ikarus/scheme/ikarus.guardians.ss

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;;; Ikarus Scheme -- A compiler for R6RS Scheme.
;;; Copyright (C) 2006,2007,2008 Abdulaziz Ghuloum
;;;
;;; This program is free software: you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License version 3 as
;;; published by the Free Software Foundation.
;;;
;;; This program is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see <http://www.gnu.org/licenses/>.
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;;; The procedure make-guardian is coped en verbatim
;;; from Dybvig et al. Guardians paper.
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(library (ikarus guardians)
(export make-guardian)
(import (except (ikarus) make-guardian))
(define make-guardian
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(lambda ()
(let ([tc
(let ([x (cons #f #f)])
(cons x x))])
(case-lambda
[()
(and (not (eq? (car tc) (cdr tc)))
(let ([x (car tc)])
(let ([y (car x)])
(set-car! tc (cdr x))
(set-car! x #f)
(set-cdr! x #f)
y)))]
[(obj)
(foreign-call "ikrt_register_guardian_pair" (cons tc obj))
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(void)])))))