@Override
public Simulation next() {
if (exprIt == null) {
throw new RuntimeException("Iterator not initialised, please call build()");
}
if (current == null || !current.hasNext()) {
if (exprIt.hasNext()) current = exprIt.next();
else throw new NoSuchElementException();
}
return current.next();
}
@Override
public boolean hasNext() {
return exprIt.hasNext() || (current != null && current.hasNext());
}