Actors [ :Helloer :Goodbyer :Changer ] ;

Define SayRepeatedly [
    Remember :Message ;
    Bind [ :Message ] in [ Say @Message ; Again ; ] ;
]

Every :Tick :Helloer  does SayRepeatedly "Hello, " ;
Every :Tick :Goodbyer does SayRepeatedly "Goodbye, " ;
Every :Tick :Worlder  does SayRepeatedly "World!" ;

Every :Tick :Changer does [
    Peek :CurrentScene ; Is HelloWorld ; Then [
        Become :GoodbyeWorld ; Done ;
    ] ;

    Peek :CurrentScene ; Is @goodbye-world ; Then [
        Become :HelloWorld ;
        Remember Current Helloer ;
        Done ;
    ] ;

    Again
] ;

Scenes [ :HelloWorld :GoodbyeWorld ] ;

When :HelloWorld :Started do [
    Create Helloer ;
    Create Worlder ;
    Create Changer ;
] ;

When :GoodbyeWorld :Started do [
    Create Goodbyer ;
    Create Worlder ;
    Create Changer ;
]

Enter HelloWorld ;