code: func (vm *Engine) curPC() (script int, off int, err error) {
  	err = vm.validPC()
  	if err != nil {
  		return 0, 0, err
  	}
  	return vm.scriptIdx, vm.scriptOff, nil
  }
docs: // curPC returns either the current script and offset, or an error if the
  // position isn't valid.