Right out of mastering perl/tk:

use Tk;

my $mw     = MainWindow->new;
my $c      = $mw->Scrolled('Canvas')->pack();
my $canvas = $c->Subwidget('canvas');
$canvas->CanvasBind("<Button-1>", [ \&print_xy, Ev('x'), Ev('y') ]);
sub print_xy {
  my ($canv, $x, $y) = @_;
  print "(x,y) = ",$canv->canvasx($x),", ",$canv->canvasy($y),"\n";
}
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The code, as is, won't show any window. Why not? I even tried making a $mw label and packing it, but still nothing. What's up?