Incremental Cell

DuelCell.java

public class DuelCell<A,DA> {
    private final A initA;
    private final Stream<DA> sda;
    private final BiFunction<A,DA,A> patchA;
    private final Cell<A> ca;

    public DuelCell(
        A initA,
        Stream<DA> sda,
        BiFunction<A,DA,A> patchA
    ) {
        this.initA = initA;
        this.sda = sda;
        this.patchA = patchA;
        this.ca = sda.accum(initA, (DA da, A a) -> patchA.apply(a, da));
    }

    public <B,DB> DuelCell<B,DB> incMap(BiFunction<B,DB,B> patchB, Function<A,B> nonIncrementalFn, BiFunction<Tuple2<A,DA>,B,DB> incrementalFn) {
        B initB = nonIncrementalFn.apply(ca.sample());
        StreamLoop<Tuple2<B,DB>> slDuelB = new StreamLoop<>();
        Cell<B> cb = slDuelB.map((Tuple2<B,DB> duelB) -> patchB.apply(duelB.a, duelB.b)).hold(initB);
        DuelCell<B,DB> dcb = new DuelCell<>(
            initB,
            sda.snapshot(ca, (DA da, A a) -> new Tuple2<>(a, da)).snapshot(cb, incrementalFn::apply),
            patchB
        );
        slDuelB.loop(dcb.sda.snapshot(dcb.ca, (DB db, B b) -> new Tuple2<>(b, db)));
        return dcb;
    }

    public Cell<A> cell() {
        return ca;
    }

    public Stream<DA> deltaStream() {
        return sda;
    }
}