[26826] in Perl-Users-Digest
Perl-Users Digest, Issue: 8856 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Mon Jan 16 09:06:36 2006
Date: Mon, 16 Jan 2006 06:05:04 -0800 (PST)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Mon, 16 Jan 2006 Volume: 10 Number: 8856
Today's topics:
Re: create a hierarchical list from a text file <tadmc@augustmail.com>
Re: ExpatXS: 'Can't call method "read" on an undefined <ebohlman@omsdev.com>
Netiquette aspect <noreply@gunnar.cc>
Re: Netiquette aspect <matthew.garrish@sympatico.ca>
Re: Strategy about browser cache and generated pages <.@.>
while ( ) and until ( ) <j.mapson.nurick@dial.pipex.com>
Re: while ( ) and until ( ) <tassilo.von.parseval@rwth-aachen.de>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Mon, 16 Jan 2006 07:20:26 -0600
From: Tad McClellan <tadmc@augustmail.com>
Subject: Re: create a hierarchical list from a text file
Message-Id: <slrndsn7cp.hlf.tadmc@magna.augustmail.com>
Michael Friendly <friendly@yorku.ca> wrote:
> sub read_items {
> $file = shift;
You should not use global variables without a good reason.
my $file = shift;
> open(IN, $file) || die("cant open $file\n");
You should include the *reason* why the open() failed in your message:
open(IN, $file) || die("cant open '$file' $!");
> undef @items;
If you weren't using a global variable there, then you wouldn't
need to clear it out each time.
You should have
use strict;
in all of your Perl programs, then declare each variable at its first use:
my @items;
> $line =~ s/(\t*)//;
> $level = length($1); # level in tree
You should never use the dollar-digit variables unless you
have ensured that the match *succeeded*, otherwise there
will be a stale, left-over value from some previous match.
my $level = length($1) if $line =~ s/(\t*)//;
But you don't even need regular expressions at all:
my $level = $line =~ tr/\t//d;
> $item = {
> level => $level,
> title => $title,
> url => $url,
> desc => $desc,
> };
> push @items, $item;
You don't need the $item temporary variable if you just us
an anonymous hash constructor in the first place:
push @items, {
level => $level,
title => $title,
url => $url,
desc => $desc,
};
--
Tad McClellan SGML consulting
tadmc@augustmail.com Perl programming
Fort Worth, Texas
------------------------------
Date: 16 Jan 2006 08:53:05 GMT
From: Eric Bohlman <ebohlman@omsdev.com>
Subject: Re: ExpatXS: 'Can't call method "read" on an undefined value' after ca. 500 XML files
Message-Id: <Xns974D1D44CC816ebohlmanomsdevcom@130.133.1.4>
Arvin Portlock <nomail@sorry.com> wrote in
news:dqehgs$auv$1@agate.berkeley.edu:
> The line in question in ExpatXS is this:
>
> $result = $args->{ParseFunc}->($args->{Parser},
> $args->{ParseFuncParam});
>
> In some context that's:
>
> sub _parse_systemid {
> my $self = shift;
> my $fh = IO::File->new(shift);
It appears that the author of the module has committed a classic error of
the sort that posters here are admonished for: opening a file without
checking whether it actually opened. If it didn't, then $fh will be undef
and attempting to call any methods on it will give an error.
> $self->{ParseOptions}->{ParseFunc} = \&ParseStream;
> $self->{ParseOptions}->{ParseFuncParam} = $fh;
> $self->_parse;
> }
------------------------------
Date: Mon, 16 Jan 2006 10:56:37 +0100
From: Gunnar Hjalmarsson <noreply@gunnar.cc>
Subject: Netiquette aspect
Message-Id: <4318qoF1kg12tU1@individual.net>
The netiquette bids us to read the whole thread before posting a reply,
obviously to avoid that the same thing is said repeatedly.[1] That
aspect of the netiquette could be better adhered to, giving us a less
noisy and more to the point clpmisc.
[1] I know that there may be delays in propagating a message to other
Usenet servers, but I have a feeling that unnecessary repetitions are
only in exceptional cases explained by such delays.
--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl
------------------------------
Date: Mon, 16 Jan 2006 07:53:53 -0500
From: "Matt Garrish" <matthew.garrish@sympatico.ca>
Subject: Re: Netiquette aspect
Message-Id: <yHMyf.6774$xk1.129613@news20.bellglobal.com>
"Gunnar Hjalmarsson" <noreply@gunnar.cc> wrote in message
news:4318qoF1kg12tU1@individual.net...
> The netiquette bids us to read the whole thread before posting a reply,
> obviously to avoid that the same thing is said repeatedly.[1] That aspect
> of the netiquette could be better adhered to, giving us a less noisy and
> more to the point clpmisc.
>
What was this born of? You may get four or five identical answers to a
question because four or five people started typing them up at the same
time, but I can't say that I see all that many multi-branch threads where
the exact same advice is being repeated over and over in each branch.
Matt
------------------------------
Date: Mon, 16 Jan 2006 12:34:43 +0100
From: BlinKol <.@.>
Subject: Re: Strategy about browser cache and generated pages
Message-Id: <MPG.1e35a343ca45161f98974e@news.tiscali.fr>
In article <430nl4F1jrs5vU1@individual.net>, noreply@gunnar.cc says...
> Did you notice the instructions at
> http://www.thinkspot.net/ciwac/howtopost.html
>
Not at all. Now, I'm aware of. Thank you, Gunnar.
------------------------------
Date: Mon, 16 Jan 2006 07:49:34 +0000
From: John Nurick <j.mapson.nurick@dial.pipex.com>
Subject: while ( ) and until ( )
Message-Id: <kqims1l8ilcmfirsdapa8m8dg132s7j7tn@4ax.com>
I'm trying to understand why 'while ()' behaves like 'while (1)', but
'until ()' doesn't behave like 'until (1)'. So far - maybe because of
clumsiness with perldoc - I can't find it documented.
This compiles and runs without warnings:
> perl -e "use warnings; while () {$x++; print $x; last if $x==9; }"
123456789
while this won't compile:
> perl -e "use warnings; until () {$x++; print $x; last if $x==9; }"
syntax error at -e line 1, near "() "
syntax error at -e line 1, near "; }"
Execution of -e aborted due to compilation errors.
Could someone please point me to an explanation?
TIA
John
------------------------------
Date: Mon, 16 Jan 2006 10:20:54 +0100
From: "Tassilo v. Parseval" <tassilo.von.parseval@rwth-aachen.de>
Subject: Re: while ( ) and until ( )
Message-Id: <4316rpF1lepv5U1@news.dfncis.de>
Also sprach John Nurick:
> I'm trying to understand why 'while ()' behaves like 'while (1)', but
> 'until ()' doesn't behave like 'until (1)'. So far - maybe because of
> clumsiness with perldoc - I can't find it documented.
>
> This compiles and runs without warnings:
>
> > perl -e "use warnings; while () {$x++; print $x; last if $x==9; }"
> 123456789
>
> while this won't compile:
>
> > perl -e "use warnings; until () {$x++; print $x; last if $x==9; }"
> syntax error at -e line 1, near "() "
> syntax error at -e line 1, near "; }"
> Execution of -e aborted due to compilation errors.
>
> Could someone please point me to an explanation?
It's a subtle difference in Perl's grammar:
/* Loops: while, until, for, and a bare block */
loop : label WHILE '(' remember texpr ')' mintro mblock cont
{ ... }
| label UNTIL '(' remember iexpr ')' mintro mblock cont
{ ... }
Note the distinction into 'texpr' and 'iexpr', the difference being that
'texpr' is an expression where empty means true so 'while ()' is the
same as 'while (1)'.
I am quite sure this has been done on purpose because 'until () { ... }'
would then be the same as 'until (1) { ... }', meaning: the body of the
loop is never executed.
Still, it would be nice to turn 'until ()' into 'until (0)' so a
bug-report (see 'perldoc perlbug') might still be in order here.
Tassilo
--
use bigint;
$n=71423350343770280161397026330337371139054411854220053437565440;
$m=-8,;;$_=$n&(0xff)<<$m,,$_>>=$m,,print+chr,,while(($m+=8)<=200);
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 8856
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