Scheme: What is the difference between define and let when used with continutation
continuations, racket, scheme
Solution
In Racket, each top-level expression is wrapped with a prompt.
Since `call/cc` only "captures the current continuation up to the nearest prompt", in your first example, none of the other top-level expressions are captured, so applying `cont2` to `#f` results in just `#f`.
Also, wrapping the first example in `begin` won't change things since a top-level `begin` implicitly splices its contents as if they were top-level expressions.
Problem
I'm wondering the difference between the two following code: ``` (define cont2 #f) (call/cc (lambda (k) (set! cont2 k))) (display "*") (cont2 #f) ``` and ``` (let [(cont #f)] (call/cc (lambda (k) (set! cont k))) (display "*") (cont #f)) ``` In my opinion, the correct behavior of these two programs should be printing '*' infinitely. However, the first one only prints one '*' and exits, while the second one gives the correct behavior. So I'm confused. Is there something special done with `define` or the continuation is not what I thought - all the following programs until the end of the program, it seems to have a boundary or something. Another guess is that the top-level of environment is special treated, like this: ``` (define (test) (define cont2 #f) (call/cc (lambda (k) (set! cont2 k))) (display "*") (cont2 #f)) (test) ``` This works, but why? Thank you for your help!