 17:12:43 -0700 (PDT)
From: "C.DeRykus" <derykus@gmail.com>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <0064d113-0b0b-46ed-b5ec-d68b95399493@u6g2000prc.googlegroups.com>
On Jul 21, 12:53=A0pm, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
> "C.DeRykus" <dery...@gmail.com> writes:
> > On Jul 21, 9:25=A0am, Rainer Weikusat <rweiku...@mssgmbh.com> wrote:
>
> [...]
>
>
>
>
>
>
>
>
>
> > The obvious way to fix this:
>
> >> --------------
> >> #!/usr/bin/perl
>
> >> use strict;
> >> use warnings;
>
> >> my $seen =3D 0;
> >> my @arr =3D qw/john paul george ringo/;
>
> >> for (@arr) {
> >> =A0 =A0 =A0 =A0 (($seen =3D 1) && =A0next) if /^paul/;
> >> =A0 =A0 =A0 =A0 next unless $seen;
> >> =A0 =A0 =A0 =A0 print $_, "\n";}
>
> >> --------------
>
> >> leads to a particularly useless warning:
>
> >> [rw@sapphire]/tmp $perl a.pl
> >> Found =3D in conditional, should be =3D=3D at a.pl line 10.
> >> george
> >> ringo
>
> [...]
>
> > As you noted, $seen never gets =A0any assignment in
> > the case of $seen =3D next. So I think Perl is just
> > letting you know something is amiss and its best
> > guess =A0("rotten" or not) is that you =A0may have meant
> > $seen =3D=3D 1 since there's no assignment.
>
> The broken code compiles without warnings while both working variants
> [$seen =3D 1 and next, ($seen =3D 1) && next] generate it.
You're right...
In summary these two - which don't twist the mind
in strange, unholy ways - do generate the warning:
perl -we"$seen=3D$_=3D0;{($seen=3D1) && next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ $seen=3D1 and next if /^paul/}"
But, these bizarre (or semi-bizarre )ones don't:
perl -we"$seen=3D$_=3D0;{ 1 && next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ 1 and next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ $seen and next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ $seen && next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ $seen=3D=3D1 and next if /^paul/}"
perl -we"$seen=3D$_=3D0;{ $seen=3D=3D1 && next if /^paul/}"
Ideally, I think it'd be nice if Perl would at
least warn that something like {$seen =3D next}
doesn't assign to $seen at all.
--
Charles DeRykus
------------------------------
Date: Fri, 22 Jul 2011 09:40:58 +0100
From: bugbear <bugbear@trim_papermule.co.uk_trim>
Subject: Re: syntax query: ($var++ && next) if /match/
Message-Id: <GMCdnWZpLZAGqrTTnZ2dnUVZ8lSdnZ2d@brightview.co.uk>
Justin C wrote:
>
> I have:
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $seen = 0;
> my @arr = qw/john paul george ringo/;
>
> for (@arr) {
> ($seen = 1&& next) if /^paul/;
> next unless $seen;
> print $_, "\n";
> }
>
> __END__
>
> which prints no output. But if I change the `&&` to a comma it does as
> expected.... ($seen = 1, next) if ...
>
> I've just read perldoc perlop for Comma Operator, and for&&, but I
> don't understand why one works and the other doesn't. Can anyone explain
> this in simple terms?
If your intention is to perform two operations,
relying on the quirk that your first operation
evaluates to "true" is quite dirty.
(I'm deliberately ignoring the operator binding issue,
and addressing intent, here).
If $seen were $absent, with inverted logic, you'd need
to change the operator from && to || which is just horrible.
Perl has perfectly good syntax for "bundling" operations;
abusing (or attempting to abuse) a conditional operator
is not a good idea.
Even if it works.
BugBear
------------------------------
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End of Perl-Users Digest V11 Issue 3450
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