Tk with map - Perl newbie

stickleback has asked for the wisdom of the Perl Monks concerning the following question:

I am new to Perl and even newer to Tk. I'm trying to write a login dialog box for a database and learning along the way. I get unexpected behaviour in the following script ...

#/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk 800.000;
use Tk::Dialog;

my $user = "Hello";
my $password = "World";

my $mw = MainWindow->new();
my $dlgLDL = $mw->Dialog(    -title=>'Login',
                            -buttons=>['Ok','Cancel'],
                            -default_button=>'Ok');
my ($fLeft,$fRight) 
    = map {$dlgLDL->Frame(-padx=>4,-borderwidth=>0,-relief=>'groove')-
+>pack(-side=>$_,-pady=>5)}
        qw/left left/;
my ($l1,$l2) 
    = map {$fLeft->Label( -text => $_, -anchor=>'e', -width=>12)->pack
+(-side=>'top',-pady=>3)}
        qw/User: Password: /;
my ($dfHost, $dfPort, $dfUser,$dfPassword) 
    = map {$fRight->Entry(    -textvariable=>$_ )->pack(-side=>'top',-
+pady=>3)}
        qw/\$user \$password/;
my $selected = $dlgLDL->Show();
MainLoop;
[download]

The -textvariable substitution in the third map statement above doesn't do what I hoped, i.e., set up the link to the associated variable. Instead it seems to just place the quoted text into the Entry field. What am I missing?

Please note this may be a very simple mistake as I am still trying to pick up basic Perl syntax.

Comment on Tk with map - Perl newbie Select or Download Code

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Re: Tk with map - Perl newbie by vkon (Curate) on Mar 31, 2011 at 13:40 UTC
by adding unneeded complexity you've lost what is happening why you wrote this way: `my ($dfHost, $dfPort, $dfUser,$dfPassword) = map {$fRight->Entry( -textvariable=>$_ )->pack(-side=>'top',- +pady=>3)} qw/\$user \$password/;` [download] you assign 2-element list to 4 variables, so last two are undefined. But more to the point, if you'll write `$fRight->Entry( -textvariable=>\$user )->pack(-side=>'top',-pady=>3 +); $fRight->Entry( -textvariable=>\$password )->pack(-side=>'top',-pad +y=>3);` [download] your code works as expected. I can not explain it, but I know it :) (addition) `qw/\$user .../` does not do what you want	[reply] [d/l] [select]
Re^2: Tk with map - Perl newbie by stickleback (Novice) on Mar 31, 2011 at 13:56 UTC
Thanks for the quick reply. The 2 element list to 4 variables was a mistake in extracting the dialog from the larger program. Apologies for that. I your suggested broken out code works fine. The following also works ... `$dfUser->configure( -textvariable=>\$user); $dfPassword->configure( -textvariable=>\$password);` [download] I can get my code to work and the dialog to display correctly but I wanted to understand why the original code does not work. I am trying to learn Perl along the way.	[reply] [d/l]
Re^3: Tk with map - Perl newbie by vkon (Curate) on Mar 31, 2011 at 19:20 UTC
(update) deleted wrong content, sorry :-\|	[reply]
Re^3: Tk with map - Perl newbie by Marshall (Canon) on Apr 02, 2011 at 19:22 UTC
The quoting operator as in `qw/\$user \$password/` doesn't work because what is getting translated in to the $_ variable is the TEXT '\$user', not a reference to $user! I show this below with a simple example. Using parens and comma for a normal list allows the \$user to be translated into a value that is the reference. The code will expect to deference the hash value and that will work if what is stored is really a reference to something else rather some text. So in this case, the qw// is not doing what (..,...) does. #!/usr/bin/perl -w use strict; use Data::Dumper; my ($user,$password); my $a=0; my %hash1 = map{$a++=>$_}qw/\$user \$password/; #just text my %hash2 = map{$a++=>$_}(\$user, \$password); #real reference print Dumper \%hash1, \%hash2; $user = 234; $password = 'xyz'; print Dumper \%hash1, \%hash2; __END__ $VAR1 = { '1' => '\\$password', '0' => '\\$user' }; $VAR2 = { '3' => \undef, #ref to an undefined val '2' => \undef }; ################# $VAR1 = { '1' => '\\$password', '0' => '\\$user' }; $VAR2 = { '3' => \'xyz', #see changing $user or $password '2' => \234 #did update the hash #because these are real references. }; [download]	[reply] [d/l] [select]
Re: Tk with map - Perl newbie by Sinistral (Monsignor) on Mar 31, 2011 at 15:12 UTC
As a newbie to both Perl and Tk, I highly recommend the TkDocs site. The tutorial housed there covers multiple OS and multiple programming language issues and comparisons. The Mastering Perl/Tk book is still relevant for the Tk module, but programming best practices have changed and newer Tk libraries/wrappers have been written to take advantage of native operating system widgets to produce better looking and working results. Good luck with your programming!	[reply]
Re^2: Tk with map - Perl newbie by stickleback (Novice) on Mar 31, 2011 at 15:18 UTC
Thanks for the tips.	[reply]
Re^2: Tk with map - Perl newbie by gnosti (Chaplain) on Mar 31, 2011 at 18:19 UTC
Hi, I would like to know about libraries and wrappers that produce better looking results. Could you provide any links? TkDocs doesn't seem to offer much for Perl TK users.	[reply]
Re^3: Tk with map - Perl newbie by Sinistral (Monsignor) on Apr 04, 2011 at 13:57 UTC
Are you sure you've looked at the TkDocs site carefully? They have an excellent guide to installing the current generation Tk on your favorite programming language. In addition, the entire tutorial, starting with the first example includes Tcl, Ruby, Python, and Perl variants of the source. Just look for the code blocks and the camel icon. One thing the site is not, however, is a guide to using Wx, Gtk, Qt4, or even Win32::GUI. If that's what you thought I was saying, I apologize.	[reply]
Re: Tk with map - Perl newbie by Anonymous Monk on Mar 31, 2011 at 13:41 UTC
Do you notice anything about how the Tk demo program "widget" makes use of textvariable? Read more... grep the widget (5 kB) textvariable takes a reference :)	[reply] [d/l]