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#lang racket/base
;; Implementation: Have a distinguished frame variable that is read and captured by send/suspend,
;; installed on invocations of continuations by the server (and NOT from other continuation invocations)
(require racket/list
racket/contract)
;; Data types
(define-struct primitive-wc (id))
(define-struct frame (env))
;; Frames
(define *wc-frame* (make-thread-cell (make-frame (make-immutable-hasheq empty)) #t))
(define (current-frame) (thread-cell-ref *wc-frame*))
(define (update-frame! nf) (thread-cell-set! *wc-frame* nf))
;; Web Cell Sets
(define web-cell-set? frame?)
(define (capture-web-cell-set) (current-frame))
(define (restore-web-cell-set! wcs) (update-frame! wcs))
(provide/contract
[web-cell-set? (any/c . -> . boolean?)]
[capture-web-cell-set (-> web-cell-set?)]
[restore-web-cell-set! (web-cell-set? . -> . void)])
;; Web Cells
(define web-cell? primitive-wc?)
(define (make-web-cell default)
(define key (gensym 'web-cell))
(define wc (make-primitive-wc key))
(web-cell-shadow wc default)
wc)
(define (web-cell-ref pwc)
(define i (primitive-wc-id pwc))
(hash-ref
(frame-env (current-frame)) i
(lambda ()
(error 'web-cell "Undefined web-cell: ~.s" i))))
(define (web-cell-shadow wc nv)
(update-frame!
(make-frame
(hash-set (frame-env (current-frame))
(primitive-wc-id wc) nv))))
(provide/contract
[web-cell? (any/c . -> . boolean?)]
[make-web-cell (any/c . -> . web-cell?)]
[web-cell-ref (web-cell? . -> . any/c)]
[web-cell-shadow (web-cell? any/c . -> . void)])
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