[27470] in Perl-Users-Digest
Perl-Users Digest, Issue: 9083 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Fri Mar 24 09:05:52 2006
Date: Fri, 24 Mar 2006 06:05:06 -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 Fri, 24 Mar 2006 Volume: 10 Number: 9083
Today's topics:
Re: Code review request. <zen13097@zen.co.uk>
Re: Code review request. <a24061@yahoo.com>
Re: Code review request. <tadmc@augustmail.com>
Re: Great JAPH (was Re: Creating Graphs Dynamically wit jussi.mononen-asdf@asdf-comptel.com
Re: More help requested on permutation code. <jack@abc.net>
Re: More help requested on permutation code. <someone@example.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: 24 Mar 2006 08:59:50 GMT
From: Dave Weaver <zen13097@zen.co.uk>
Subject: Re: Code review request.
Message-Id: <4423b506$0$5190$db0fefd9@news.zen.co.uk>
John W. Krahn <someone@example.com> wrote:
> Dave Weaver wrote:
> > Michael Press <jack@abc.net> wrote:
> >>
> >> printf ("%s\n", join ':', @line), "\n";
> >
> > 'printf (...) interpreted as function at - line 18.'
> >
> > Why enable warnings, only to ignore them?
> >
> > printf "%s\n", join(':', @tokens), "\n"; #(untested)
>
> You have a somewhat similar problem to the OP's code in that the ', "\n"' at
> the end is not doing anything (there is no format in the format string that
> uses that value.)
Oops.
Thank goodness for the "(untested)" caveat. :-/
You're quite right. It should be:
printf "%s\n\n", join(':', @tokens);
or, if you have a distaste for parentheses (which I think, in this
case, help to make things clearer):
printf "%s\n\n", join ':', @tokens;
------------------------------
Date: Fri, 24 Mar 2006 09:20:57 +0000
From: Adam Funk <a24061@yahoo.com>
Subject: Re: Code review request.
Message-Id: <p8qcf3-8io.ln1@news.ducksburg.com>
On 2006-03-23, Tad McClellan <tadmc@augustmail.com> wrote:
> Adam Funk <a24061@yahoo.com> wrote:
>> On 2006-03-23, Dave Weaver <zen13097@zen.co.uk> wrote:
>>
>>> With modern perls "use warnings" is better than -w
>>
>> I didn't know that -- what's the difference?
>
> The first sentence of the description in:
> perldoc warnings
> tells the difference.
--> The "warnings" pragma is a replacement for the command line
--> flag "-w", but the pragma is limited to the enclosing block,
--> while the flag is global. See perllexwarn for more
--> information.
At first, I thought that meant that putting "use warnings" at the
beginning (more or less right after "#!/usr/bin/perl") of a
free-standing Perl program would have the same effect as putting "-w"
on the first line, but on reflection I think that "use warnings"
wouldn't percolate down into module code used by the main program --
is that correct?
------------------------------
Date: Fri, 24 Mar 2006 06:49:35 -0600
From: Tad McClellan <tadmc@augustmail.com>
Subject: Re: Code review request.
Message-Id: <slrne27qmv.3rd.tadmc@magna.augustmail.com>
Adam Funk <a24061@yahoo.com> wrote:
> On 2006-03-23, Tad McClellan <tadmc@augustmail.com> wrote:
>> Adam Funk <a24061@yahoo.com> wrote:
>>> On 2006-03-23, Dave Weaver <zen13097@zen.co.uk> wrote:
>>>
>>>> With modern perls "use warnings" is better than -w
>>>
>>> I didn't know that -- what's the difference?
>>
>> The first sentence of the description in:
>> perldoc warnings
>> tells the difference.
>
> --> The "warnings" pragma is a replacement for the command line
> --> flag "-w", but the pragma is limited to the enclosing block,
> --> while the flag is global. See perllexwarn for more
> --> information.
>
> At first, I thought that meant that putting "use warnings" at the
> beginning (more or less right after "#!/usr/bin/perl") of a
> free-standing Perl program would have the same effect as putting "-w"
> on the first line, but on reflection I think that "use warnings"
> wouldn't percolate down into module code used by the main program --
> is that correct?
Yes, that is correct.
--
Tad McClellan SGML consulting
tadmc@augustmail.com Perl programming
Fort Worth, Texas
------------------------------
Date: Fri, 24 Mar 2006 13:35:21 +0000 (UTC)
From: jussi.mononen-asdf@asdf-comptel.com
Subject: Re: Great JAPH (was Re: Creating Graphs Dynamically with Perl)
Message-Id: <e00sip$65r$1@phys-news4.kolumbus.fi>
>> // > Abigail <abigail@abigail.nl> wrote in
>> // > news:slrne1eb9n.1v0.abigail@alexandra.abigail.nl:
>> // >
>> // > > #!/opt/perl/bin/perl -- # No trailing newline after the last line!
>> // > > BEGIN{$|=$SIG{__WARN__}=sub{$_=$_[0];y-_--;print/(.)"$/;seek _,-open(_
>> // > > ,"+<$0"),2;truncate _,tell _;close _;exec$0}}//rekcaH_lreP_rehtona_tsuJ
>> // >
>> // > This is an amazing JAPH. Very instructive.
>> //
>> // Seconded!
>>
>> The fun is executing the file *twice*.
>
> That was the original reason I thought this one was extremely impressive.
>
> It sure is hard to read ;-)
Thank god for Deparse, we mere mortals would be lost without it.
[tarzan ~]$ perl -MO=Deparse japh.pl
sub BEGIN {
$| = $SIG{'__WARN__'} = sub {
$_ = $_[0];
tr/_/ /;
print /(.)"$/;
seek _, -open(_, "+<$0"), 2;
truncate _, tell _;
close _;
exec $0;
}
;
}
//;
japh.pl syntax OK
That makes much more sense :-)
/jUSSi
--
remove -asdf and asdf- for email address
------------------------------
Date: Fri, 24 Mar 2006 08:55:11 GMT
From: Michael Press <jack@abc.net>
Subject: Re: More help requested on permutation code.
Message-Id: <jack-0990C3.00551124032006@newsclstr02.news.prodigy.com>
In article <aHLUf.1707$B_1.825@edtnps89>,
"John W. Krahn" <someone@example.com> wrote:
> Michael Press wrote:
[...]
> > for (my $idx = $#token_list; $idx >= 0; --$idx)
> > {
> > my $it = $token_list[$idx];
>
> In Perl that is usually written as:
>
> for my $it ( reverse @token_list ) {
I chose not to use `reverse' because I do not want a reversed list,
and reversing a list takes time. Yes? Or does Perl understand
the context and simply feed me the elements in reverse order?
[...]
> > $t = $prev, $prev = $permutation_map{$it}, $permutation_map{$it} = $t;
>
> In Perl that is usually written as:
>
> ( $prev, $permutation_map{$it} ) = ( $permutation_map{$it}, $prev );
I knew that. :)
[...]
> > next if $permutation_map{$key} =~ m/-$/ ;
>
> It _may_ be better to use substr() there (YMMV):
>
> next if substr( $permutation_map{$key}, -1 ) eq '-';
Noted. This is preferable for me and my style.
[...]
> > push @cycles, [@element_list];
> > }
> > for my $key (keys %permutation_map) {$permutation_map{$key} =~ tr/-//d }
>
> In Perl that is usually written as:
>
> tr/-//d for values %permutation_map;
Nifty. Another Perl right to left pipeline.
[...]
> > print join(' ', map { sprintf "(%s)", join ' ', @{$_}} sort {$#{$a} <=> $#{$b}} @cycles ), "\n";
>
> Unless you have changed the value of the $" variable you could write that as:
>
> print join( ' ', map "(@$_)", sort { @$a <=> @$b } @cycles ), "\n";
>
> Or, to extend that to the next level: :-)
>
> print "@{[ map "(@$_)", sort { @$a <=> @$b } @cycles ]}\n";
So what is with the square brackets?
Capture the list with a reference,
then dereference in the print statement to interpolate $".
Yes?
[...]
I also see the
print "@{[ map qq[(@$_)], sort { @$a <=> @$b } @cycles ]}\n";
from your follow up article. Elegant.
Looking at other folks exemplary code is valuable.
Seeing changes to code that I worked over is liberating.
Thanks.
--
Michael Press
------------------------------
Date: Fri, 24 Mar 2006 11:04:39 GMT
From: "John W. Krahn" <someone@example.com>
Subject: Re: More help requested on permutation code.
Message-Id: <bnQUf.4717$K11.2685@clgrps12>
Michael Press wrote:
> In article <aHLUf.1707$B_1.825@edtnps89>,
> "John W. Krahn" <someone@example.com> wrote:
>
>>Michael Press wrote:
>
> [...]
>
>>> for (my $idx = $#token_list; $idx >= 0; --$idx)
>>> {
>>> my $it = $token_list[$idx];
>>In Perl that is usually written as:
>>
>> for my $it ( reverse @token_list ) {
>
> I chose not to use `reverse' because I do not want a reversed list,
> and reversing a list takes time. Yes? Or does Perl understand
> the context and simply feed me the elements in reverse order?
I was just presenting the usual Perl idiom. Your way may in fact be better.
:-)
>>> push @cycles, [@element_list];
>>> }
>>> for my $key (keys %permutation_map) {$permutation_map{$key} =~ tr/-//d }
>>In Perl that is usually written as:
>>
>> tr/-//d for values %permutation_map;
>
> Nifty. Another Perl right to left pipeline.
Not a pipeline, a for loop just like:
for ( values %permutation_map ) { tr/-//d }
but using the for statement modifier. A pipeline would imply something on the
left to collect the modified values:
@permutation_map{ keys %permutation_map } = map { tr/-//d; $_ } values
%permutation_map;
BTW, because hash keys cannot be modified, you could (but probably shouldn't)
write it like this:
tr/-//d for %permutation_map;
>>> print join(' ', map { sprintf "(%s)", join ' ', @{$_}} sort {$#{$a} <=> $#{$b}} @cycles ), "\n";
>>Unless you have changed the value of the $" variable you could write that as:
>>
>> print join( ' ', map "(@$_)", sort { @$a <=> @$b } @cycles ), "\n";
>>
>>Or, to extend that to the next level: :-)
>>
>> print "@{[ map "(@$_)", sort { @$a <=> @$b } @cycles ]}\n";
>
> So what is with the square brackets?
> Capture the list with a reference,
> then dereference in the print statement to interpolate $".
> Yes?
perldoc perlref
[snip]
Here's a trick for interpolating a subroutine call into a string:
print "My sub returned @{[mysub(1,2,3)]} that time.\n";
The way it works is that when the "@{...}" is seen in the double-quoted
string, it's evaluated as a block. The block creates a reference to an
anonymous array containing the results of the call to "mysub(1,2,3)".
So the whole block returns a reference to an array, which is then
dereferenced by "@{...}" and stuck into the double-quoted string. This
chicanery is also useful for arbitrary expressions:
print "That yields @{[$n + 5]} widgets\n";
> I also see the
>
> print "@{[ map qq[(@$_)], sort { @$a <=> @$b } @cycles ]}\n";
>
> from your follow up article. Elegant.
>
> Looking at other folks exemplary code is valuable.
> Seeing changes to code that I worked over is liberating.
Those are just suggestions. Benchmark/profile to determine efficiency of any
code. :-)
John
--
use Perl;
program
fulfillment
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 9083
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