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