namespace js {
  class StackIter {
    enum State {
      DONE,
      SCRIPTED,
      NATIVE,
      ION 
    };
    State state_;
    void popFrame();
    void popCall();
    void popIonFrame();
    StackIter &operator++();
  };
}
using namespace js;
StackIter & StackIter::operator++() {
  switch (state_) {
    case DONE: __builtin_unreachable();
    case SCRIPTED: popFrame();
    case NATIVE: popCall();
    case ION: popIonFrame();
  }
  return *this;
}