Alternatively, you can use the update() method within the original callback function (and set a delay with the after() method if desired):

sub slide_it {
   my ($c, $thing) = @_;
   for my $i (10..80) {
      $c->coords($thing, $i, $i);
      $c->update;                # update $c widget
      # $c->after(100);          # delay if desired
   }
}
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