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+;;;; "trace.scm" Utility macros for tracing in Scheme.
+;;; Copyright (C) 1991, 1992, 1993, 1994, 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.
+
+(require 'qp)				;for the qp printer.
+(define debug:indent 0)
+
+(define debug:tracef
+  (let ((null? null?)			;These bindings are so that
+	(not not)			;tracef will not trace parts
+	(car car) (cdr cdr)		;of itself.
+	(eq? eq?) (+ +) (zero? zero?) (modulo modulo)
+	(apply apply) (display display) (qpn qpn))
+    (lambda (function . optname)
+      (set! debug:indent 0)
+      (let ((name (if (null? optname) function (car optname))))
+	(lambda args
+	  (cond ((and (not (null? args))
+		      (eq? (car args) 'debug:untrace-object)
+		      (null? (cdr args)))
+		 function)
+		(else
+		 (do ((i debug:indent (+ -1 i))) ((zero? i)) (display #\ ))
+		 (apply qpn "CALLED" name args)
+		 (set! debug:indent (modulo (+ 1 debug:indent) 8))
+		 (let ((ans (apply function args)))
+		   (set! debug:indent (modulo (+ -1 debug:indent) 8))
+		   (do ((i debug:indent (+ -1 i))) ((zero? i)) (display #\ ))
+		   (qpn "RETURNED" name ans)
+		   ans))))))))
+
+;;; the reason I use a symbol for debug:untrace-object is so
+;;; that functions can still be untraced if this file is read in twice.
+
+(define (debug:untracef function)
+  (set! debug:indent 0)
+  (function 'debug:untrace-object))
+
+;;;;The trace: functions wrap around the debug: functions to provide
+;;; niceties like keeping track of traced functions and dealing with
+;;; redefinition.
+
+(require 'alist)
+(define trace:adder (alist-associator eq?))
+(define trace:deler (alist-remover eq?))
+
+(define *traced-procedures* '())
+(define (trace:tracef fun sym)
+  (cond ((not (procedure? fun))
+	 (display "WARNING: not a procedure " (current-error-port))
+	 (display sym (current-error-port))
+	 (newline (current-error-port))
+	 (set! *traced-procedures* (trace:deler *traced-procedures* sym))
+	 fun)
+	(else
+	 (let ((p (assq sym *traced-procedures*)))
+	   (cond ((and p (eq? (cdr p) fun))
+		  fun)
+		 (else
+		  (let ((tfun (debug:tracef fun sym)))
+		    (set! *traced-procedures*
+			  (trace:adder *traced-procedures* sym tfun))
+		    tfun)))))))
+
+(define (trace:untracef fun sym)
+  (let ((p (assq sym *traced-procedures*)))
+    (set! *traced-procedures* (trace:deler *traced-procedures* sym))
+    (cond ((not (procedure? fun)) fun)
+	  ((not p) fun)
+	  ((eq? (cdr p) fun)
+	   (debug:untracef fun))
+	  (else fun))))
+
+(define tracef debug:tracef)
+(define untracef debug:untracef)
+
+;;;; Finally, the macros trace and untrace
+
+(defmacro trace xs
+  (if (null? xs)
+      `(begin ,@(map (lambda (x) `(set! ,x (trace:tracef ,x ',x)))
+		     (map car *traced-procedures*))
+	      (map car *traced-procedures*))
+      `(begin ,@(map (lambda (x) `(set! ,x (trace:tracef ,x ',x))) xs))))
+(defmacro untrace xs
+  (if (null? xs)
+      (slib:eval
+       `(begin ,@(map (lambda (x) `(set! ,x (trace:untracef ,x ',x)))
+		      (map car *traced-procedures*))
+	       '',(map car *traced-procedures*)))
+      `(begin ,@(map (lambda (x) `(set! ,x (trace:untracef ,x ',x))) xs))))