Session Type Duality in Java

DualWork.java

import java.util.function.Consumer;
import java.util.function.Function;

public class DualWork {
    // セッション型
    public static class End{
        public End() {}
        public void close() {}
    }
    public static class Send<CONT> {
        public Send(Send<CONT> copy) {}
        public CONT send() { return null; }
    }
    public static class Recv<CONT> {
        public Recv(Recv<CONT> copy) {}
        public CONT recv() { return null; }
    }
    public <S0, T0, S extends S0, T extends T0> Dual<S,T> RECUR(Dual <S0,T0> dual, Function<S0, S> f, Function<T0, T> g) {
        return null;
    }


    // Duality の証拠
    public static abstract class Dual<S,T> {
        public Dual(Dual<S,T> src) {}
        public S startServer(Consumer<T> server) {
            return null;
        }
    }
    public static <S,T> Dual<Send<S>, Recv<T>> SEND(Dual<S,T> cont) {
        return null;
    }
    public static <S1,T1> Dual<Recv<S1>, Send<T1>> RECV(Dual<S1,T1> cont) {
        return null;
    }
    public static Dual<End, End> END() {
        return null;
    }

    public class PingPong extends Send<Recv<PingPong>> {
        public PingPong(Send<Recv<PingPong>> copy) { super(copy); }
    }
    public class PongPing extends Recv<Send<PongPing>> {
        public PongPing(Recv<Send<PongPing>> copy) { super(copy); }
    }

    public class PINGPONG extends Dual<PingPong, PongPing> {
        public PINGPONG() {
            super(RECUR(SEND(RECV(new PINGPONG())), PingPong::new, PongPing::new));
        }
    }
}