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+;;; srfi-111.scm -- SRFI 111 Boxes
+
+;; Copyright (C) 2014 Free Software Foundation, Inc.
+;;
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 3 of the License, or (at your option) any later version.
+;;
+;; This library 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
+;; Lesser General Public License for more details.
+;;
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library; if not, write to the Free Software
+;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+(define-module (srfi srfi-111)
+ #:use-module (srfi srfi-9)
+ #:use-module (srfi srfi-9 gnu)
+ #:export (box box? unbox set-box!))
+
+(cond-expand-provide (current-module) '(srfi-111))
+
+(define-record-type <box>
+ (box value)
+ box?
+ (value unbox set-box!))
+
+(set-record-type-printer! <box>
+ (lambda (box port)
+ (display "#<box " port)
+ (display (number->string (object-address box) 16) port)
+ (display " value: ")
+ (write (unbox box) port)
+ (display ">" port)))