Re: please explain prompt scope

[Matt Wette]

> On Oct 17, 2017, at 5:38 AM, Matt Wette <address@hidden> wrote:
> 
> Here is a program that uses prompt and capture the continuation in top-level 
> binding.
> 
> (define (sf fmt . args) (apply simple-format #t fmt args))
> 
> (define At (make-prompt-tag))
> 
> (define Ak #f)
> 
> (let ((a 2))
>  (call-with-prompt At
>    (lambda ()
>      (sf "hello\n")
>      (abort-to-prompt At)
>      (sf "world where a=~S\n" a))
>    (lambda (k . args)
>      (set! Ak k)
>      (sf "!\n")))
>  (set! a 99))
> 
> (Ak)
> 
> Here is the output:
> hello
> !
> world where a=99
> 
> Can someone explain how `a' is captured in the continuation?
> Does the continuation include the stack outside `prompt'?

I am reading up on this now:
        Sec 9.3 of the Guile 2.2 Manual 
and
        https://www2.ccs.neu.edu/racket/pubs/lasc1990-sf.pdf