You should be able to use RAII to pop things from the stack so that it mirrors the  actual stack. I think.<p>Otherwise, looks pretty good. Interestingly, this doesn&#x27;t contain any unsafe code, probably because Rc and RefCell are doing the actual memory&#x2F;safety management. Still, the purpose of this exercise is to focus on the mark-and-sweep part, and that seems to have been done pretty well here!