在运行时动态组合Boost.Spirit.Qi规则（任意数量的备选方案）

I was wondering whether there is a way in Boost.Spirit.Qi to dynamically combine an arbitrary number of rules at runtime. The inner workings of Boost.Spirit are still a bit of a mystery to me, but since rules are implemented as objects it seems feasible. My motivation is to make certain parts of my grammar easily extendable.I was wondering whether there is a way in Boost