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) 2004-2021, 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 ]).
92:- create_prolog_flag(backtrace, true, [type(boolean), keep(true)]). 93:- create_prolog_flag(backtrace_depth, 20, [type(integer), keep(true)]). 94:- create_prolog_flag(backtrace_goal_depth, 3, [type(integer), keep(true)]). 95:- 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.128get_prolog_backtrace(MaxDepth, Stack) :- 129 get_prolog_backtrace(MaxDepth, Stack, []). 130 131get_prolog_backtrace(Fr, MaxDepth, Stack) :- 132 integer(Fr), integer(MaxDepth), var(Stack), 133 !, 134 get_prolog_backtrace_lc(MaxDepth, Stack, [frame(Fr)]), 135 nlc. 136get_prolog_backtrace(MaxDepth, Stack, Options) :- 137 get_prolog_backtrace_lc(MaxDepth, Stack, Options), 138 nlc. % avoid last-call-optimization, such that 139 % the top of the stack is always a nice Prolog 140 % frame 141 142nlc. 143 144get_prolog_backtrace_lc(MaxDepth, Stack, Options) :- 145 ( option(frame(Fr), Options) 146 -> PC = call 147 ; prolog_current_frame(Fr0), 148 prolog_frame_attribute(Fr0, pc, PC), 149 prolog_frame_attribute(Fr0, parent, Fr) 150 ), 151 ( option(goal_term_depth(GoalDepth), Options) 152 -> true 153 ; current_prolog_flag(backtrace_goal_depth, GoalDepth) 154 ), 155 option(guard(Guard), Options, none), 156 ( def_no_clause_refs(Guard) 157 -> DefClauseRefs = false 158 ; DefClauseRefs = true 159 ), 160 option(clause_references(ClauseRefs), Options, DefClauseRefs), 161 must_be(nonneg, GoalDepth), 162 backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, Stack, Options). 163 164def_no_clause_refs(system:catch_with_backtrace/3). 165 166backtrace(0, _, _, _, _, _, [], _) :- !. 167backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, 168 [frame(Level, Where, Goal)|Stack], Options) :- 169 prolog_frame_attribute(Fr, level, Level), 170 ( PC == foreign 171 -> prolog_frame_attribute(Fr, predicate_indicator, Pred), 172 Where = foreign(Pred) 173 ; PC == call 174 -> prolog_frame_attribute(Fr, predicate_indicator, Pred), 175 Where = call(Pred) 176 ; prolog_frame_attribute(Fr, clause, Clause) 177 -> clause_where(ClauseRefs, Clause, PC, Where, Options) 178 ; Where = meta_call 179 ), 180 ( Where == meta_call 181 -> Goal = 0 182 ; copy_goal(GoalDepth, Fr, Goal) 183 ), 184 ( prolog_frame_attribute(Fr, pc, PC2) 185 -> true 186 ; PC2 = foreign 187 ), 188 ( prolog_frame_attribute(Fr, parent, Parent), 189 prolog_frame_attribute(Parent, predicate_indicator, PI), 190 PI == Guard % last frame 191 -> backtrace(1, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) 192 ; prolog_frame_attribute(Fr, parent, Parent), 193 more_stack(Parent) 194 -> D2 is MaxDepth - 1, 195 backtrace(D2, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) 196 ; Stack = [] 197 ). 198 199more_stack(Parent) :- 200 prolog_frame_attribute(Parent, predicate_indicator, PI), 201 \+ ( PI = ('$toplevel':G), 202 G \== (toplevel_call/1) 203 ), 204 !. 205more_stack(_) :- 206 current_prolog_flag(break_level, Break), 207 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.220clause_where(true, Clause, PC, clause(Clause, PC), _). 221clause_where(false, Clause, PC, pred_line(PredName, File:Line), Options) :- 222 option(subgoal_positions(true), Options, true), 223 subgoal_position(Clause, PC, File, CharA, _CharZ), 224 File \= @(_), % XPCE Object reference 225 lineno(File, CharA, Line), 226 clause_predicate_name(Clause, PredName), 227 !. 228clause_where(false, Clause, _PC, pred_line(PredName, File:Line), _Options) :- 229 clause_property(Clause, file(File)), 230 clause_property(Clause, line_count(Line)), 231 clause_predicate_name(Clause, PredName), 232 !. 233clause_where(false, Clause, _PC, clause_name(ClauseName), _Options) :- 234 clause_name(Clause, ClauseName).
name(A1, ..., A16, <skipped Skipped of Arity>, An)
246copy_goal(0, _, 0) :- !. % 0 is not a valid goal 247copy_goal(D, Fr, Goal) :- 248 prolog_frame_attribute(Fr, goal, Goal0), 249 ( Goal0 = Module:Goal1 250 -> copy_term_limit(D, Goal1, Goal2), 251 ( hidden_module(Module) 252 -> Goal = Goal2 253 ; Goal = Module:Goal2 254 ) 255 ; copy_term_limit(D, Goal0, Goal) 256 ). 257 (system). 259hidden_module(user). 260 261copy_term_limit(0, In, '...') :- 262 compound(In), 263 !. 264copy_term_limit(N, In, Out) :- 265 is_dict(In), 266 !, 267 dict_pairs(In, Tag, PairsIn), 268 N2 is N - 1, 269 MaxArity = 16, 270 copy_pairs(PairsIn, N2, MaxArity, PairsOut), 271 dict_pairs(Out, Tag, PairsOut). 272copy_term_limit(N, In, Out) :- 273 compound(In), 274 !, 275 compound_name_arity(In, Functor, Arity), 276 N2 is N - 1, 277 MaxArity = 16, 278 ( Arity =< MaxArity 279 -> compound_name_arity(Out, Functor, Arity), 280 copy_term_args(0, Arity, N2, In, Out) 281 ; OutArity is MaxArity+2, 282 compound_name_arity(Out, Functor, OutArity), 283 copy_term_args(0, MaxArity, N2, In, Out), 284 SkipArg is MaxArity+1, 285 Skipped is Arity - MaxArity - 1, 286 format(atom(Msg), '<skipped ~D of ~D>', [Skipped, Arity]), 287 arg(SkipArg, Out, Msg), 288 arg(Arity, In, InA), 289 arg(OutArity, Out, OutA), 290 copy_term_limit(N2, InA, OutA) 291 ). 292copy_term_limit(_, In, Out) :- 293 copy_term_nat(In, Out). 294 295copy_term_args(I, Arity, Depth, In, Out) :- 296 I < Arity, 297 !, 298 I2 is I + 1, 299 arg(I2, In, InA), 300 arg(I2, Out, OutA), 301 copy_term_limit(Depth, InA, OutA), 302 copy_term_args(I2, Arity, Depth, In, Out). 303copy_term_args(_, _, _, _, _). 304 305copy_pairs([], _, _, []) :- !. 306copy_pairs(Pairs, _, 0, ['<skipped>'-Skipped]) :- 307 !, 308 length(Pairs, Skipped). 309copy_pairs([K-V0|T0], N, MaxArity, [K-V|T]) :- 310 copy_term_limit(N, V0, V), 311 MaxArity1 is MaxArity - 1, 312 copy_pairs(T0, N, MaxArity1, T).
level(Level)predicate(PI)location(File:Line)325prolog_stack_frame_property(frame(Level,_,_), level(Level)). 326prolog_stack_frame_property(frame(_,Where,_), predicate(PI)) :- 327 frame_predicate(Where, PI). 328prolog_stack_frame_property(frame(_,clause(Clause,PC),_), location(File:Line)) :- 329 subgoal_position(Clause, PC, File, CharA, _CharZ), 330 File \= @(_), % XPCE Object reference 331 lineno(File, CharA, Line). 332prolog_stack_frame_property(frame(_,_,_,Goal), goal(Goal)) :- 333 Goal \== 0. 334 335 336frame_predicate(foreign(PI), PI). 337frame_predicate(call(PI), PI). 338frame_predicate(clause(Clause, _PC), PI) :- 339 clause_property(Clause, predicate(PI)). 340 341default_backtrace_options(Options) :- 342 ( current_prolog_flag(backtrace_show_lines, true), 343 current_prolog_flag(iso, false) 344 -> Options = [] 345 ; Options = [subgoal_positions(false)] 346 ).
true, print subgoal line numbers. The default depends
on the Prolog flag backtrace_show_lines.360print_prolog_backtrace(Stream, Backtrace) :- 361 print_prolog_backtrace(Stream, Backtrace, []). 362 363print_prolog_backtrace(Stream, Backtrace, Options) :- 364 default_backtrace_options(DefOptions), 365 merge_options(Options, DefOptions, FinalOptions), 366 phrase(message(Backtrace, FinalOptions), Lines), 367 print_message_lines(Stream, '', Lines). 368 369:- public % Called from some handlers 370 message//1. 371 372message(Backtrace) --> 373 {default_backtrace_options(Options)}, 374 message(Backtrace, Options). 375 376message(Backtrace, Options) --> 377 message_frames(Backtrace, Options), 378 warn_nodebug(Backtrace). 379 380message_frames([], _) --> 381 []. 382message_frames([H|T], Options) --> 383 message_frames(H, Options), 384 ( {T == []} 385 -> [] 386 ; [nl], 387 message_frames(T, Options) 388 ). 389 390message_frames(frame(Level, Where, 0), Options) --> 391 !, 392 level(Level), 393 where_no_goal(Where, Options). 394message_frames(frame(Level, _Where, '$toplevel':toplevel_call(_)), _) --> 395 !, 396 level(Level), 397 [ '<user>'-[] ]. 398message_frames(frame(Level, Where, Goal), Options) --> 399 level(Level), 400 [ ansi(code, '~p', [Goal]) ], 401 where_goal(Where, Options). 402 403where_no_goal(foreign(PI), _) --> 404 [ '~w <foreign>'-[PI] ]. 405where_no_goal(call(PI), _) --> 406 [ '~w'-[PI] ]. 407where_no_goal(pred_line(PredName, File:Line), _) --> 408 !, 409 [ '~w at '-[PredName], url(File:Line) ]. 410where_no_goal(clause_name(ClauseName), _) --> 411 !, 412 [ '~w <no source>'-[ClauseName] ]. 413where_no_goal(clause(Clause, PC), Options) --> 414 { nonvar(Clause), 415 !, 416 clause_where(false, Clause, PC, Where, Options) 417 }, 418 where_no_goal(Where, Options). 419where_no_goal(meta_call, _) --> 420 [ '<meta call>' ]. 421 422where_goal(foreign(_), _) --> 423 [ ' <foreign>'-[] ], 424 !. 425where_goal(pred_line(_PredName, File:Line), _) --> 426 !, 427 [ ' at ', url(File:Line) ]. 428where_goal(clause_name(ClauseName), _) --> 429 !, 430 [ '~w <no source>'-[ClauseName] ]. 431where_goal(clause(Clause, PC), Options) --> 432 { nonvar(Clause), 433 !, 434 clause_where(false, Clause, PC, Where, Options) 435 }, 436 where_goal(Where, Options). 437where_goal(clause(Clause, _PC), _) --> 438 { clause_property(Clause, file(File)), 439 clause_property(Clause, line_count(Line)) 440 }, 441 !, 442 [ ' at ', url(File:Line) ]. 443where_goal(clause(Clause, _PC), _) --> 444 { clause_name(Clause, ClauseName) 445 }, 446 !, 447 [ ' ~w <no source>'-[ClauseName] ]. 448where_goal(_, _) --> 449 []. 450 451level(Level) --> 452 [ '~|~t[~D]~6+ '-[Level] ]. 453 454warn_nodebug(Backtrace) --> 455 { contiguous(Backtrace) }, 456 !. 457warn_nodebug(_Backtrace) --> 458 [ nl,nl, 459 'Note: some frames are missing due to last-call optimization.'-[], nl, 460 'Re-run your program in debug mode (:- debug.) to get more detail.'-[] 461 ]. 462 463contiguous([frame(D0,_,_)|Frames]) :- 464 contiguous(Frames, D0). 465 466contiguous([], _). 467contiguous([frame(D1,_,_)|Frames], D0) :- 468 D1 =:= D0-1, 469 contiguous(Frames, D1).
477:- multifile 478 user:prolog_clause_name/2. 479 480clause_predicate_name(Clause, PredName) :- 481 user:prolog_clause_name(Clause, PredName), 482 !. 483clause_predicate_name(Clause, PredName) :- 484 nth_clause(Head, _N, Clause), 485 !, 486 predicate_name(user:Head, PredName).
493backtrace(MaxDepth) :- 494 get_prolog_backtrace_lc(MaxDepth, Stack, []), 495 print_prolog_backtrace(user_error, Stack). 496 497 498subgoal_position(ClauseRef, PC, File, CharA, CharZ) :- 499 debug(backtrace, 'Term-position in ~p at PC=~w:', [ClauseRef, PC]), 500 clause_info(ClauseRef, File, TPos, _), 501 '$clause_term_position'(ClauseRef, PC, List), 502 debug(backtrace, '\t~p~n', [List]), 503 find_subgoal(List, TPos, PosTerm), 504 compound(PosTerm), 505 arg(1, PosTerm, CharA), 506 arg(2, PosTerm, CharZ).
512find_subgoal(_, Pos, Pos) :- 513 var(Pos), 514 !. 515find_subgoal([A|T], term_position(_, _, _, _, PosL), SPos) :- 516 nth1(A, PosL, Pos), 517 !, 518 find_subgoal(T, Pos, SPos). 519find_subgoal([1|T], brace_term_position(_,_,Pos), SPos) :- 520 !, 521 find_subgoal(T, Pos, SPos). 522find_subgoal(List, parentheses_term_position(_,_,Pos), SPos) :- 523 !, 524 find_subgoal(List, Pos, SPos). 525find_subgoal(_, Pos, Pos).
534lineno(File, Char, Line) :- 535 setup_call_cleanup( 536 ( prolog_clause:try_open_source(File, Fd), 537 set_stream(Fd, newline(detect)) 538 ), 539 lineno_(Fd, Char, Line), 540 close(Fd)). 541 542lineno_(Fd, Char, L) :- 543 stream_property(Fd, position(Pos)), 544 stream_position_data(char_count, Pos, C), 545 C > Char, 546 !, 547 stream_position_data(line_count, Pos, L0), 548 L is L0-1. 549lineno_(Fd, Char, L) :- 550 skip(Fd, 0'\n), 551 lineno_(Fd, Char, L). 552 553 554 /******************************* 555 * CHOICEPOINTS * 556 *******************************/
562print_last_choicepoint :- 563 prolog_current_choice(ChI0), % Choice in print_last_choicepoint/0 564 prolog_choice_attribute(ChI0, parent, ChI1), 565 print_last_choicepoint(ChI1, []). 566print_last_choicepoint.
570print_last_choicepoint(ChI1, Options) :- 571 real_choice(ChI1, ChI), 572 prolog_choice_attribute(ChI, frame, F), 573 prolog_frame_attribute(F, goal, Goal), 574 Goal \= '$execute_goal2'(_,_,_), % Toplevel REPL choicepoint 575 !, 576 option(message_level(Level), Options, warning), 577 get_prolog_backtrace(2, [_|Stack], [frame(F)]), 578 ( predicate_property(Goal, foreign) 579 -> print_message(Level, choicepoint(foreign(Goal), Stack)) 580 ; prolog_frame_attribute(F, clause, Clause), 581 ( prolog_choice_attribute(ChI, pc, PC) 582 -> Ctx = jump(PC) 583 ; prolog_choice_attribute(ChI, clause, Next) 584 -> Ctx = clause(Next) 585 ), 586 print_message(Level, choicepoint(clause(Goal, Clause, Ctx), Stack)) 587 ). 588print_last_choicepoint(_, _). 589 590real_choice(Ch0, Ch) :- 591 prolog_choice_attribute(Ch0, type, Type), 592 dummy_type(Type), 593 !, 594 prolog_choice_attribute(Ch0, parent, Ch1), 595 real_choice(Ch1, Ch). 596real_choice(Ch, Ch). 597 598dummy_type(debug). 599dummy_type(none). 600 601prologmessage(choicepoint(Choice, Stack)) --> 602 choice(Choice), 603 [ nl, 'Called from', nl ], 604 message(Stack). 605 606choice(foreign(Goal)) --> 607 success_goal(Goal, 'a foreign choice point'). 608choice(clause(Goal, ClauseRef, clause(Next))) --> 609 success_goal(Goal, 'a choice point in alternate clause'), 610 [ nl ], 611 [ ' ' ], clause_descr(ClauseRef), [': clause succeeded', nl], 612 [ ' ' ], clause_descr(Next), [': next candidate clause' ]. 613choice(clause(Goal, ClauseRef, jump(PC))) --> 614 { clause_where(false, ClauseRef, PC, Where, 615 [subgoal_positions(true)]) 616 }, 617 success_goal(Goal, 'an in-clause choice point'), 618 [ nl, ' ' ], 619 where_no_goal(Where). 620 621success_goal(Goal, Reason) --> 622 [ ansi(code, '~p', [Goal]), 623 ' left ~w (after success)'-[Reason] 624 ]. 625 626where_no_goal(pred_line(_PredName, File:Line)) --> 627 !, 628 [ url(File:Line) ]. 629where_no_goal(clause_name(ClauseName)) --> 630 !, 631 [ '~w <no source>'-[ClauseName] ]. 632 633clause_descr(ClauseRef) --> 634 { clause_property(ClauseRef, file(File)), 635 clause_property(ClauseRef, line_count(Line)) 636 }, 637 !, 638 [ url(File:Line) ]. 639clause_descr(ClauseRef) --> 640 { clause_name(ClauseRef, Name) 641 }, 642 [ '~w'-[Name] ]. 643 644 645 /******************************* 646 * DECORATE ERRORS * 647 *******************************/
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.683:- multifile prolog:prolog_exception_hook/5. 684:- dynamic prolog:prolog_exception_hook/5. 685 686prolog:prolog_exception_hook(error(E, context(Ctx0,Msg)), 687 error(E, context(prolog_stack(Stack),Msg)), 688 Fr, GuardSpec, Debug) :- 689 current_prolog_flag(backtrace, true), 690 \+ is_stack(Ctx0, _Frames), 691 ( atom(GuardSpec) 692 -> debug(backtrace, 'Got uncaught (guard = ~q) exception ~p (Ctx0=~p)', 693 [GuardSpec, E, Ctx0]), 694 stack_guard(GuardSpec), 695 Guard = GuardSpec 696 ; prolog_frame_attribute(GuardSpec, predicate_indicator, Guard), 697 debug(backtrace, 'Got exception ~p (Ctx0=~p, Catcher=~p)', 698 [E, Ctx0, Guard]), 699 stack_guard(Guard) 700 -> true 701 ; Debug == true, 702 stack_guard(debug), 703 Guard = none 704 ), 705 ( current_prolog_flag(backtrace_depth, Depth) 706 -> Depth > 0 707 ; Depth = 20 % Thread created before lib was loaded 708 ), 709 get_prolog_backtrace(Depth, Stack0, 710 [ frame(Fr), 711 guard(Guard) 712 ]), 713 debug(backtrace, 'Stack = ~p', [Stack0]), 714 clean_stack(Stack0, Stack1), 715 join_stacks(Ctx0, Stack1, Stack). 716 717clean_stack(List, List) :- 718 stack_guard(X), var(X), 719 !. % Do not stop if we catch all 720clean_stack(List, Clean) :- 721 clean_stack2(List, Clean). 722 723clean_stack2([], []). 724clean_stack2([H|_], [H]) :- 725 guard_frame(H), 726 !. 727clean_stack2([H|T0], [H|T]) :- 728 clean_stack2(T0, T). 729 730guard_frame(frame(_,clause(ClauseRef, _, _))) :- 731 nth_clause(M:Head, _, ClauseRef), 732 functor(Head, Name, Arity), 733 stack_guard(M:Name/Arity). 734 735join_stacks(Ctx0, Stack1, Stack) :- 736 nonvar(Ctx0), 737 Ctx0 = prolog_stack(Stack0), 738 is_list(Stack0), !, 739 append(Stack0, Stack1, Stack). 740join_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.752stack_guard(none). 753stack_guard(system:catch_with_backtrace/3). 754stack_guard(debug). 755 756 757 /******************************* 758 * MESSAGES * 759 *******************************/ 760 761:- multifile 762 prolog:message//1. 763 764prologmessage(error(Error, context(Stack, Message))) --> 765 { Message \== 'DWIM could not correct goal', 766 is_stack(Stack, Frames) 767 }, 768 !, 769 '$messages':translate_message(error(Error, context(_, Message))), 770 [ nl, 'In:', nl ], 771 ( {is_list(Frames)} 772 -> message(Frames) 773 ; ['~w'-[Frames]] 774 ). 775 776is_stack(Stack, Frames) :- 777 nonvar(Stack), 778 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: