private static final EvaluationContext INSTANCE = new EvaluationContext();

    private final ThreadLocal<PerThreadContext> threadLocalContext = ThreadLocal.withInitial(() -> new PerThreadContext(null));

    /**
     * Returns the current instance of EvaluationContext for this thread.
     *
     * @return the evaluation context
     */
    public static EvaluationContext current() {
        return INSTANCE;

     */
    protected void beforeRead(EvaluationContext.ScopeContext context, ValueConsumer consumer) {
        beforeRead(context, producer, consumer);
    }

    protected void beforeReadNoProducer(EvaluationContext.ScopeContext context, ValueConsumer consumer) {
        beforeRead(context, null, consumer);
    }

                "block"
            }
        }
    }

    EvaluationContext context() {
        return EvaluationContext.current()
    }

    EvaluationContext.EvaluationOwner createOwner() {
        return Mock(EvaluationContext.EvaluationOwner)
    }

    static interface TestEvaluation extends EvaluationContext.ScopedEvaluation<String, RuntimeException> {}

    private final EvaluationContext.EvaluationOwner owner;
    private final ProviderInternal<?> left;
    @Nullable
    private final ProviderInternal<?> right;
    private final ValueSupplier.ValueProducer leftProducer;
    private final ValueSupplier.ValueProducer rightProducer;

    public OrElseValueProducer(EvaluationContext.ScopeContext context, ProviderInternal<?> left) {

        try (EvaluationContext.ScopeContext ignored = openScope()) {
            return provider.calculatePresence(consumer);
        }
    }

    @Override
    public ExecutionTimeValue<? extends OUT> calculateExecutionTimeValue() {
        try (EvaluationContext.ScopeContext context = openScope()) {

        return type;
    }

    @Override
    public ValueProducer getProducer() {
        try (EvaluationContext.ScopeContext ignored = openScope()) {
            return provider.getProducer();
        }
    }

    @Override
    public ExecutionTimeValue<? extends OUT> calculateExecutionTimeValue() {
        try (EvaluationContext.ScopeContext context = openScope()) {

    protected String toStringNoReentrance() {
        return String.format("and(%s, %s)", left, right);
    }

    @Override
    public boolean calculatePresence(ValueConsumer consumer) {
        try (EvaluationContext.ScopeContext ignored = openScope()) {
            if (!left.calculatePresence(consumer) || !right.calculatePresence(consumer)) {
                return false;
            }
        }

    public boolean calculatePresence(ValueConsumer consumer) {
        try (EvaluationContext.ScopeContext context = openScope()) {
            return backingProvider(context, consumer).calculatePresence(consumer);
        }
    }

    @Override
    protected Value<? extends S> calculateOwnValue(ValueConsumer consumer) {
        try (EvaluationContext.ScopeContext context = openScope()) {

    }

    @Override
    public ValueProducer getProducer() {
        try (EvaluationContext.ScopeContext ignored = openScope()) {
            return provider.getProducer();
        }
    }

    @Override
    public ExecutionTimeValue<? extends T> calculateExecutionTimeValue() {
        try (EvaluationContext.ScopeContext context = openScope()) {

    }

    @Override
    public ValueProducer getProducer() {
        try (EvaluationContext.ScopeContext context = openScope()) {
            return new OrElseValueProducer(context, left, right);
        }
    }

    @Override
    public boolean calculatePresence(ValueConsumer consumer) {
        try (EvaluationContext.ScopeContext ignored = openScope()) {