experimenting with continuations in racket

main.rkt

#lang racket/base
(define kont #f)
(define my-prompt (make-continuation-prompt-tag))

(begin
  (call-with-continuation-prompt
   (λ ()
     (printf "Before everything~n")
     (printf "The call current/composable returned ~v~n"
             (call/cc
              (lambda (k)
                (printf "Proc started running~n")
                (set! kont k)
                (k k)
                (printf "End of proc~n"))
              my-prompt))
     (printf "After the call itself~n"))
   my-prompt)
  (printf "Outside the prompt~n"))

(call-with-continuation-prompt (lambda () (kont 5)) my-prompt)
(printf "--------------------------~n")

(begin
  (call-with-continuation-prompt
   (λ ()
     (printf "Before everything~n")
     (printf "The call current/composable returned ~v~n"
             (call-with-composable-continuation
              (lambda (k)
                (printf "Proc started running~n")
                (set! kont k)
                (k k)
                (printf "End of proc~n"))
              my-prompt))
     (printf "After the call itself~n"))
   my-prompt)
  (printf "Outside the prompt~n"))

(call-with-continuation-prompt (lambda () (kont 5)) my-prompt)


(printf "--------------------------~n")

(define exit-deep (lambda () (abort-current-continuation my-prompt)))
(define (deep)
  (printf "start deep~n")
  (deeper)
  (printf "end deep~n"))
(define (deeper)
  (printf "start deeper~n")
  (exit-deep)
  (printf "end deeper~n"))
(call-with-continuation-prompt
 deep
 my-prompt
 (lambda () (void)))

(printf "--------------------------~n")
;; using the default handler
(define (raise exn proc)
  (abort-current-continuation
   my-prompt
   (lambda ()
     (when (equal? exn 'the-one-we-are-looking-for)
       (proc)))))
(define (deep2)
  (printf "start deep2~n")
  (deeper2)
  (printf "end deep2~n"))
(define (deeper2)
  (printf "start deeper2~n")
  ; replace 'foo with the other value to see this print
  (raise 'foo (lambda () (printf "default handler calls this~n")))
  (printf "end deeper2~n"))
(call-with-continuation-prompt
 deep2
 my-prompt)


;; understanding call-in-continuation
(printf "--------------------------~n")
(printf "This evaluates to ~v~n"
        (+ 1
           (call/cc (lambda (k) (k 4)))))

(printf "This evaluates to ~v~n"
        (+ 1
           (call/cc (lambda (k)
                      (call-in-continuation k (lambda () 4))))))

;; yea not sure what is happening. see the example in the docs about how dynamic-wind's value is available or something

;; playing with let/cc
(printf "--------------------------~n")
(begin
  (call-with-continuation-prompt
   (λ ()
     (printf "Before everything~n")
     (printf "The call current/composable returned ~v~n"
             (let/cc k
                (printf "Proc started running~n")
                (set! kont k)
                (k k)
                (printf "End of proc~n")))
     (printf "After the call itself~n")))
  (printf "Outside the prompt~n"))