Item ExternalVariableReference::evaluateSingleton(const DynamicContext::Ptr &context) const
{
    return context->externalVariableLoader()->evaluateSingleton(m_name, context);
}
bool ExternalVariableReference::evaluateEBV(const DynamicContext::Ptr &context) const
{
    return context->externalVariableLoader()->evaluateEBV(m_name, context);
}
Item::Iterator::Ptr ExternalVariableReference::evaluateSequence(const DynamicContext::Ptr &context) const
{
    Q_ASSERT(context->externalVariableLoader());
    return context->externalVariableLoader()->evaluateSequence(m_name, context);
}