signature/policy_eval.go
func (pc *PolicyContext) changeState(expected, new policyContextState) error {
	if pc.state != expected {
		return errors.Errorf(`"Invalid PolicyContext state, expected "%s", found "%s"`, expected, pc.state)
	}
	pc.state = new
	return nil
}
func (pc *PolicyContext) changeState(expected, new policyContextState) error {
	if pc.state != expected {
		return errors.Errorf(`"Invalid PolicyContext state, expected "%s", found "%s"`, expected, pc.state)
	}
	pc.state = new
	return nil
}
// changeContextState changes pc.state, or fails if the state is unexpected