}

        private void push(EvaluationOwner owner) {
            if (objectsInScope.add(owner)) {
                evaluationStack.add(owner);
            } else {
                throw prepareException(owner);
            }
        }

        private void pop() {
            EvaluationOwner removed = evaluationStack.remove(evaluationStack.size() - 1);
            objectsInScope.remove(removed);
        }