1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2004-2025, University of Amsterdam 7 VU University Amsterdam 8 SWI-Prolog Solutions b.v. 9 All rights reserved. 10 11 Redistribution and use in source and binary forms, with or without 12 modification, are permitted provided that the following conditions 13 are met: 14 15 1. Redistributions of source code must retain the above copyright 16 notice, this list of conditions and the following disclaimer. 17 18 2. Redistributions in binary form must reproduce the above copyright 19 notice, this list of conditions and the following disclaimer in 20 the documentation and/or other materials provided with the 21 distribution. 22 23 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 24 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 25 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 26 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 27 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 28 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 29 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 30 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 31 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 33 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 34 POSSIBILITY OF SUCH DAMAGE. 35*/ 36 37:- module(prolog_stack, 38 [ get_prolog_backtrace/2, % +MaxDepth, -Stack 39 get_prolog_backtrace/3, % +MaxDepth, -Stack, +Options 40 prolog_stack_frame_property/2, % +Frame, ?Property 41 print_prolog_backtrace/2, % +Stream, +Stack 42 print_prolog_backtrace/3, % +Stream, +Stack, +Options 43 backtrace/1, % +MaxDepth 44 print_last_choicepoint/0, 45 print_last_choicepoint/2 % +Choice, +Options 46 ]). 47:- use_module(library(debug),[debug/3]). 48:- autoload(library(error),[must_be/2]). 49:- autoload(library(lists),[nth1/3,append/3]). 50:- autoload(library(option),[option/2,option/3,merge_options/3]). 51:- autoload(library(prolog_clause), 52 [clause_name/2,predicate_name/2,clause_info/4]). 53 54 55:- dynamic stack_guard/1. 56:- multifile stack_guard/1. 57 58:- predicate_options(print_prolog_backtrace/3, 3, 59 [ subgoal_positions(boolean), 60 show_file(oneof([absolute, basename])) 61 ]).
93:- create_prolog_flag(backtrace, true, [type(boolean), keep(true)]). 94:- create_prolog_flag(backtrace_depth, 20, [type(integer), keep(true)]). 95:- create_prolog_flag(backtrace_goal_depth, 3, [type(integer), keep(true)]). 96:- create_prolog_flag(backtrace_show_lines, true, [type(boolean), keep(true)]).
backtrace_goal_depth, set to 3 initially, showing the
goal and toplevel of any argument.Clause+PC or as a location term that
does not use clause references, allowing the exception to
be printed safely in a different context.129get_prolog_backtrace(MaxDepth, Stack) :- 130 get_prolog_backtrace(MaxDepth, Stack, []). 131 132get_prolog_backtrace(Fr, MaxDepth, Stack) :- 133 integer(Fr), integer(MaxDepth), var(Stack), 134 !, 135 get_prolog_backtrace_lc(MaxDepth, Stack, [frame(Fr)]), 136 nlc. 137get_prolog_backtrace(MaxDepth, Stack, Options) :- 138 get_prolog_backtrace_lc(MaxDepth, Stack, Options), 139 nlc. % avoid last-call-optimization, such that 140 % the top of the stack is always a nice Prolog 141 % frame 142 143nlc. 144 145get_prolog_backtrace_lc(MaxDepth, Stack, Options) :- 146 ( option(frame(Fr), Options) 147 -> PC = call 148 ; prolog_current_frame(Fr0), 149 prolog_frame_attribute(Fr0, pc, PC), 150 prolog_frame_attribute(Fr0, parent, Fr) 151 ), 152 ( option(goal_term_depth(GoalDepth), Options) 153 -> true 154 ; current_prolog_flag(backtrace_goal_depth, GoalDepth) 155 ), 156 option(guard(Guard), Options, none), 157 ( def_no_clause_refs(Guard) 158 -> DefClauseRefs = false 159 ; DefClauseRefs = true 160 ), 161 option(clause_references(ClauseRefs), Options, DefClauseRefs), 162 must_be(nonneg, GoalDepth), 163 backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, Stack, Options). 164 165def_no_clause_refs(system:catch_with_backtrace/3). 166 167backtrace(0, _, _, _, _, _, [], _) :- !. 168backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, 169 [frame(Level, Where, Goal)|Stack], Options) :- 170 prolog_frame_attribute(Fr, level, Level), 171 ( PC == foreign 172 -> prolog_frame_attribute(Fr, predicate_indicator, Pred), 173 Where = foreign(Pred) 174 ; PC == call 175 -> prolog_frame_attribute(Fr, predicate_indicator, Pred), 176 Where = call(Pred) 177 ; prolog_frame_attribute(Fr, clause, Clause) 178 -> clause_where(ClauseRefs, Clause, PC, Where, Options) 179 ; Where = meta_call 180 ), 181 ( Where == meta_call 182 -> Goal = 0 183 ; copy_goal(GoalDepth, Fr, Goal) 184 ), 185 ( prolog_frame_attribute(Fr, pc, PC2) 186 -> true 187 ; PC2 = foreign 188 ), 189 ( prolog_frame_attribute(Fr, parent, Parent), 190 prolog_frame_attribute(Parent, predicate_indicator, PI), 191 PI == Guard % last frame 192 -> backtrace(1, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) 193 ; prolog_frame_attribute(Fr, parent, Parent), 194 more_stack(Parent) 195 -> D2 is MaxDepth - 1, 196 backtrace(D2, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) 197 ; Stack = [] 198 ). 199 200more_stack(Parent) :- 201 prolog_frame_attribute(Parent, predicate_indicator, PI), 202 \+ ( PI = ('$toplevel':G), 203 G \== (toplevel_call/1) 204 ), 205 !. 206more_stack(_) :- 207 current_prolog_flag(break_level, Break), 208 Break >= 1.
true, this is the a term
clause(Clause,PC), providing all abvailable information to the
caller at low time overhead. If however the exception need to be
printed in an environment where the clause references may differ,
for example because the program is not loaded, it is printed in a
different thread and contains references to dynamic predicates, etc,
it is better to use the information inside the clause here.221clause_where(true, Clause, PC, clause(Clause, PC), _). 222clause_where(false, Clause, PC, pred_line(PredName, File:Line), Options) :- 223 option(subgoal_positions(true), Options, true), 224 subgoal_position(Clause, PC, File, CharA, _CharZ), 225 File \= @(_), % XPCE Object reference 226 lineno(File, CharA, Line), 227 clause_predicate_name(Clause, PredName), 228 !. 229clause_where(false, Clause, _PC, pred_line(PredName, File:Line), _Options) :- 230 clause_property(Clause, file(File)), 231 clause_property(Clause, line_count(Line)), 232 clause_predicate_name(Clause, PredName), 233 !. 234clause_where(false, Clause, _PC, clause_name(ClauseName), _Options) :- 235 clause_name(Clause, ClauseName).
name(A1, ..., A16, <skipped Skipped of Arity>, An)
247copy_goal(0, _, 0) :- !. % 0 is not a valid goal 248copy_goal(D, Fr, Goal) :- 249 prolog_frame_attribute(Fr, goal, Goal0), 250 ( Goal0 = Module:Goal1 251 -> copy_term_limit(D, Goal1, Goal2), 252 ( hidden_module(Module) 253 -> Goal = Goal2 254 ; Goal = Module:Goal2 255 ) 256 ; copy_term_limit(D, Goal0, Goal) 257 ). 258 (system). 260hidden_module(user). 261 262copy_term_limit(0, In, '...') :- 263 compound(In), 264 !. 265copy_term_limit(N, In, Out) :- 266 is_dict(In), 267 !, 268 dict_pairs(In, Tag, PairsIn), 269 N2 is N - 1, 270 MaxArity = 16, 271 copy_pairs(PairsIn, N2, MaxArity, PairsOut), 272 dict_pairs(Out, Tag, PairsOut). 273copy_term_limit(N, In, Out) :- 274 compound(In), 275 !, 276 compound_name_arity(In, Functor, Arity), 277 N2 is N - 1, 278 MaxArity = 16, 279 ( Arity =< MaxArity 280 -> compound_name_arity(Out, Functor, Arity), 281 copy_term_args(0, Arity, N2, In, Out) 282 ; OutArity is MaxArity+2, 283 compound_name_arity(Out, Functor, OutArity), 284 copy_term_args(0, MaxArity, N2, In, Out), 285 SkipArg is MaxArity+1, 286 Skipped is Arity - MaxArity - 1, 287 format(atom(Msg), '<skipped ~D of ~D>', [Skipped, Arity]), 288 arg(SkipArg, Out, Msg), 289 arg(Arity, In, InA), 290 arg(OutArity, Out, OutA), 291 copy_term_limit(N2, InA, OutA) 292 ). 293copy_term_limit(_, In, Out) :- 294 copy_term_nat(In, Out). 295 296copy_term_args(I, Arity, Depth, In, Out) :- 297 I < Arity, 298 !, 299 I2 is I + 1, 300 arg(I2, In, InA), 301 arg(I2, Out, OutA), 302 copy_term_limit(Depth, InA, OutA), 303 copy_term_args(I2, Arity, Depth, In, Out). 304copy_term_args(_, _, _, _, _). 305 306copy_pairs([], _, _, []) :- !. 307copy_pairs(Pairs, _, 0, ['<skipped>'-Skipped]) :- 308 !, 309 length(Pairs, Skipped). 310copy_pairs([K-V0|T0], N, MaxArity, [K-V|T]) :- 311 copy_term_limit(N, V0, V), 312 MaxArity1 is MaxArity - 1, 313 copy_pairs(T0, N, MaxArity1, T).
level(Level)predicate(PI)location(File:Line)326prolog_stack_frame_property(frame(Level,_,_), level(Level)). 327prolog_stack_frame_property(frame(_,Where,_), predicate(PI)) :- 328 frame_predicate(Where, PI). 329prolog_stack_frame_property(frame(_,clause(Clause,PC),_), location(File:Line)) :- 330 subgoal_position(Clause, PC, File, CharA, _CharZ), 331 File \= @(_), % XPCE Object reference 332 lineno(File, CharA, Line). 333prolog_stack_frame_property(frame(_,_,_,Goal), goal(Goal)) :- 334 Goal \== 0. 335 336 337frame_predicate(foreign(PI), PI). 338frame_predicate(call(PI), PI). 339frame_predicate(clause(Clause, _PC), PI) :- 340 clause_property(Clause, predicate(PI)). 341 342default_backtrace_options(Options) :- 343 ( current_prolog_flag(backtrace_show_lines, true), 344 current_prolog_flag(iso, false) 345 -> Options = [] 346 ; Options = [subgoal_positions(false)] 347 ).
true. print subgoal line numbers. The default depends
on the Prolog flag backtrace_show_lines.absolute or
basename.364print_prolog_backtrace(Stream, Backtrace) :- 365 print_prolog_backtrace(Stream, Backtrace, []). 366 367print_prolog_backtrace(Stream, Backtrace, Options) :- 368 default_backtrace_options(DefOptions), 369 merge_options(Options, DefOptions, FinalOptions), 370 phrase(message(Backtrace, FinalOptions), Lines), 371 print_message_lines(Stream, '', Lines). 372 373:- public % Called from some handlers 374 message//1. 375 376message(Backtrace) --> 377 {default_backtrace_options(Options)}, 378 message(Backtrace, Options). 379 380message(Backtrace, Options) --> 381 message_frames(Backtrace, Options), 382 warn_nodebug(Backtrace). 383 384message_frames([], _) --> 385 []. 386message_frames([H|T], Options) --> 387 message_frames(H, Options), 388 ( {T == []} 389 -> [] 390 ; [nl], 391 message_frames(T, Options) 392 ). 393 394message_frames(frame(Level, Where, 0), Options) --> 395 !, 396 level(Level), 397 where_no_goal(Where, Options). 398message_frames(frame(Level, _Where, '$toplevel':toplevel_call(_)), _) --> 399 !, 400 level(Level), 401 [ '<user>'-[] ]. 402message_frames(frame(Level, Where, Goal), Options) --> 403 level(Level), 404 [ ansi(code, '~p', [Goal]) ], 405 where_goal(Where, Options). 406 407where_no_goal(foreign(PI), _) --> 408 [ '~w <foreign>'-[PI] ]. 409where_no_goal(call(PI), _) --> 410 [ '~w'-[PI] ]. 411where_no_goal(pred_line(PredName, File:Line), Options) --> 412 !, 413 [ '~w at '-[PredName] ], file_line(File:Line, Options). 414where_no_goal(clause_name(ClauseName), _) --> 415 !, 416 [ '~w <no source>'-[ClauseName] ]. 417where_no_goal(clause(Clause, PC), Options) --> 418 { nonvar(Clause), 419 !, 420 clause_where(false, Clause, PC, Where, Options) 421 }, 422 where_no_goal(Where, Options). 423where_no_goal(meta_call, _) --> 424 [ '<meta call>' ]. 425 426where_goal(foreign(_), _) --> 427 [ ' <foreign>'-[] ], 428 !. 429where_goal(pred_line(_PredName, File:Line), Options) --> 430 !, 431 [ ' at ' ], file_line(File:Line, Options). 432where_goal(clause_name(ClauseName), _) --> 433 !, 434 [ '~w <no source>'-[ClauseName] ]. 435where_goal(clause(Clause, PC), Options) --> 436 { nonvar(Clause), 437 !, 438 clause_where(false, Clause, PC, Where, Options) 439 }, 440 where_goal(Where, Options). 441where_goal(clause(Clause, _PC), _) --> 442 { clause_property(Clause, file(File)), 443 clause_property(Clause, line_count(Line)) 444 }, 445 !, 446 [ ' at ', url(File:Line) ]. 447where_goal(clause(Clause, _PC), _) --> 448 { clause_name(Clause, ClauseName) 449 }, 450 !, 451 [ ' ~w <no source>'-[ClauseName] ]. 452where_goal(_, _) --> 453 []. 454 455level(Level) --> 456 [ ansi(bold, '~|~t[~D]~6+ ', [Level]) ]. 457 458file_line(File:Line, Options), option(show_files(basename), Options) ==> 459 { file_base_name(File, Base), 460 format(string(Label), '~w:~d', [Base, Line]) 461 }, 462 [ url(File:Line, Label) ]. 463file_line(File:Line, _Options) ==> 464 [ url(File:Line) ]. 465 466warn_nodebug(Backtrace) --> 467 { contiguous(Backtrace) }, 468 !. 469warn_nodebug(_Backtrace) --> 470 [ nl,nl, 471 'Note: some frames are missing due to last-call optimization.'-[], nl, 472 'Re-run your program in debug mode (:- debug.) to get more detail.'-[] 473 ]. 474 475contiguous([frame(D0,_,_)|Frames]) :- 476 contiguous(Frames, D0). 477 478contiguous([], _). 479contiguous([frame(D1,_,_)|Frames], D0) :- 480 D1 =:= D0-1, 481 contiguous(Frames, D1).
489:- multifile 490 user:prolog_clause_name/2. 491 492clause_predicate_name(Clause, PredName) :- 493 user:prolog_clause_name(Clause, PredName), 494 !. 495clause_predicate_name(Clause, PredName) :- 496 nth_clause(Head, _N, Clause), 497 !, 498 predicate_name(user:Head, PredName).
505backtrace(MaxDepth) :- 506 get_prolog_backtrace_lc(MaxDepth, Stack, []), 507 print_prolog_backtrace(user_error, Stack). 508 509 510subgoal_position(ClauseRef, PC, File, CharA, CharZ) :- 511 debug(backtrace, 'Term-position in ~p at PC=~w:', [ClauseRef, PC]), 512 clause_info(ClauseRef, File, TPos, _), 513 '$clause_term_position'(ClauseRef, PC, List), 514 debug(backtrace, '\t~p~n', [List]), 515 find_subgoal(List, TPos, PosTerm), 516 compound(PosTerm), 517 arg(1, PosTerm, CharA), 518 arg(2, PosTerm, CharZ).
524find_subgoal(_, Pos, Pos) :- 525 var(Pos), 526 !. 527find_subgoal([A|T], term_position(_, _, _, _, PosL), SPos) :- 528 nth1(A, PosL, Pos), 529 !, 530 find_subgoal(T, Pos, SPos). 531find_subgoal([1|T], brace_term_position(_,_,Pos), SPos) :- 532 !, 533 find_subgoal(T, Pos, SPos). 534find_subgoal(List, parentheses_term_position(_,_,Pos), SPos) :- 535 !, 536 find_subgoal(List, Pos, SPos). 537find_subgoal(_, Pos, Pos).
546lineno(File, Char, Line) :- 547 setup_call_cleanup( 548 ( prolog_clause:try_open_source(File, Fd), 549 set_stream(Fd, newline(detect)) 550 ), 551 lineno_(Fd, Char, Line), 552 close(Fd)). 553 554lineno_(Fd, Char, L) :- 555 stream_property(Fd, position(Pos)), 556 stream_position_data(char_count, Pos, C), 557 C > Char, 558 !, 559 stream_position_data(line_count, Pos, L0), 560 L is L0-1. 561lineno_(Fd, Char, L) :- 562 skip(Fd, 0'\n), 563 lineno_(Fd, Char, L). 564 565 566 /******************************* 567 * CHOICEPOINTS * 568 *******************************/
574print_last_choicepoint :- 575 prolog_current_choice(ChI0), % Choice in print_last_choicepoint/0 576 prolog_choice_attribute(ChI0, parent, ChI1), 577 print_last_choicepoint(ChI1, []). 578print_last_choicepoint.
582print_last_choicepoint(ChI1, Options) :- 583 real_choice(ChI1, ChI), 584 prolog_choice_attribute(ChI, frame, F), 585 prolog_frame_attribute(F, goal, Goal), 586 Goal \= '$execute_goal2'(_,_,_), % Toplevel REPL choicepoint 587 !, 588 option(message_level(Level), Options, warning), 589 get_prolog_backtrace(2, [_|Stack], [frame(F)]), 590 ( predicate_property(Goal, foreign) 591 -> print_message(Level, choicepoint(foreign(Goal), Stack)) 592 ; prolog_frame_attribute(F, clause, Clause), 593 ( prolog_choice_attribute(ChI, pc, PC) 594 -> Ctx = jump(PC) 595 ; prolog_choice_attribute(ChI, clause, Next) 596 -> Ctx = clause(Next) 597 ), 598 print_message(Level, choicepoint(clause(Goal, Clause, Ctx), Stack)) 599 ). 600print_last_choicepoint(_, _). 601 602real_choice(Ch0, Ch) :- 603 prolog_choice_attribute(Ch0, type, Type), 604 dummy_type(Type), 605 !, 606 prolog_choice_attribute(Ch0, parent, Ch1), 607 real_choice(Ch1, Ch). 608real_choice(Ch, Ch). 609 610dummy_type(debug). 611dummy_type(none). 612 613prologmessage(choicepoint(Choice, Stack)) --> 614 choice(Choice), 615 [ nl, 'Called from', nl ], 616 message(Stack). 617 618choice(foreign(Goal)) --> 619 success_goal(Goal, 'a foreign choice point'). 620choice(clause(Goal, ClauseRef, clause(Next))) --> 621 success_goal(Goal, 'a choice point in alternate clause'), 622 [ nl ], 623 [ ' ' ], clause_descr(ClauseRef), [': clause succeeded', nl], 624 [ ' ' ], clause_descr(Next), [': next candidate clause' ]. 625choice(clause(Goal, ClauseRef, jump(PC))) --> 626 { clause_where(false, ClauseRef, PC, Where, 627 [subgoal_positions(true)]) 628 }, 629 success_goal(Goal, 'an in-clause choice point'), 630 [ nl, ' ' ], 631 where_no_goal(Where). 632 633success_goal(Goal, Reason) --> 634 [ ansi(code, '~p', [Goal]), 635 ' left ~w (after success)'-[Reason] 636 ]. 637 638where_no_goal(pred_line(_PredName, File:Line)) --> 639 !, 640 [ url(File:Line) ]. 641where_no_goal(clause_name(ClauseName)) --> 642 !, 643 [ '~w <no source>'-[ClauseName] ]. 644 645clause_descr(ClauseRef) --> 646 { clause_property(ClauseRef, file(File)), 647 clause_property(ClauseRef, line_count(Line)) 648 }, 649 !, 650 [ url(File:Line) ]. 651clause_descr(ClauseRef) --> 652 { clause_name(ClauseRef, Name) 653 }, 654 [ '~w'-[Name] ]. 655 656 657 /******************************* 658 * DECORATE ERRORS * 659 *******************************/
none if the exception is not caught
and with a fully qualified (e.g., Module:Name/Arity) predicate
indicator of the predicate that called catch/3 if the exception
is caught.
The exception is of the form error(Formal, ImplDef) and this
hook succeeds, ImplDef is unified to a term
context(prolog_stack(StackData), Message). This context
information is used by the message printing system to print a
human readable representation of the stack when the exception
was raised.
For example, using a clause stack_guard(none) prints contexts
for uncaught exceptions only. Using a clause stack_guard(_)
prints a full stack-trace for any error exception if the
exception is given to print_message/2. See also
library(http/http_error), which limits printing of exceptions to
exceptions in user-code called from the HTTP server library.
Details of the exception decoration is controlled by two Prolog flags:
true.695:- multifile prolog:prolog_exception_hook/5. 696:- dynamic prolog:prolog_exception_hook/5. 697 698prolog:prolog_exception_hook(error(E, context(Ctx0,Msg)), 699 error(E, context(prolog_stack(Stack),Msg)), 700 Fr, GuardSpec, Debug) :- 701 current_prolog_flag(backtrace, true), 702 \+ is_stack(Ctx0, _Frames), 703 ( atom(GuardSpec) 704 -> debug(backtrace, 'Got uncaught (guard = ~q) exception ~p (Ctx0=~p)', 705 [GuardSpec, E, Ctx0]), 706 stack_guard(GuardSpec), 707 Guard = GuardSpec 708 ; prolog_frame_attribute(GuardSpec, predicate_indicator, Guard), 709 debug(backtrace, 'Got exception ~p (Ctx0=~p, Catcher=~p)', 710 [E, Ctx0, Guard]), 711 stack_guard(Guard) 712 -> true 713 ; Debug == true, 714 stack_guard(debug), 715 Guard = none 716 ), 717 ( current_prolog_flag(backtrace_depth, Depth) 718 -> Depth > 0 719 ; Depth = 20 % Thread created before lib was loaded 720 ), 721 get_prolog_backtrace(Depth, Stack0, 722 [ frame(Fr), 723 guard(Guard) 724 ]), 725 debug(backtrace, 'Stack = ~p', [Stack0]), 726 clean_stack(Stack0, Stack1), 727 join_stacks(Ctx0, Stack1, Stack). 728 729clean_stack(List, List) :- 730 stack_guard(X), var(X), 731 !. % Do not stop if we catch all 732clean_stack(List, Clean) :- 733 clean_stack2(List, Clean). 734 735clean_stack2([], []). 736clean_stack2([H|_], [H]) :- 737 guard_frame(H), 738 !. 739clean_stack2([H|T0], [H|T]) :- 740 clean_stack2(T0, T). 741 742guard_frame(frame(_,clause(ClauseRef, _, _))) :- 743 nth_clause(M:Head, _, ClauseRef), 744 functor(Head, Name, Arity), 745 stack_guard(M:Name/Arity). 746 747join_stacks(Ctx0, Stack1, Stack) :- 748 nonvar(Ctx0), 749 Ctx0 = prolog_stack(Stack0), 750 is_list(Stack0), !, 751 append(Stack0, Stack1, Stack). 752join_stacks(_, Stack, Stack).
none, 'C' or
the predicate indicator of the guard, the predicate calling
catch/3. The exception must be of compatible with the shape
error(Formal, context(Stack, Msg)). The default is to catch
none, uncaught exceptions. 'C' implies that the callback
from C will handle the exception.764stack_guard(none). 765stack_guard(system:catch_with_backtrace/3). 766stack_guard(debug). 767 768 769 /******************************* 770 * MESSAGES * 771 *******************************/ 772 773:- multifile 774 prolog:message//1. 775 776prologmessage(error(Error, context(Stack, Message))) --> 777 { Message \== 'DWIM could not correct goal', 778 is_stack(Stack, Frames) 779 }, 780 !, 781 '$messages':translate_message(error(Error, context(_, Message))), 782 [ nl, 'In:', nl ], 783 ( {is_list(Frames)} 784 -> message(Frames) 785 ; ['~w'-[Frames]] 786 ). 787 788is_stack(Stack, Frames) :- 789 nonvar(Stack), 790 Stack = prolog_stack(Frames)
Examine the Prolog stack
This module defines high-level primitives for examining the Prolog stack, primarily intended to support debugging. It provides the following functionality:
This library may be enabled by default to improve interactive debugging, for example by adding the lines below to your
<config>/init.plto decorate uncaught exceptions: