Import Upstream version 2a6upstream/2a6

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+; "trnscrpt.scm", transcript functions for Scheme.
+; Copyright (c) 1992, 1993, 1995 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.
+
+(define transcript:port #f)
+
+(define (transcript-on filename)
+  (set! transcript:port (open-output-file filename)))
+
+(define (transcript-off)
+  (if (output-port? transcript:port)
+      (close-output-port transcript:port))
+  (set! transcript:port #f))
+
+(define read-char
+  (let ((read-char read-char) (write-char write-char))
+    (lambda opt
+      (let ((ans (apply read-char opt)))
+	(cond ((eof-object? ans))
+	      ((output-port? transcript:port)
+	       (write-char ans transcript:port)))
+	ans))))
+
+(define read
+  (let ((read read) (write write) (newline newline))
+    (lambda opt
+      (let ((ans (apply read opt)))
+	(cond ((eof-object? ans))
+	      ((output-port? transcript:port)
+	       (write ans transcript:port)
+	       (if (eqv? #\newline (apply peek-char opt))
+		   (newline transcript:port))))
+	ans))))
+
+(define write-char
+  (let ((write-char write-char))
+    (lambda (obj . opt)
+      (apply write-char obj opt)
+      (if (output-port? transcript:port)
+	  (write-char obj transcript:port)))))
+
+(define write
+  (let ((write write))
+    (lambda (obj . opt)
+      (apply write obj opt)
+      (if (output-port? transcript:port)
+	  (write obj transcript:port)))))
+
+(define display
+  (let ((display display))
+    (lambda (obj . opt)
+      (apply display obj opt)
+      (if (output-port? transcript:port)
+	  (display obj transcript:port)))))
+
+(define newline
+  (let ((newline newline))
+    (lambda opt
+      (apply newline opt)
+      (if (output-port? transcript:port)
+	  (newline transcript:port)))))