in reply to call subroutine if scalar is changed

You can schedule a periodic check for the value using repeat: 
{   my $previous_name = $name;
    $mw->repeat(200, sub {
        if ($name ne $previous_name) {
            warn "$previous_name -> $name";
        }
        $previous_name = $name;
    });
}

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map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In Section Seekers of Perl Wisdom