Thanks 

what is a intervening unwind context?

I'm not sure I understood the question but:

Unwind a context means when you return from a context to an outer one far in the stack you need to check for unwind context (= context with 'ensure:'), and execute the unwind block (= ensure: argument).

For ex:

context 1

context 2

context 3 (marked with primitive as unwind context)

context 4

context 5 Non local return to context 1

Here the non local return in context 5 goes back to context 1 skipping the rest of the execution of the context 2 - 3 - 4. While going back to context 1 it checks every context (2, 3, 4), detects context 3 as unwindcontext and executes the unwind block of context 3 before continuing the execution in context 1. 

 

 

HTH

Eliot

Stef

--
best,

Eliot