in reply to How can I find out whether a Tk Toplevel widget has been destroyed?

I think you are asking about the Exists method: i'm not an expert but i have use in my Tk Tartaglia's triangle fun - Pascal's triangle fun. Here the relevant part (found in subs: destroy_tri draw_triangle): 
if (! Exists($top_lvl_win)) {
    $top_lvl_win= $mw->Toplevel();

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See also zentara's example: Re: How do I determine if a Tk window exists?
The Exists method is in Widget.


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Re^2: How can I find out whether a Tk Toplevel widget has been destroyed?
by tkguifan (Scribe) on Feb 18, 2015 at 08:47 UTC
    It works for me: 
    use Tk;

my $mw=new MainWindow;

my $toplevel;

my $toplevel_open=0;

my $status=$mw->Label(-text=>'Toplevel Closed :(')->pack;

$mw->repeat(1000,sub
{
    $status->configure(-text=>Exists($toplevel)?
        'Toplevel Open :)':'Toplevel Closed :(');
}
);

sub close_toplevel
{
    return if !Exists($toplevel);
    $toplevel->destroy;
}

$mw->Button(-text=>'Open Toplevel',-command=>
    sub {
        $toplevel=$mw->Toplevel();
    }
)->pack;

$mw->Button(-text=>'Close Toplevel',-command=>\&close_toplevel)->pack;

MainLoop;

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