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+; "repl.scm", read-eval-print-loop for Scheme
+; Copyright (c) 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 (repl:quit) (slib:error "not in repl:repl"))
+
+(define (repl:top-level repl:eval)
+  (repl:repl (lambda () (display "> ")
+		     (force-output (current-output-port))
+		     (read))
+	     repl:eval
+	     (lambda objs
+	       (cond ((null? objs))
+		     (else
+		      (write (car objs))
+		      (for-each (lambda (obj)
+				  (display " ;") (newline) (write obj))
+				(cdr objs))))
+	       (newline))))
+
+(define (repl:repl repl:read repl:eval repl:print)
+  (let* ((old-quit repl:quit)
+	 (old-error slib:error)
+	 (old-eval slib:eval)
+	 (old-load load)
+	 (repl:load (lambda (<pathname>)
+		      (call-with-input-file <pathname>
+			(lambda (port)
+			  (let ((old-load-pathname *load-pathname*))
+			    (set! *load-pathname* <pathname>)
+			    (do ((o (read port) (read port)))
+				((eof-object? o))
+			      (repl:eval o))
+			    (set! *load-pathname* old-load-pathname))))))
+	 (repl:restart #f)
+	 (values? (provided? 'values))
+	 (has-char-ready? (provided? 'char-ready?))
+	 (repl:error (lambda args (require 'debug) (apply qpn args)
+			     (repl:restart #f))))
+    (dynamic-wind
+     (lambda ()
+       (set! load repl:load)
+       (set! slib:eval repl:eval)
+       (set! slib:error repl:error)
+       (set! repl:quit
+	     (lambda () (let ((cont repl:restart))
+			  (set! repl:restart #f)
+			  (cont #t)))))
+     (lambda ()
+       (do () ((call-with-current-continuation
+		(lambda (cont)
+		  (set! repl:restart cont)
+		  (do ((obj (repl:read) (repl:read)))
+		      ((eof-object? obj) (repl:quit))
+		    (cond
+		     (has-char-ready?
+		      (let loop ()
+			(cond ((char-ready?)
+			       (let ((c (peek-char)))
+				 (cond
+				  ((eof-object? c))
+				  ((char=? #\newline c) (read-char))
+				  ((char-whitespace? c)
+				   (read-char) (loop))
+				  (else (newline)))))))))
+		    (if values?
+			(call-with-values (lambda () (repl:eval obj))
+					  repl:print)
+			(repl:print (repl:eval obj)))))))))
+     (lambda () (cond (repl:restart
+		       (display ">>ERROR<<") (newline)
+		       (repl:restart #f)))
+	     (set! load old-load)
+	     (set! slib:eval old-eval)
+	     (set! slib:error old-error)
+	     (set! repl:quit old-quit)))))