Generators in Loom

Generators.java

package sandbox;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Consumer;

public class Generators {
    private static final ContinuationScope continuationScope = new ContinuationScope("Generators");

    public static <T> Iterable<T> createGenerator(Consumer<Consumer<T>> consumer) {

        return () -> new Iterator<>() {
            private boolean hasAdvanced;
            private boolean hasNext;
            private T next;

            @Override
            public boolean hasNext() {
                return advance();
            }

            @Override
            public T next() {
                if (advance()) {
                    hasAdvanced = false;
                    return next;
                } else {
                    throw new NoSuchElementException();
                }
            }

            private final Continuation continuation = new Continuation(continuationScope, () -> {
                resetState();
                consumer.accept(this::onNext);
                endOfIterator();
            });

            private void onNext(T value) {
                hasAdvanced = hasNext = true;
                next = value;
                Continuation.yield(continuationScope);
                resetState();
            }

            private void resetState() {
                hasAdvanced = false;
                hasNext = false;
                next = null;
            }

            private void endOfIterator() {
                hasAdvanced = true;
                hasNext = false;
            }

            private boolean advance() {
                if (hasAdvanced) {
                    return hasNext;
                } else if (continuation.isDone()) {
                    return false;
                } else {
                    continuation.run();
                    return hasNext;
                }
            }
        };
    }
}