File: debugger.scm

package info (click to toggle)
guile-core 1%3A1.4-24
  • links: PTS
  • area: main
  • in suites: woody
  • size: 6,280 kB
  • ctags: 6,664
  • sloc: ansic: 49,704; lisp: 9,376; sh: 9,209; asm: 1,580; makefile: 696; awk: 198; csh: 50
file content (815 lines) | stat: -rw-r--r-- 24,381 bytes parent folder | download | duplicates (3)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
;;;; Guile Debugger

;;; Copyright (C) 1999 Free Software Foundation, Inc.
;;;
;;; This program is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License as
;;; published by the Free Software Foundation; either version 2, or
;;; (at your option) any later version.
;;;
;;; This program 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
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this software; see the file COPYING.  If not, write to
;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
;;; Boston, MA 02111-1307 USA

(define-module (ice-9 debugger)
  :use-module (ice-9 debug)
  :use-module (ice-9 format)
  :no-backtrace
  )

(if (memq 'readline *features*)
    (define-module (ice-9 debugger)
      :use-module (ice-9 readline)))


(define debugger-prompt "debug> ")

(define-public (debug)
  (let ((stack (fluid-ref the-last-stack)))
    (if stack
	(let ((state (make-state stack 0)))
	  (display "This is the Guile debugger; type \"help\" for help.")
	  (newline)
	  (display "There are ")
	  (write (stack-length stack))
	  (display " frames on the stack.")
	  (newline)
	  (newline)
	  (write-state-short state)
	  (read-and-dispatch-commands state (current-input-port)))
	(display "Nothing to debug.\n"))))

(define (debugger-handler key . args)
  (case key
    ((exit-debugger) #f)
    ((signal)
     ;; Restore stack
     (fluid-set! the-last-stack (fluid-ref before-signal-stack))
     (apply display-error #f (current-error-port) args))
    (else
     (display "Internal debugger error:\n")
     (save-stack debugger-handler)
     (apply throw key args)))
  (throw 'exit-debugger))		;Pop the stack

(define (read-and-dispatch-commands state port)
  (catch 'exit-debugger
    (lambda ()
      (lazy-catch #t
        (lambda ()
	  (with-fluids ((last-command #f))
	    (let loop ((state state))
	      (loop (read-and-dispatch-command state port)))))
	debugger-handler))
    (lambda args
      *unspecified*)))

(define (read-and-dispatch-command state port)
  (if (using-readline?)
      (set-readline-prompt! debugger-prompt)
      (display debugger-prompt))
  (force-output)			;This should not be necessary...
  (let ((token (read-token port)))
    (cond ((eof-object? token)
	   (throw 'exit-debugger))
	  ((not token)
	   (discard-rest-of-line port)
	   (catch-user-errors port (lambda () (run-last-command state))))
	  (else
	   (or (catch-user-errors port
	         (lambda ()
	           (dispatch-command token command-table state port)))
	       state)))))

(define (run-last-command state)
  (let ((procedure (fluid-ref last-command)))
    (if procedure
	(procedure state))))

(define (catch-user-errors port thunk)
  (catch 'debugger-user-error
	 thunk
	 (lambda (key . objects)
	   (apply user-warning objects)
	   (discard-rest-of-line port)
	   #f)))

(define last-command (make-fluid))

(define (user-warning . objects)
  (for-each (lambda (object)
	      (display object))
	    objects)
  (newline))

(define (user-error . objects)
  (apply throw 'debugger-user-error objects))

;;;; Command dispatch

(define (dispatch-command string table state port)
  (let ((value (command-table-value table string)))
    (if value
	(dispatch-command/value value state port)
	(user-error "Unknown command: " string))))

(define (dispatch-command/value value state port)
  (cond ((command? value)
	 (dispatch-command/command value state port))
	((command-table? value)
	 (dispatch-command/table value state port))
	((list? value)
	 (dispatch-command/name value state port))
	(else
	 (error "Unrecognized command-table value: " value))))

(define (dispatch-command/command command state port)
  (let ((procedure (command-procedure command))
	(arguments ((command-parser command) port)))
    (let ((procedure (lambda (state) (apply procedure state arguments))))
      (warn-about-extra-args port)
      (fluid-set! last-command procedure)
      (procedure state))))

(define (warn-about-extra-args port)
  ;; **** modify this to show the arguments.
  (let ((char (skip-whitespace port)))
    (cond ((eof-object? char) #f)
	  ((char=? #\newline char) (read-char port))
	  (else
	   (user-warning "Extra arguments at end of line: "
			 (read-rest-of-line port))))))

(define (dispatch-command/table table state port)
  (let ((token (read-token port)))
    (if (or (eof-object? token)
	    (not token))
	(user-error "Command name too short.")
	(dispatch-command token table state port))))

(define (dispatch-command/name name state port)
  (let ((value (lookup-command name)))
    (cond ((not value)
	   (apply user-error "Unknown command name: " name))
	  ((command-table? value)
	   (apply user-error "Partial command name: " name))
	  (else
	   (dispatch-command/value value state port)))))

;;;; Command definition

(define (define-command name argument-template documentation procedure)
  (let ((name (canonicalize-command-name name)))
    (add-command name
		 (make-command name
			       (argument-template->parser argument-template)
			       documentation
			       procedure)
		 command-table)
    name))

(define (define-command-alias name1 name2)
  (let ((name1 (canonicalize-command-name name1)))
    (add-command name1 (canonicalize-command-name name2) command-table)
    name1))

(define (argument-template->parser template)
  ;; Deliberately handles only cases that occur in "commands.scm".
  (cond ((eq? 'tokens template)
	 (lambda (port)
	   (let loop ((tokens '()))
	     (let ((token (read-token port)))
	       (if (or (eof-object? token)
		       (not token))
		   (list (reverse! tokens))
		   (loop (cons token tokens)))))))
	((null? template)
	 (lambda (port)
	   '()))
	((and (pair? template)
	      (null? (cdr template))
	      (eq? 'object (car template)))
	 (lambda (port)
	   (list (read port))))
	((and (pair? template)
	      (equal? ''optional (car template))
	      (pair? (cdr template))
	      (null? (cddr template)))
	 (case (cadr template)
	   ((token)
	    (lambda (port)
	      (let ((token (read-token port)))
		(if (or (eof-object? token)
			(not token))
		    (list #f)
		    (list token)))))
	   ((exact-integer)
	    (lambda (port)
	      (list (parse-optional-exact-integer port))))
	   ((exact-nonnegative-integer)
	    (lambda (port)
	      (list (parse-optional-exact-nonnegative-integer port))))
	   ((object)
	    (lambda (port)
	      (list (parse-optional-object port))))
	   (else
	    (error "Malformed argument template: " template))))
	(else
	 (error "Malformed argument template: " template))))

(define (parse-optional-exact-integer port)
  (let ((object (parse-optional-object port)))
    (if (or (not object)
	    (and (integer? object)
		 (exact? object)))
	object
	(user-error "Argument not an exact integer: " object))))

(define (parse-optional-exact-nonnegative-integer port)
  (let ((object (parse-optional-object port)))
    (if (or (not object)
	    (and (integer? object)
		 (exact? object)
		 (not (negative? object))))
	object
	(user-error "Argument not an exact non-negative integer: " object))))

(define (parse-optional-object port)
  (let ((terminator (skip-whitespace port)))
    (if (or (eof-object? terminator)
	    (eq? #\newline terminator))
	#f
	(let ((object (read port)))
	  (if (eof-object? object)
	      #f
	      object)))))

;;;; Command tables

(define (lookup-command name)
  (let loop ((table command-table) (strings name))
    (let ((value (command-table-value table (car strings))))
      (cond ((or (not value) (null? (cdr strings))) value)
	    ((command-table? value) (loop value (cdr strings)))
	    (else #f)))))

(define (command-table-value table string)
  (let ((entry (command-table-entry table string)))
    (and entry
	 (caddr entry))))

(define (command-table-entry table string)
  (let loop ((entries (command-table-entries table)))
    (and (not (null? entries))
	 (let ((entry (car entries)))
	   (if (and (<= (cadr entry)
			(string-length string)
			(string-length (car entry)))
		    (= (string-length string)
		       (match-strings (car entry) string)))
	       entry
	       (loop (cdr entries)))))))

(define (match-strings s1 s2)
  (let ((n (min (string-length s1) (string-length s2))))
    (let loop ((i 0))
      (cond ((= i n) i)
	    ((char=? (string-ref s1 i) (string-ref s2 i)) (loop (+ i 1)))
	    (else i)))))

(define (write-command-name name)
  (display (car name))
  (for-each (lambda (string)
	      (write-char #\space)
	      (display string))
	    (cdr name)))

(define (add-command name value table)
  (let loop ((strings name) (table table))
    (let ((entry
	   (or (let loop ((entries (command-table-entries table)))
		 (and (not (null? entries))
		      (if (string=? (car strings) (caar entries))
			  (car entries)
			  (loop (cdr entries)))))
	       (let ((entry (list (car strings) #f #f)))
		 (let ((entries
			(let ((entries (command-table-entries table)))
			  (if (or (null? entries)
				  (string<? (car strings) (caar entries)))
			      (cons entry entries)
			      (begin
				(let loop ((prev entries) (this (cdr entries)))
				  (if (or (null? this)
					  (string<? (car strings) (caar this)))
				      (set-cdr! prev (cons entry this))
				      (loop this (cdr this))))
				entries)))))
		   (compute-string-abbreviations! entries)
		   (set-command-table-entries! table entries))
		 entry))))
      (if (null? (cdr strings))
	  (set-car! (cddr entry) value)
	  (loop (cdr strings)
		(if (command-table? (caddr entry))
		    (caddr entry)
		    (let ((table (make-command-table '())))
		      (set-car! (cddr entry) table)
		      table)))))))

(define (canonicalize-command-name name)
  (cond ((and (string? name)
	      (not (string-null? name)))
	 (list name))
	((let loop ((name name))
	   (and (pair? name)
		(string? (car name))
		(not (string-null? (car name)))
		(or (null? (cdr name))
		    (loop (cdr name)))))
	 name)
	(else
	 (error "Illegal command name: " name))))

(define (compute-string-abbreviations! entries)
  (let loop ((entries entries) (index 0))
    (let ((groups '()))
      (for-each
       (lambda (entry)
	 (let* ((char (string-ref (car entry) index))
		(group (assv char groups)))
	   (if group
	       (set-cdr! group (cons entry (cdr group)))
	       (set! groups
		     (cons (list char entry)
			   groups)))))
       entries)
      (for-each
       (lambda (group)
	 (let ((index (+ index 1)))
	   (if (null? (cddr group))
	       (set-car! (cdadr group) index)
	       (loop (let ((entry
			    (let loop ((entries (cdr group)))
			      (and (not (null? entries))
				   (if (= index (string-length (caar entries)))
				       (car entries)
				       (loop (cdr entries)))))))
		       (if entry
			   (begin
			     (set-car! (cdr entry) index)
			     (delq entry (cdr group)))
			   (cdr group)))
		     index))))
       groups))))

;;;; Data structures

(define command-table-rtd (make-record-type "command-table" '(entries)))
(define make-command-table (record-constructor command-table-rtd '(entries)))
(define command-table? (record-predicate command-table-rtd))
(define command-table-entries (record-accessor command-table-rtd 'entries))
(define set-command-table-entries!
  (record-modifier command-table-rtd 'entries))

(define command-rtd
  (make-record-type "command"
		    '(name parser documentation procedure)))

(define make-command
  (record-constructor command-rtd
		      '(name parser documentation procedure)))

(define command? (record-predicate command-rtd))
(define command-name (record-accessor command-rtd 'name))
(define command-parser (record-accessor command-rtd 'parser))
(define command-documentation (record-accessor command-rtd 'documentation))
(define command-procedure (record-accessor command-rtd 'procedure))

(define state-rtd (make-record-type "debugger-state" '(stack index)))
(define state? (record-predicate state-rtd))
(define make-state (record-constructor state-rtd '(stack index)))
(define state-stack (record-accessor state-rtd 'stack))
(define state-index (record-accessor state-rtd 'index))

(define (new-state-index state index)
  (make-state (state-stack state) index))

;;;; Character parsing

(define (read-token port)
  (letrec
      ((loop
	(lambda (chars)
	  (let ((char (peek-char port)))
	    (cond ((eof-object? char)
		   (do-eof char chars))
		  ((char=? #\newline char)
		   (do-eot chars))
		  ((char-whitespace? char)
		   (do-eot chars))
		  ((char=? #\# char)
		   (read-char port)
		   (let ((terminator (skip-comment port)))
		     (if (eof-object? char)
			 (do-eof char chars)
			 (do-eot chars))))
		  (else
		   (read-char port)
		   (loop (cons char chars)))))))
       (do-eof
	(lambda (eof chars)
	  (if (null? chars)
	      eof
	      (do-eot chars))))
       (do-eot
	(lambda (chars)
	  (if (null? chars)
	      #f
	      (list->string (reverse! chars))))))
    (skip-whitespace port)
    (loop '())))

(define (skip-whitespace port)
  (let ((char (peek-char port)))
    (cond ((or (eof-object? char)
	       (char=? #\newline char))
	   char)
	  ((char-whitespace? char)
	   (read-char port)
	   (skip-whitespace port))
	  ((char=? #\# char)
	   (read-char port)
	   (skip-comment port))
	  (else char))))

(define (skip-comment port)
  (let ((char (peek-char port)))
    (if (or (eof-object? char)
	    (char=? #\newline char))
	char
	(begin
	  (read-char port)
	  (skip-comment port)))))

(define (read-rest-of-line port)
  (let loop ((chars '()))
    (let ((char (read-char port)))
      (if (or (eof-object? char)
	      (char=? #\newline char))
	  (list->string (reverse! chars))
	  (loop (cons char chars))))))

(define (discard-rest-of-line port)
  (let loop ()
    (if (not (let ((char (read-char port)))
	       (or (eof-object? char)
		   (char=? #\newline char))))
	(loop))))

;;;; Commands

(define command-table (make-command-table '()))

(define-command "help" 'tokens
  "Type \"help\" followed by a command name for full documentation."
  (lambda (state tokens)
    (let loop ((name (if (null? tokens) '("help") tokens)))
      (let ((value (lookup-command name)))
	(cond ((not value)
	       (write-command-name name)
	       (display " is not a known command name.")
	       (newline))
	      ((command? value)
	       (display (command-documentation value))
	       (newline)
	       (if (equal? '("help") (command-name value))
		   (begin
		     (display "Available commands are:")
		     (newline)
		     (for-each (lambda (entry)
				 (if (not (list? (caddr entry)))
				     (begin
				       (display "  ")
				       (display (car entry))
				       (newline))))
			       (command-table-entries command-table)))))
	      ((command-table? value)
	       (display "The \"")
	       (write-command-name name)
	       (display "\" command requires a subcommand.")
	       (newline)
	       (display "Available subcommands are:")
	       (newline)
	       (for-each (lambda (entry)
			   (if (not (list? (caddr entry)))
			       (begin
				 (display "  ")
				 (write-command-name name)
				 (write-char #\space)
				 (display (car entry))
				 (newline))))
			 (command-table-entries value)))
	      ((list? value)
	       (loop value))
	      (else
	       (error "Unknown value from lookup-command:" value)))))
    state))

(define-command "frame" '('optional exact-nonnegative-integer)
  "Select and print a stack frame.
With no argument, print the selected stack frame.  (See also \"info frame\").
An argument specifies the frame to select; it must be a stack-frame number."
  (lambda (state n)
    (let ((state (if n (select-frame-absolute state n) state)))
      (write-state-short state)
      state)))

(define-command "position" '()
  "Display the position of the current expression."
  (lambda (state)
    (let* ((frame (stack-ref (state-stack state) (state-index state)))
	   (source (frame-source frame)))
      (if (not source)
	  (display "No source available for this frame.")
	  (let ((position (source-position source)))
	    (if (not position)
		(display "No position information available for this frame.")
		(display-position position)))))
    (newline)
    state))

(define-command "up" '('optional exact-integer)
  "Move N frames up the stack.  For positive numbers N, this advances
toward the outermost frame, to higher frame numbers, to frames
that have existed longer.  N defaults to one."
  (lambda (state n)
    (let ((state (select-frame-relative state (or n 1))))
      (write-state-short state)
      state)))

(define-command "down" '('optional exact-integer)
  "Move N frames down the stack.  For positive numbers N, this
advances toward the innermost frame, to lower frame numbers, to
frames that were created more recently.  N defaults to one."
  (lambda (state n)
    (let ((state (select-frame-relative state (- (or n 1)))))
      (write-state-short state)
      state)))

(define (eval-handler key . args)
  (let ((stack (make-stack #t eval-handler)))
    (if (= (length args) 4)
	(apply display-error stack (current-error-port) args)
	;; We want display-error to be the "final common pathway"
	(catch #t
	       (lambda ()
		 (apply bad-throw key args))
	       (lambda (key . args)
		 (apply display-error stack (current-error-port) args)))))
  (throw 'continue))

(define-command "evaluate" '(object)
  "Evaluate an expression.
The expression must appear on the same line as the command,
however it may be continued over multiple lines."
  (lambda (state expression)
    (let ((source (frame-source (stack-ref (state-stack state)
					   (state-index state)))))
      (if (not source)
	  (display "No environment for this frame.\n")
	  (catch 'continue
		 (lambda ()
		   (lazy-catch #t
			       (lambda ()
				 (let* ((env (memoized-environment source))
					(value (local-eval expression env)))
				   (display ";value: ")
				   (write value)
				   (newline)))
			       eval-handler))
		 (lambda args args)))
      state)))

(define-command "backtrace" '('optional exact-integer)
  "Print backtrace of all stack frames, or innermost COUNT frames.
With a negative argument, print outermost -COUNT frames.
If the number of frames aren't explicitly given, the debug option
`depth' determines the maximum number of frames printed."
  (lambda (state n-frames)
    (let ((stack (state-stack state)))
      ;; Kludge around lack of call-with-values.
      (let ((values
	     (lambda (start end)
	       ;;(do ((index start (+ index 1)))
	       ;;    ((= index end))
	       ;;(write-state-short* stack index))
	       ;;
	       ;; Use builtin backtrace instead:
	       (display-backtrace stack
				  (current-output-port)
				  (if (memq 'backwards (debug-options))
				      start
				      (- end 1))
				  (- end start))
	       )))
	(let ((end (stack-length stack)))
	  (cond ((not n-frames) ;(>= (abs n-frames) end))
		 (values 0 (min end (cadr (memq 'depth (debug-options))))))
		((>= n-frames 0)
		 (values 0 n-frames))
		(else
		 (values (+ end n-frames) end))))))
    state))

(define-command "quit" '()
  "Exit the debugger."
  (lambda (state)
    (throw 'exit-debugger)))

(define-command '("info" "frame") '()
  "All about selected stack frame."
  (lambda (state)
    (write-state-long state)
    state))

(define-command '("info" "args") '()
  "Argument variables of current stack frame."
  (lambda (state)
    (let ((index (state-index state)))
      (let ((frame (stack-ref (state-stack state) index)))
	(write-frame-index-long frame)
	(write-frame-args-long frame)))
    state))

(define-command-alias "f" "frame")
(define-command-alias '("info" "f") '("info" "frame"))
(define-command-alias "bt" "backtrace")
(define-command-alias "where" "backtrace")
(define-command-alias "p" "evaluate")
(define-command-alias '("info" "stack") "backtrace")

;;;; Command Support

(define (select-frame-absolute state number)
  (new-state-index state
		   (frame-number->index
		    (let ((end (stack-length (state-stack state))))
		      (if (>= number end)
			  (- end 1)
			  number))
		    (state-stack state))))

(define (select-frame-relative state delta)
  (new-state-index state
		   (let ((index (+ (state-index state) delta))
			 (end (stack-length (state-stack state))))
		     (cond ((< index 0) 0)
			   ((>= index end) (- end 1))
			   (else index)))))

(define (write-state-short state)
  (display "Frame ")
  (write-state-short* (state-stack state) (state-index state)))

(define (write-state-short* stack index)
  (write-frame-index-short stack index)
  (write-char #\space)
  (write-frame-short (stack-ref stack index))
  (newline))

(define (write-frame-index-short stack index)
  (let ((s (number->string (frame-number (stack-ref stack index)))))
    (display s)
    (write-char #\:)
    (write-chars #\space (- 4 (string-length s)))))

(define (write-frame-short frame)
  (if (frame-procedure? frame)
      (write-frame-short/application frame)
      (write-frame-short/expression frame)))

(define (write-frame-short/application frame)
  (write-char #\[)
  (write (let ((procedure (frame-procedure frame)))
	   (or (and (procedure? procedure)
		    (procedure-name procedure))
	       procedure)))
  (if (frame-evaluating-args? frame)
      (display " ...")
      (begin
	(for-each (lambda (argument)
		    (write-char #\space)
		    (write argument))
		  (frame-arguments frame))
	(write-char #\]))))

;;; Use builtin function instead:
(set! write-frame-short/application
      (lambda (frame)
	(display-application frame (current-output-port) 12)))

(define (write-frame-short/expression frame)
  (write (let* ((source (frame-source frame))
		(copy (source-property source 'copy)))
	   (if (pair? copy)
	       copy
	       (unmemoize source)))))

(define (write-state-long state)
  (let ((index (state-index state)))
    (let ((frame (stack-ref (state-stack state) index)))
      (write-frame-index-long frame)
      (write-frame-long frame))))

(define (write-frame-index-long frame)
  (display "Stack frame: ")
  (write (frame-number frame))
  (if (frame-real? frame)
      (display " (real)"))
  (newline))

(define (write-frame-long frame)
  (if (frame-procedure? frame)
      (write-frame-long/application frame)
      (write-frame-long/expression frame)))

(define (write-frame-long/application frame)
  (display "This frame is an application.")
  (newline)
  (if (frame-source frame)
      (begin
	(display "The corresponding expression is:")
	(newline)
	(display-source frame)
	(newline)))
  (display "The procedure being applied is: ")
  (write (let ((procedure (frame-procedure frame)))
	   (or (and (procedure? procedure)
		    (procedure-name procedure))
	       procedure)))
  (newline)
  (display "The procedure's arguments are")
  (if (frame-evaluating-args? frame)
      (display " being evaluated.")
      (begin
	(display ": ")
	(write (frame-arguments frame))))
  (newline))

(define (display-source frame)
  (let* ((source (frame-source frame))
	 (copy (source-property source 'copy)))
    (cond ((source-position source)
	   => (lambda (p) (display-position p) (display ":\n"))))
    (display "  ")
    (write (or copy (unmemoize source)))))

(define (source-position source)
  (let ((fname (source-property source 'filename))
	(line (source-property source 'line))
	(column (source-property source 'column)))
    (and fname
	 (list fname line column))))

(define (display-position pos)
  (format #t "~A:~D:~D" (car pos) (+ 1 (cadr pos)) (+ 1 (caddr pos))))

(define (write-frame-long/expression frame)
  (display "This frame is an evaluation.")
  (newline)
  (display "The expression being evaluated is:")
  (newline)
  (display-source frame)
  (newline))

(define (write-frame-args-long frame)
  (if (frame-procedure? frame)
      (let ((arguments (frame-arguments frame)))
	(let ((n (length arguments)))
	  (display "This frame has ")
	  (write n)
	  (display " argument")
	  (if (not (= n 1))
	      (display "s"))
	  (write-char (if (null? arguments) #\. #\:))
	  (newline))
	(for-each (lambda (argument)
		    (display "  ")
		    (write argument)
		    (newline))
		  arguments))
      (begin
	(display "This frame is an evaluation frame; it has no arguments.")
	(newline))))

(define (write-chars char n)
  (do ((i 0 (+ i 1)))
      ((>= i n))
    (write-char char)))