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+;;;; Copyright (C) 2000, 2001, 2004, 2006, 2010 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
+;;;;
+
+;;;; A simple value history support
+
+(define-module (ice-9 history)
+ #:export (value-history-enabled? enable-value-history! disable-value-history!
+ clear-value-history!))
+
+(define-module* '(value-history))
+
+(define *value-history-enabled?* #f)
+(define (value-history-enabled?)
+ *value-history-enabled?*)
+
+(define (use-value-history x)
+ (module-use! (current-module)
+ (resolve-interface '(value-history))))
+
+(define save-value-history
+ (let ((count 0)
+ (history (resolve-module '(value-history))))
+ (lambda (v)
+ (if (not (unspecified? v))
+ (let* ((c (1+ count))
+ (s (string->symbol (simple-format #f "$~A" c))))
+ (simple-format #t "~A = " s)
+ (module-define! history s v)
+ (module-export! history (list s))
+ (set! count c))))))
+
+(define (enable-value-history!)
+ (if (not (value-history-enabled?))
+ (begin
+ (add-hook! before-eval-hook use-value-history)
+ (add-hook! before-print-hook save-value-history)
+ (set! *value-history-enabled?* #t))))
+
+(define (disable-value-history!)
+ (if (value-history-enabled?)
+ (begin
+ (remove-hook! before-eval-hook use-value-history)
+ (remove-hook! before-print-hook save-value-history)
+ (set! *value-history-enabled?* #f))))
+
+(define (clear-value-history!)
+ (let ((history (resolve-module '(value-history))))
+ (hash-clear! (module-obarray history))
+ (hash-clear! (module-obarray (module-public-interface history)))))
+
+(enable-value-history!)