I don't happen to agree with you on eliminating NIL. I don't understand what the royal pain is. And dynamic-wind is the price you have to pay for call/cc. UNWI

I don't happen to agree with you on eliminating NIL. I don't understand what the royal pain is. And dynamic-wind is the price you have to pay for call/cc. UNWIND-PROTECT is not the same thing. Multi-shot continuations is he reason. One way would be having explicit one-shot continuations and escape continuations. Those are faster and will make UNWIND-PROTECT work. I am more in favour of delimited continuations though. Delimited continuations makes that a bit simpler (since you can easily implement something like dynamic wind using them).