example.cpp

// Guaranteed to return a value strictly bigger than x (as long as x is finite).
// If x is infinite, will drain the list and then return infinity.
double next(list<double> *const ys, double x)
{
  while (!s->empty())
  {
    double y = /* some computation depending on x and ys->front() */;
    if (y > x)
      return y;
    s->pop_front();
  }
  return infinity();
}

void loop(list<double> const* ys)
{
  double x = -infinity();
  while (!s->empty()) {
    x = next(ys, x);
  }
}