sunet/scheme/httpd/surflets/callbacks.scm

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;; Copyright 2002, 2003 Andreas Bernauer
;; With callbacks you can create special links that are associated
;; with a function. If the user clicks on the special callback link,
;; the send-html/suspend won't return, but the function will be called
;; instead. Note: It is not sensible to create callbacks on top level,
;; as they contain continuations. You have to create a new callback
;; every time you want to use it (inside a function).
(define (make-callback function)
(call-with-current-continuation
(lambda (exit)
(let* ((req (send/suspend (lambda (new-url)
(exit new-url)))))
(function req)))))
(define (make-annotated-callback function)
(let* ((annotated-address (make-annotated-address))
(dispatch
(lambda (req)
(let ((bindings (get-bindings req)))
(cond
((returned-via annotated-address bindings) =>
(lambda (args)
(apply function (cons req args))))
(else
(error "annotated-callback:
unexpected return values from website"))))))
(callback (make-callback dispatch)))
(lambda args
(annotated-address callback args))))
(define callback-functor
(lambda (req proc . args)
(apply proc (cons req args))))