sub am_i_debugging {
    print "$DB::single\n";
    return (the_debugger_is()) ? 1 : 0;
}

sub the_debugger_is {
    return '-d:ptkdb'
      if(exists $INC{'Devel/ptkdb.pm'});
    return '-d'
      if(exists $INC{'perl5db.pl'});
    return '';
}

print( join("\n",
            am_i_debugging(),
            the_debugger_is(),
            ''));