let mut classical_music_app = app::new(); classical_music_app.add_feature(|user, directives, passcode| if user.has_permission(&passcode) && directives.contains("turn a blind eye to") { user.begin_afresh("enjoying former classical masterpieces"); } else { loop { user.listen_to("beethoven's 5th symphony"); if user.feels_satisfied() { break; } } });