The following illustrates a use of a stack frame (activation record) that survives the invocation for which it was created.
gc returns a pair of functions, the first of which increments
a counter and the second of which reads it.
The counter is called x and each function pair shares its own x that lives in the persistent frame that was created as the pair creator was invoked.
> (define (gc) (let ((x 0))(cons (lambda () (set! x (+ x 1))) (lambda () x))))
> (define cp1 (gc))
> (define cp2 (gc))
> (define i1 (car cp1))
> (define i2 (car cp2))
> (define r1 (cdr cp1))
> (define r2 (cdr cp2))
> (i1)
> (i1)
> (r2)
0
> (r1)
2
> (i2)
> (r2)
1
>