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:- autoload(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, PI). 340 341default_backtrace_options(Options) :- 342 ( current_prolog_flag(backtrace_show_lines, true) 343 -> Options = [] 344 ; Options = [subgoal_positions(false)] 345 ).
true, print subgoal line numbers. The default depends
on the Prolog flag backtrace_show_lines.359print_prolog_backtrace(Stream, Backtrace) :- 360 print_prolog_backtrace(Stream, Backtrace, []). 361 362print_prolog_backtrace(Stream, Backtrace, Options) :- 363 default_backtrace_options(DefOptions), 364 merge_options(Options, DefOptions, FinalOptions), 365 phrase(message(Backtrace, FinalOptions), Lines), 366 print_message_lines(Stream, '', Lines). 367 368:- public % Called from some handlers 369 message//1. 370 371message(Backtrace) --> 372 {default_backtrace_options(Options)}, 373 message(Backtrace, Options). 374 375message(Backtrace, Options) --> 376 message_frames(Backtrace, Options), 377 warn_nodebug(Backtrace). 378 379message_frames([], _) --> 380 []. 381message_frames([H|T], Options) --> 382 message_frames(H, Options), 383 ( {T == []} 384 -> [] 385 ; [nl], 386 message_frames(T, Options) 387 ). 388 389message_frames(frame(Level, Where, 0), Options) --> 390 !, 391 level(Level), 392 where_no_goal(Where, Options). 393message_frames(frame(Level, _Where, '$toplevel':toplevel_call(_)), _) --> 394 !, 395 level(Level), 396 [ '<user>'-[] ]. 397message_frames(frame(Level, Where, Goal), Options) --> 398 level(Level), 399 [ ansi(code, '~p', [Goal]) ], 400 where_goal(Where, Options). 401 402where_no_goal(foreign(PI), _) --> 403 [ '~w <foreign>'-[PI] ]. 404where_no_goal(call(PI), _) --> 405 [ '~w'-[PI] ]. 406where_no_goal(pred_line(PredName, File:Line), _) --> 407 !, 408 [ '~w at '-[PredName], url(File:Line) ]. 409where_no_goal(clause_name(ClauseName), _) --> 410 !, 411 [ '~w <no source>'-[ClauseName] ]. 412where_no_goal(clause(Clause, PC), Options) --> 413 { nonvar(Clause), 414 !, 415 clause_where(false, Clause, PC, Where, Options) 416 }, 417 where_no_goal(Where, Options). 418where_no_goal(meta_call, _) --> 419 [ '<meta call>' ]. 420 421where_goal(foreign(_), _) --> 422 [ ' <foreign>'-[] ], 423 !. 424where_goal(pred_line(_PredName, File:Line), _) --> 425 !, 426 [ ' at ', url(File:Line) ]. 427where_goal(clause_name(ClauseName), _) --> 428 !, 429 [ '~w <no source>'-[ClauseName] ]. 430where_goal(clause(Clause, PC), Options) --> 431 { nonvar(Clause), 432 !, 433 clause_where(false, Clause, PC, Where, Options) 434 }, 435 where_goal(Where, Options). 436where_goal(clause(Clause, _PC), _) --> 437 { clause_property(Clause, file(File)), 438 clause_property(Clause, line_count(Line)) 439 }, 440 !, 441 [ ' at ', url(File:Line) ]. 442where_goal(clause(Clause, _PC), _) --> 443 { clause_name(Clause, ClauseName) 444 }, 445 !, 446 [ ' ~w <no source>'-[ClauseName] ]. 447where_goal(_, _) --> 448 []. 449 450level(Level) --> 451 [ '~|~t[~D]~6+ '-[Level] ]. 452 453warn_nodebug(Backtrace) --> 454 { contiguous(Backtrace) }, 455 !. 456warn_nodebug(_Backtrace) --> 457 [ nl,nl, 458 'Note: some frames are missing due to last-call optimization.'-[], nl, 459 'Re-run your program in debug mode (:- debug.) to get more detail.'-[] 460 ]. 461 462contiguous([frame(D0,_,_)|Frames]) :- 463 contiguous(Frames, D0). 464 465contiguous([], _). 466contiguous([frame(D1,_,_)|Frames], D0) :- 467 D1 =:= D0-1, 468 contiguous(Frames, D1).
476clause_predicate_name(Clause, PredName) :- 477 user:prolog_clause_name(Clause, PredName), 478 !. 479clause_predicate_name(Clause, PredName) :- 480 nth_clause(Head, _N, Clause), 481 !, 482 predicate_name(user:Head, PredName).
489backtrace(MaxDepth) :- 490 get_prolog_backtrace_lc(MaxDepth, Stack, []), 491 print_prolog_backtrace(user_error, Stack). 492 493 494subgoal_position(ClauseRef, PC, File, CharA, CharZ) :- 495 debug(backtrace, 'Term-position in ~p at PC=~w:', [ClauseRef, PC]), 496 clause_info(ClauseRef, File, TPos, _), 497 '$clause_term_position'(ClauseRef, PC, List), 498 debug(backtrace, '\t~p~n', [List]), 499 find_subgoal(List, TPos, PosTerm), 500 arg(1, PosTerm, CharA), 501 arg(2, PosTerm, CharZ).
507find_subgoal(_, Pos, Pos) :- 508 var(Pos), 509 !. 510find_subgoal([A|T], term_position(_, _, _, _, PosL), SPos) :- 511 nth1(A, PosL, Pos), 512 !, 513 find_subgoal(T, Pos, SPos). 514find_subgoal([1|T], brace_term_position(_,_,Pos), SPos) :- 515 !, 516 find_subgoal(T, Pos, SPos). 517find_subgoal(List, parentheses_term_position(_,_,Pos), SPos) :- 518 !, 519 find_subgoal(List, Pos, SPos). 520find_subgoal(_, Pos, Pos).
529lineno(File, Char, Line) :- 530 setup_call_cleanup( 531 ( prolog_clause:try_open_source(File, Fd), 532 set_stream(Fd, newline(detect)) 533 ), 534 lineno_(Fd, Char, Line), 535 close(Fd)). 536 537lineno_(Fd, Char, L) :- 538 stream_property(Fd, position(Pos)), 539 stream_position_data(char_count, Pos, C), 540 C > Char, 541 !, 542 stream_position_data(line_count, Pos, L0), 543 L is L0-1. 544lineno_(Fd, Char, L) :- 545 skip(Fd, 0'\n), 546 lineno_(Fd, Char, L). 547 548 549 /******************************* 550 * CHOICEPOINTS * 551 *******************************/
557print_last_choicepoint :- 558 prolog_current_choice(ChI0), % Choice in print_last_choicepoint/0 559 prolog_choice_attribute(ChI0, parent, ChI1), 560 print_last_choicepoint(ChI1, []). 561print_last_choicepoint.
565print_last_choicepoint(ChI1, Options) :- 566 real_choice(ChI1, ChI), 567 prolog_choice_attribute(ChI, frame, F), 568 prolog_frame_attribute(F, goal, Goal), 569 Goal \= '$execute_goal2'(_,_,_), % Toplevel REPL choicepoint 570 !, 571 option(message_level(Level), Options, warning), 572 get_prolog_backtrace(2, [_|Stack], [frame(F)]), 573 ( predicate_property(Goal, foreign) 574 -> print_message(Level, choicepoint(foreign(Goal), Stack)) 575 ; prolog_frame_attribute(F, clause, Clause), 576 ( prolog_choice_attribute(ChI, pc, PC) 577 -> Ctx = jump(PC) 578 ; prolog_choice_attribute(ChI, clause, Next) 579 -> Ctx = clause(Next) 580 ), 581 print_message(Level, choicepoint(clause(Goal, Clause, Ctx), Stack)) 582 ). 583print_last_choicepoint(_, _). 584 585real_choice(Ch0, Ch) :- 586 prolog_choice_attribute(Ch0, type, Type), 587 dummy_type(Type), 588 !, 589 prolog_choice_attribute(Ch0, parent, Ch1), 590 real_choice(Ch1, Ch). 591real_choice(Ch, Ch). 592 593dummy_type(debug). 594dummy_type(none). 595 596prologmessage(choicepoint(Choice, Stack)) --> 597 choice(Choice), 598 [ nl, 'Called from', nl ], 599 message(Stack). 600 601choice(foreign(Goal)) --> 602 success_goal(Goal, 'a foreign choice point'). 603choice(clause(Goal, ClauseRef, clause(Next))) --> 604 success_goal(Goal, 'a choice point in alternate clause'), 605 [ nl ], 606 [ ' ' ], clause_descr(ClauseRef), [': clause succeeded', nl], 607 [ ' ' ], clause_descr(Next), [': next candidate clause' ]. 608choice(clause(Goal, ClauseRef, jump(PC))) --> 609 { clause_where(false, ClauseRef, PC, Where, 610 [subgoal_positions(true)]) 611 }, 612 success_goal(Goal, 'an in-clause choice point'), 613 [ nl, ' ' ], 614 where_no_goal(Where). 615 616success_goal(Goal, Reason) --> 617 [ ansi(code, '~p', [Goal]), 618 ' left ~w (after success)'-[Reason] 619 ]. 620 621where_no_goal(pred_line(_PredName, File:Line)) --> 622 !, 623 [ url(File:Line) ]. 624where_no_goal(clause_name(ClauseName)) --> 625 !, 626 [ '~w <no source>'-[ClauseName] ]. 627 628clause_descr(ClauseRef) --> 629 { clause_property(ClauseRef, file(File)), 630 clause_property(ClauseRef, line_count(Line)) 631 }, 632 !, 633 [ url(File:Line) ]. 634clause_descr(ClauseRef) --> 635 { clause_name(ClauseRef, Name) 636 }, 637 [ '~w'-[Name] ]. 638 639 640 /******************************* 641 * DECORATE ERRORS * 642 *******************************/
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.678:- multifile 679 user:prolog_exception_hook/4. 680:- dynamic 681 user:prolog_exception_hook/4. 682 683user:prolog_exception_hook(error(E, context(Ctx0,Msg)), 684 error(E, context(prolog_stack(Stack),Msg)), 685 Fr, GuardSpec) :- 686 current_prolog_flag(backtrace, true), 687 \+ is_stack(Ctx0, _Frames), 688 ( atom(GuardSpec) 689 -> debug(backtrace, 'Got uncaught (guard = ~q) exception ~p (Ctx0=~p)', 690 [GuardSpec, E, Ctx0]), 691 stack_guard(GuardSpec), 692 Guard = GuardSpec 693 ; prolog_frame_attribute(GuardSpec, predicate_indicator, Guard), 694 debug(backtrace, 'Got exception ~p (Ctx0=~p, Catcher=~p)', 695 [E, Ctx0, Guard]), 696 stack_guard(Guard) 697 ), 698 ( current_prolog_flag(backtrace_depth, Depth) 699 -> Depth > 0 700 ; Depth = 20 % Thread created before lib was loaded 701 ), 702 get_prolog_backtrace(Depth, Stack0, 703 [ frame(Fr), 704 guard(Guard) 705 ]), 706 debug(backtrace, 'Stack = ~p', [Stack0]), 707 clean_stack(Stack0, Stack1), 708 join_stacks(Ctx0, Stack1, Stack). 709 710clean_stack(List, List) :- 711 stack_guard(X), var(X), 712 !. % Do not stop if we catch all 713clean_stack(List, Clean) :- 714 clean_stack2(List, Clean). 715 716clean_stack2([], []). 717clean_stack2([H|_], [H]) :- 718 guard_frame(H), 719 !. 720clean_stack2([H|T0], [H|T]) :- 721 clean_stack2(T0, T). 722 723guard_frame(frame(_,clause(ClauseRef, _, _))) :- 724 nth_clause(M:Head, _, ClauseRef), 725 functor(Head, Name, Arity), 726 stack_guard(M:Name/Arity). 727 728join_stacks(Ctx0, Stack1, Stack) :- 729 nonvar(Ctx0), 730 Ctx0 = prolog_stack(Stack0), 731 is_list(Stack0), !, 732 append(Stack0, Stack1, Stack). 733join_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.745stack_guard(none). 746stack_guard(system:catch_with_backtrace/3). 747 748 749 /******************************* 750 * MESSAGES * 751 *******************************/ 752 753:- multifile 754 prolog:message//1. 755 756prologmessage(error(Error, context(Stack, Message))) --> 757 { Message \== 'DWIM could not correct goal', 758 is_stack(Stack, Frames) 759 }, 760 !, 761 '$messages':translate_message(error(Error, context(_, Message))), 762 [ nl, 'In:', nl ], 763 ( {is_list(Frames)} 764 -> message(Frames) 765 ; ['~w'-[Frames]] 766 ). 767 768is_stack(Stack, Frames) :- 769 nonvar(Stack), 770 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: