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).
330prolog_stack_frame_property(frame(Level,_,_), level(Level)). 331prolog_stack_frame_property(frame(_,Where,_), predicate(PI)) :- 332 frame_predicate(Where, PI). 333prolog_stack_frame_property(frame(_,clause(Clause,PC),_), location(File:Line)) :- 334 subgoal_position(Clause, PC, File, CharA, _CharZ), 335 File \= @(_), % XPCE Object reference 336 lineno(File, CharA, Line). 337prolog_stack_frame_property(frame(_,_,_,Goal), goal(Goal)) :- 338 Goal \== 0. 339 340 341frame_predicate(foreign(PI), PI). 342frame_predicate(call(PI), PI). 343frame_predicate(clause(Clause, _PC), PI) :- 344 clause_property(Clause, predicate(PI)). 345 346default_backtrace_options(Options) :- 347 ( current_prolog_flag(backtrace_show_lines, true), 348 current_prolog_flag(iso, false) 349 -> Options = [] 350 ; Options = [subgoal_positions(false)] 351 ).
true. print subgoal line numbers. The default depends
on the Prolog flag backtrace_show_lines.absolute or
basename.368print_prolog_backtrace(Stream, Backtrace) :- 369 print_prolog_backtrace(Stream, Backtrace, []). 370 371print_prolog_backtrace(Stream, Backtrace, Options) :- 372 default_backtrace_options(DefOptions), 373 merge_options(Options, DefOptions, FinalOptions), 374 phrase(message(Backtrace, FinalOptions), Lines), 375 print_message_lines(Stream, '', Lines). 376 377:- public % Called from some handlers 378 message//1. 379 380message(Backtrace) --> 381 {default_backtrace_options(Options)}, 382 message(Backtrace, Options). 383 384message(Backtrace, Options) --> 385 message_frames(Backtrace, Options), 386 warn_nodebug(Backtrace). 387 388message_frames([], _) --> 389 []. 390message_frames([H|T], Options) --> 391 message_frames(H, Options), 392 ( {T == []} 393 -> [] 394 ; [nl], 395 message_frames(T, Options) 396 ). 397 398message_frames(frame(Level, Where, 0), Options) --> 399 !, 400 level(Level), 401 where_no_goal(Where, Options). 402message_frames(frame(Level, _Where, '$toplevel':toplevel_call(_)), _) --> 403 !, 404 level(Level), 405 [ '<user>'-[] ]. 406message_frames(frame(Level, Where, Goal), Options) --> 407 level(Level), 408 [ ansi(code, '~p', [Goal]) ], 409 where_goal(Where, Options). 410 411where_no_goal(foreign(PI), _) --> 412 [ '~w <foreign>'-[PI] ]. 413where_no_goal(call(PI), _) --> 414 [ '~w'-[PI] ]. 415where_no_goal(pred_line(PredName, File:Line), Options) --> 416 !, 417 [ '~w at '-[PredName] ], file_line(File:Line, Options). 418where_no_goal(clause_name(ClauseName), _) --> 419 !, 420 [ '~w <no source>'-[ClauseName] ]. 421where_no_goal(clause(Clause, PC), Options) --> 422 { nonvar(Clause), 423 !, 424 clause_where(false, Clause, PC, Where, Options) 425 }, 426 where_no_goal(Where, Options). 427where_no_goal(meta_call, _) --> 428 [ '<meta call>' ]. 429 430where_goal(foreign(_), _) --> 431 [ ' <foreign>'-[] ], 432 !. 433where_goal(pred_line(_PredName, File:Line), Options) --> 434 !, 435 [ ' at ' ], file_line(File:Line, Options). 436where_goal(clause_name(ClauseName), _) --> 437 !, 438 [ '~w <no source>'-[ClauseName] ]. 439where_goal(clause(Clause, PC), Options) --> 440 { nonvar(Clause), 441 !, 442 clause_where(false, Clause, PC, Where, Options) 443 }, 444 where_goal(Where, Options). 445where_goal(clause(Clause, _PC), _) --> 446 { clause_property(Clause, file(File)), 447 clause_property(Clause, line_count(Line)) 448 }, 449 !, 450 [ ' at ', url(File:Line) ]. 451where_goal(clause(Clause, _PC), _) --> 452 { clause_name(Clause, ClauseName) 453 }, 454 !, 455 [ ' ~w <no source>'-[ClauseName] ]. 456where_goal(_, _) --> 457 []. 458 459level(Level) --> 460 [ ansi(bold, '~|~t[~D]~6+ ', [Level]) ]. 461 462file_line(File:Line, Options), option(show_files(basename), Options) ==> 463 { file_base_name(File, Base), 464 format(string(Label), '~w:~d', [Base, Line]) 465 }, 466 [ url(File:Line, Label) ]. 467file_line(File:Line, _Options) ==> 468 [ url(File:Line) ]. 469 470warn_nodebug(Backtrace) --> 471 { contiguous(Backtrace) }, 472 !. 473warn_nodebug(_Backtrace) --> 474 [ nl,nl, 475 'Note: some frames are missing due to last-call optimization.'-[], nl, 476 'Re-run your program in debug mode (:- debug.) to get more detail.'-[] 477 ]. 478 479contiguous([frame(D0,_,_)|Frames]) :- 480 contiguous(Frames, D0). 481 482contiguous([], _). 483contiguous([frame(D1,_,_)|Frames], D0) :- 484 D1 =:= D0-1, 485 contiguous(Frames, D1).
493:- multifile 494 user:prolog_clause_name/2. 495 496clause_predicate_name(Clause, PredName) :- 497 user:prolog_clause_name(Clause, PredName), 498 !. 499clause_predicate_name(Clause, PredName) :- 500 nth_clause(Head, _N, Clause), 501 !, 502 predicate_name(user:Head, PredName).
509backtrace(MaxDepth) :- 510 get_prolog_backtrace_lc(MaxDepth, Stack, []), 511 print_prolog_backtrace(user_error, Stack). 512 513 514subgoal_position(ClauseRef, PC, File, CharA, CharZ) :- 515 debug(backtrace, 'Term-position in ~p at PC=~w:', [ClauseRef, PC]), 516 clause_info(ClauseRef, File, TPos, _), 517 '$clause_term_position'(ClauseRef, PC, List), 518 debug(backtrace, '\t~p~n', [List]), 519 find_subgoal(List, TPos, PosTerm), 520 compound(PosTerm), 521 arg(1, PosTerm, CharA), 522 arg(2, PosTerm, CharZ).
528find_subgoal(_, Pos, Pos) :- 529 var(Pos), 530 !. 531find_subgoal([A|T], term_position(_, _, _, _, PosL), SPos) :- 532 nth1(A, PosL, Pos), 533 !, 534 find_subgoal(T, Pos, SPos). 535find_subgoal([1|T], brace_term_position(_,_,Pos), SPos) :- 536 !, 537 find_subgoal(T, Pos, SPos). 538find_subgoal(List, parentheses_term_position(_,_,Pos), SPos) :- 539 !, 540 find_subgoal(List, Pos, SPos). 541find_subgoal(_, Pos, Pos).
550lineno(File, Char, Line) :- 551 setup_call_cleanup( 552 ( prolog_clause:try_open_source(File, Fd), 553 set_stream(Fd, newline(detect)) 554 ), 555 lineno_(Fd, Char, Line), 556 close(Fd)). 557 558lineno_(Fd, Char, L) :- 559 stream_property(Fd, position(Pos)), 560 stream_position_data(char_count, Pos, C), 561 C > Char, 562 !, 563 stream_position_data(line_count, Pos, L0), 564 L is L0-1. 565lineno_(Fd, Char, L) :- 566 skip(Fd, 0'\n), 567 lineno_(Fd, Char, L). 568 569 570 /******************************* 571 * CHOICEPOINTS * 572 *******************************/
578print_last_choicepoint :- 579 prolog_current_choice(ChI0), % Choice in print_last_choicepoint/0 580 prolog_choice_attribute(ChI0, parent, ChI1), 581 print_last_choicepoint(ChI1, []). 582print_last_choicepoint.
586print_last_choicepoint(ChI1, Options) :- 587 real_choice(ChI1, ChI), 588 prolog_choice_attribute(ChI, frame, F), 589 prolog_frame_attribute(F, goal, Goal), 590 Goal \= '$execute_goal2'(_,_,_), % Toplevel REPL choicepoint 591 !, 592 option(message_level(Level), Options, warning), 593 get_prolog_backtrace(2, [_|Stack], [frame(F)]), 594 ( predicate_property(Goal, foreign) 595 -> print_message(Level, choicepoint(foreign(Goal), Stack)) 596 ; prolog_frame_attribute(F, clause, Clause), 597 ( prolog_choice_attribute(ChI, pc, PC) 598 -> Ctx = jump(PC) 599 ; prolog_choice_attribute(ChI, clause, Next) 600 -> Ctx = clause(Next) 601 ), 602 print_message(Level, choicepoint(clause(Goal, Clause, Ctx), Stack)) 603 ). 604print_last_choicepoint(_, _). 605 606real_choice(Ch0, Ch) :- 607 prolog_choice_attribute(Ch0, type, Type), 608 dummy_type(Type), 609 !, 610 prolog_choice_attribute(Ch0, parent, Ch1), 611 real_choice(Ch1, Ch). 612real_choice(Ch, Ch). 613 614dummy_type(debug). 615dummy_type(none). 616 617prologmessage(choicepoint(Choice, Stack)) --> 618 choice(Choice), 619 [ nl, 'Called from', nl ], 620 message(Stack). 621 622choice(foreign(Goal)) --> 623 success_goal(Goal, 'a foreign choice point'). 624choice(clause(Goal, ClauseRef, clause(Next))) --> 625 success_goal(Goal, 'a choice point in alternate clause'), 626 [ nl ], 627 [ ' ' ], clause_descr(ClauseRef), [': clause succeeded', nl], 628 [ ' ' ], clause_descr(Next), [': next candidate clause' ]. 629choice(clause(Goal, ClauseRef, jump(PC))) --> 630 { clause_where(false, ClauseRef, PC, Where, 631 [subgoal_positions(true)]) 632 }, 633 success_goal(Goal, 'an in-clause choice point'), 634 [ nl, ' ' ], 635 where_no_goal(Where). 636 637success_goal(Goal, Reason) --> 638 [ ansi(code, '~p', [Goal]), 639 ' left ~w (after success)'-[Reason] 640 ]. 641 642where_no_goal(pred_line(_PredName, File:Line)) --> 643 !, 644 [ url(File:Line) ]. 645where_no_goal(clause_name(ClauseName)) --> 646 !, 647 [ '~w <no source>'-[ClauseName] ]. 648 649clause_descr(ClauseRef) --> 650 { clause_property(ClauseRef, file(File)), 651 clause_property(ClauseRef, line_count(Line)) 652 }, 653 !, 654 [ url(File:Line) ]. 655clause_descr(ClauseRef) --> 656 { clause_name(ClauseRef, Name) 657 }, 658 [ '~w'-[Name] ]. 659 660 661 /******************************* 662 * DECORATE ERRORS * 663 *******************************/
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.699:- multifile prolog:prolog_exception_hook/5. 700:- dynamic prolog:prolog_exception_hook/5. 701 702prolog:prolog_exception_hook(error(E, context(Ctx0,Msg)), 703 error(E, context(prolog_stack(Stack),Msg)), 704 Fr, GuardSpec, Debug) :- 705 current_prolog_flag(backtrace, true), 706 \+ is_stack(Ctx0, _Frames), 707 ( atom(GuardSpec) 708 -> debug(backtrace, 'Got uncaught (guard = ~q) exception ~p (Ctx0=~p)', 709 [GuardSpec, E, Ctx0]), 710 stack_guard(GuardSpec), 711 Guard = GuardSpec 712 ; prolog_frame_attribute(GuardSpec, predicate_indicator, Guard), 713 debug(backtrace, 'Got exception ~p (Ctx0=~p, Catcher=~p)', 714 [E, Ctx0, Guard]), 715 stack_guard(Guard) 716 -> true 717 ; Debug == true, 718 stack_guard(debug), 719 Guard = none 720 ), 721 ( current_prolog_flag(backtrace_depth, Depth) 722 -> Depth > 0 723 ; Depth = 20 % Thread created before lib was loaded 724 ), 725 get_prolog_backtrace(Depth, Stack0, 726 [ frame(Fr), 727 guard(Guard) 728 ]), 729 debug(backtrace, 'Stack = ~p', [Stack0]), 730 clean_stack(Stack0, Stack1), 731 join_stacks(Ctx0, Stack1, Stack). 732 733clean_stack(List, List) :- 734 stack_guard(X), var(X), 735 !. % Do not stop if we catch all 736clean_stack(List, Clean) :- 737 clean_stack2(List, Clean). 738 739clean_stack2([], []). 740clean_stack2([H|_], [H]) :- 741 guard_frame(H), 742 !. 743clean_stack2([H|T0], [H|T]) :- 744 clean_stack2(T0, T). 745 746guard_frame(frame(_,clause(ClauseRef, _, _))) :- 747 nth_clause(M:Head, _, ClauseRef), 748 functor(Head, Name, Arity), 749 stack_guard(M:Name/Arity). 750 751join_stacks(Ctx0, Stack1, Stack) :- 752 nonvar(Ctx0), 753 Ctx0 = prolog_stack(Stack0), 754 is_list(Stack0), !, 755 append(Stack0, Stack1, Stack). 756join_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.768stack_guard(none). 769stack_guard(system:catch_with_backtrace/3). 770stack_guard(debug). 771 772 773 /******************************* 774 * MESSAGES * 775 *******************************/ 776 777:- multifile 778 prolog:message//1. 779 780prologmessage(error(Error, context(Stack, Message))) --> 781 { Message \== 'DWIM could not correct goal', 782 is_stack(Stack, Frames) 783 }, 784 !, 785 '$messages':translate_message(error(Error, context(_, Message))), 786 [ nl, 'In:', nl ], 787 ( {is_list(Frames)} 788 -> message(Frames) 789 ; ['~w'-[Frames]] 790 ). 791 792is_stack(Stack, Frames) :- 793 nonvar(Stack), 794 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: