signature/policy_eval.go
func NewPolicyContext(policy *Policy) (*PolicyContext, error) {
	pc := &PolicyContext{Policy: policy, state: pcInitializing}
	// FIXME: initialize
	if err := pc.changeState(pcInitializing, pcReady); err != nil {
		// Huh?! This should never fail, we didn't give the pointer to anybody.
		// Just give up and leave unclean state around.
		return nil, err
	}
	return pc, nil
}
func NewPolicyContext(policy *Policy) (*PolicyContext, error) {
	pc := &PolicyContext{Policy: policy, state: pcInitializing}
	// FIXME: initialize
	if err := pc.changeState(pcInitializing, pcReady); err != nil {
		// Huh?! This should never fail, we didn't give the pointer to anybody.
		// Just give up and leave unclean state around.
		return nil, err
	}
	return pc, nil
}
// NewPolicyContext sets up and initializes a context for the specified policy.
// The policy must not be modified while the context exists. FIXME: make a deep copy?
// If this function succeeds, the caller should call PolicyContext.Destroy() when done.