Unless I'm missing something, I don't think you even need to use the after(0,...). You can just call the sub directly.

#!/usr/bin/perl
use Tk;
use Tk::ProgressBar;

my $mw = new Tk::MainWindow;
my $p_bar = $mw->ProgressBar(
             -blocks => 1,
             -width  => 20,
             -length => 200,
             -from   => 0,
             -to     => 100,
             -variable  => \(my $foo),
      )->pack();

$foo = 0;

#$mw->after(0,\&main_logic); 
&main_logic;

MainLoop;

sub main_logic {
$mw->repeat(10, sub { $foo = ($foo + 1) % 100 });
}
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