Second class values are allocated on the run-time stack and they may contain pointers to other values on the stack. The were first discussed in connection with the infamous funarg problem, but then forgotten as heap-allocated closures were discovered.

Recent work has resurrected the interest in second class values as they allow us to safely allocate some data structures (e.g., closures) on the run-time stack. This approach has the advantage of avoiding the cost of garbage collection for these structures as their deallocation is for free when the stack is popped. A system with qualified types ensures that second class values do not escape across stack pops.

We take a second look at this work with the following questions in focus.

• What, exactly, is the meaning of the type qualifiers?
• Can we implement this scheme with a type-based, selective CPS translation?
• Can we extend the formal framework of previous work with first-class and second-class references?