[racket] Continuation in embedding Racket

From: Nesterov Kirill (k.v.nesterov at yandex.ru)
Date: Wed Dec 3 15:45:28 EST 2014

Hi all,

I'm trying to embed racket 3m version as interpreter into GUI application. For custom interpreters this application have two required APIs - first one is init and the second one is eval string. So in init I'm calling scheme_register_tls_space and scheme_main_setup after. And in eval I'm using custom version of Racket's read-eval-print-loop without recursion for evaluation of thrings. And everything is working well until I've tried to implement generator. Some reading of sources lead we into problem of continuation. This simple code leads to error "continuation application: attempt to cross a continuation barrier". 

(define (generate-one-element-at-a-time lst)
  (define (control-state return)
     (lambda (element)
               (set! return (call-with-current-continuation
                              (lambda (resume-here)
                                ;; Grab the current continuation
                               (set! control-state resume-here)
                               (return element)))))
    (return 'you-fell-off-the-end))
  (define (generator)
    (call-with-current-continuation control-state)) 
  ;; Return the generator 
(define generate-digit
  (generate-one-element-at-a-time '(0 1 2)))
(generate-digit) ;; 0
(generate-digit) ;; 1 ;; error "continuation application: attempt to cross a continuation barrier"

Attemt to use generators library lead to memory access violation. I suppose the problem lies in stack frames which are cleared every time eval callback from the main program is called. For some reasons I can't run racket in another thread. So may be there is an option how this problem could be solved? May be my assumption is not right? May be switch to CGC and mapping stack with scheme_set_stack_base into heap can help? If it help I can show the source of this plugin.


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