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;;; object.ss
;;; Copyright (C) 1996 R. Kent Dybvig
;;; from "The Scheme Programming Language, 2ed" by R. Kent Dybvig
;;; Permission is hereby granted, free of charge, to any person obtaining a
;;; copy of this software and associated documentation files (the "Software"),
;;; to deal in the Software without restriction, including without limitation
;;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;;; and/or sell copies of the Software, and to permit persons to whom the
;;; Software is furnished to do so, subject to the following conditions:
;;;
;;; The above copyright notice and this permission notice shall be included in
;;; all copies or substantial portions of the Software.
;;;
;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
;;; THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;;; DEALINGS IN THE SOFTWARE.
;;; define-object creates an object constructor that uses let* to bind
;;; local fields and letrec to define the exported procedures. An
;;; object is itself a procedure that accepts messages corresponding
;;; to the names of the exported procedures. The second pattern is
;;; used to allow the set of local fields to be omitted.
(define-syntax define-object
(syntax-rules ()
((_ (name . varlist)
((var1 val1) ...)
((var2 val2) ...))
(define name
(lambda varlist
(let* ((var1 val1) ...)
(letrec ((var2 val2) ...)
(lambda (msg . args)
(case msg
((var2) (apply var2 args)) ...
(else
(error 'name "invalid message ~s"
(cons msg args))))))))))
((_ (name . varlist)
((var2 val2) ...))
(define-object (name . varlist)
()
((var2 val2) ...)))))
;;; send-message abstracts the act of sending a message from the act
;;; of applying a procedure and allows the message to be unquoted.
(define-syntax send-message
(syntax-rules ()
((_ obj msg arg ...)
(obj 'msg arg ...))))
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