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+; "withfile.scm", with-input-from-file and with-output-to-file for Scheme
+; Copyright (c) 1992, 1993 Aubrey Jaffer
+;;
+;Permission to copy this software, to redistribute it, and to use it
+;for any purpose is granted, subject to the following restrictions and
+;understandings.
+;
+;1.  Any copy made of this software must include this copyright notice
+;in full.
+;
+;2.  I have made no warrantee or representation that the operation of
+;this software will be error-free, and I am under no obligation to
+;provide any services, by way of maintenance, update, or otherwise.
+;
+;3.  In conjunction with products arising from the use of this
+;material, there shall be no use of my name in any advertising,
+;promotional, or sales literature without prior written consent in
+;each case.
+
+(require 'dynamic-wind)
+
+(define withfile:current-input (current-input-port))
+(define withfile:current-output (current-output-port))
+
+(define (current-input-port) withfile:current-input)
+(define (current-output-port) withfile:current-output)
+
+(define (with-input-from-file file thunk)
+  (define oport withfile:current-input)
+  (define port (open-input-file file))
+  (dynamic-wind (lambda () (set! oport withfile:current-input)
+			   (set! withfile:current-input port))
+		(lambda() (let ((ans (thunk))) (close-input-port port) ans))
+		(lambda() (set! withfile:current-input oport))))
+
+(define (with-output-from-file file thunk)
+  (define oport withfile:current-output)
+  (define port (open-output-file file))
+  (dynamic-wind (lambda() (set! oport withfile:current-output)
+		          (set! withfile:current-output port))
+		(lambda() (let ((ans (thunk))) (close-output-port port) ans))
+		(lambda() (set! withfile:current-output oport))))
+
+(define peek-char
+  (let ((peek-char peek-char))
+    (lambda opt
+      (peek-char (if (null? opt) withfile:current-input (car opt))))))
+
+(define read-char
+  (let ((read-char read-char))
+    (lambda opt
+      (read-char (if (null? opt) withfile:current-input (car opt))))))
+
+(define read
+  (let ((read read))
+    (lambda opt
+      (read (if (null? opt) withfile:current-input (car opt))))))
+
+(define write-char
+  (let ((write-char write-char))
+    (lambda (obj . opt)
+      (write-char obj (if (null? opt) withfile:current-output (car opt))))))
+
+(define write
+  (let ((write write))
+    (lambda (obj . opt)
+      (write obj (if (null? opt) withfile:current-output (car opt))))))
+
+(define display
+  (let ((display display))
+    (lambda (obj . opt)
+      (display obj (if (null? opt) withfile:current-output (car opt))))))
+
+(define newline
+  (let ((newline newline))
+    (lambda opt
+      (newline (if (null? opt) withfile:current-output (car opt))))))
+
+(define force-output
+  (let ((force-output force-output))
+    (lambda opt
+      (force-output (if (null? opt) withfile:current-output (car opt))))))