<' extend sys { !keyed_list: list (key: it) of string; adder() is empty; !num_list: list of int (bits: 5); run() is also { adder(); print num_list; }; }; define "add to list" as computed { if sys.keyed_list.key_exists(<1>) { return("{}"); } else { sys.keyed_list.add(<1>); result = append( "extend sys { adder() is also \ {num_list.add(",<1>,")};}"); }; }; '>