我可以使用Scheme中的continuation實現三個函數的共同例程嗎？

Question

是否可以在這裏添加另一個函數procC，以便評估的順序是procA-> procB-> procC-> procA ...？

(define (procA another-fun) 
    (let loop ((n 5)) 
    (display "In Proc A \n") 
    (set! another-fun (call/cc another-fun)) 
    (when (> n 0) 
     (loop (- n 1))))) 

(define (procB another-fun) 
    (let loop ((n 5)) 
    (display "In Proc B \n") 
    (set! another-fun (call/cc another-fun)) 
    (when (> n 0) 
     (loop (- n 1))))) 

Answer 1

從 「Scheme編程語言」

http://www.scheme.com/tspl4/further.html#./further:h3

(define lwp-list '()) ; SO's highlighter gets confused 
(define lwp 
    (lambda (thunk) 
    (set! lwp-list (append lwp-list (list thunk))))) 

(define start 
    (lambda() 
    (let ([p (car lwp-list)]) 
     (set! lwp-list (cdr lwp-list)) 
     (p)))) 

(define pause 
    (lambda() 
    (call/cc 
     (lambda (k) 
     (lwp (lambda() (k #f))) 
     (start))))) 


(lwp (lambda() (let f() (pause) (display "h") (f)))) 
(lwp (lambda() (let f() (pause) (display "e") (f)))) 
(lwp (lambda() (let f() (pause) (display "y") (f)))) 
(lwp (lambda() (let f() (pause) (display "!") (f)))) 
(lwp (lambda() (let f() (pause) (newline) (f)))) 
(start) hey! 
     hey! 
     hey! 
     hey! 

Answer 2

像這樣的事情？

(define (puts . lst) 
    (map display lst) 
    (newline)) 

(define (A some-fun more-fun) 
    (let loop ((n 3)) 
    (puts "In A with " some-fun " and " more-fun " and n=" n) 
    (let-values (((s m) (call/cc (lambda (next-iter) (some-fun more-fun next-iter))))) 
     (set! some-fun s) 
     (set! more-fun m)) 
    (when (> n 0) (loop (- n 1))))) 
(define (B some-fun more-fun) 
    (let loop ((n 3)) 
    (puts "In B with " some-fun " and " more-fun " and n=" n) 
    (let-values (((s m) (call/cc (lambda (next-iter) (some-fun more-fun next-iter))))) 
     (set! some-fun s) 
     (set! more-fun m)) 
    (when (> n 0) (loop (- n 1))))) 
(define (C some-fun more-fun) 
    (let loop ((n 3)) 
    (puts "In C with " some-fun " and " more-fun " and n=" n) 
    (let-values (((s m) (call/cc (lambda (next-iter) (some-fun more-fun next-iter))))) 
     (set! some-fun s) 
     (set! more-fun m)) 
    (when (> n 0) (loop (- n 1))))) 

(A B C)