/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2004-2021, University of Amsterdam VU University Amsterdam SWI-Prolog Solutions b.v. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module(prolog_stack, [ get_prolog_backtrace/2, % +MaxDepth, -Stack get_prolog_backtrace/3, % +MaxDepth, -Stack, +Options prolog_stack_frame_property/2, % +Frame, ?Property print_prolog_backtrace/2, % +Stream, +Stack print_prolog_backtrace/3, % +Stream, +Stack, +Options backtrace/1, % +MaxDepth print_last_choicepoint/0, print_last_choicepoint/2 % +Choice, +Options ]). :- autoload(library(debug),[debug/3]). :- autoload(library(error),[must_be/2]). :- autoload(library(lists),[nth1/3,append/3]). :- autoload(library(option),[option/2,option/3,merge_options/3]). :- autoload(library(prolog_clause), [clause_name/2,predicate_name/2,clause_info/4]). :- dynamic stack_guard/1. :- multifile stack_guard/1. :- predicate_options(print_prolog_backtrace/3, 3, [ subgoal_positions(boolean) ]). /** 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: * get_prolog_backtrace/2 gets a Prolog representation of the Prolog stack. This can be used for printing, but also to enrich exceptions using prolog_exception_hook/4. Decorating exceptions is provided by this library and controlled by the hook stack_guard/1. * print_prolog_backtrace/2 prints a backtrace as returned by get_prolog_backtrace/2 * The shorthand backtrace/1 fetches and prints a backtrace. This library may be enabled by default to improve interactive debugging, for example by adding the lines below to your ``/init.pl`` to decorate uncaught exceptions: == :- use_module(library(prolog_stack)). == @bug Use of this library may negatively impact performance of applications that process (error-)exceptions frequently as part of their normal processing. */ :- create_prolog_flag(backtrace, true, [type(boolean), keep(true)]). :- create_prolog_flag(backtrace_depth, 20, [type(integer), keep(true)]). :- create_prolog_flag(backtrace_goal_depth, 3, [type(integer), keep(true)]). :- create_prolog_flag(backtrace_show_lines, true, [type(boolean), keep(true)]). %! get_prolog_backtrace(+MaxDepth, -Backtrace) is det. %! get_prolog_backtrace(+MaxDepth, -Backtrace, +Options) is det. % % Obtain a backtrace from the current location. The backtrace is a % list of frames. Each frame is an opaque term that can be % inspected using the predicate prolog_stack_frame_property/2 can % be used to extract information from these frames. Most use % scenarios will pass the stack to print_prolog_backtrace/2. The % following options are provided: % % * frame(+Frame) % Start at Frame instead of the current frame. % * goal_term_depth(+Depth) % If Depth > 0, include a shallow copy of the goal arguments % into the stack. Default is set by the Prolog flag % `backtrace_goal_depth`, set to `3` initially, showing the % goal and toplevel of any argument. % * guard(+Guard) % Do not show stack frames above Guard. See stack_guard/1. % * clause_references(+Bool) % Report locations as `Clause+PC` or as a location term that % does not use clause references, allowing the exception to % be printed safely in a different context. % % @param Frame is the frame to start from. See prolog_current_frame/1. % @param MaxDepth defines the maximum number of frames returned. % @compat get_prolog_backtrace/3 used to have the parameters % +Frame, +MaxDepth, -Backtrace. A call that matches this % signature is mapped to get_prolog_backtrace(MaxDepth, Backtrace, % [frame(Frame)]). get_prolog_backtrace(MaxDepth, Stack) :- get_prolog_backtrace(MaxDepth, Stack, []). get_prolog_backtrace(Fr, MaxDepth, Stack) :- integer(Fr), integer(MaxDepth), var(Stack), !, get_prolog_backtrace_lc(MaxDepth, Stack, [frame(Fr)]), nlc. get_prolog_backtrace(MaxDepth, Stack, Options) :- get_prolog_backtrace_lc(MaxDepth, Stack, Options), nlc. % avoid last-call-optimization, such that % the top of the stack is always a nice Prolog % frame nlc. get_prolog_backtrace_lc(MaxDepth, Stack, Options) :- ( option(frame(Fr), Options) -> PC = call ; prolog_current_frame(Fr0), prolog_frame_attribute(Fr0, pc, PC), prolog_frame_attribute(Fr0, parent, Fr) ), ( option(goal_term_depth(GoalDepth), Options) -> true ; current_prolog_flag(backtrace_goal_depth, GoalDepth) ), option(guard(Guard), Options, none), ( def_no_clause_refs(Guard) -> DefClauseRefs = false ; DefClauseRefs = true ), option(clause_references(ClauseRefs), Options, DefClauseRefs), must_be(nonneg, GoalDepth), backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, Stack, Options). def_no_clause_refs(system:catch_with_backtrace/3). backtrace(0, _, _, _, _, _, [], _) :- !. backtrace(MaxDepth, Fr, PC, GoalDepth, Guard, ClauseRefs, [frame(Level, Where, Goal)|Stack], Options) :- prolog_frame_attribute(Fr, level, Level), ( PC == foreign -> prolog_frame_attribute(Fr, predicate_indicator, Pred), Where = foreign(Pred) ; PC == call -> prolog_frame_attribute(Fr, predicate_indicator, Pred), Where = call(Pred) ; prolog_frame_attribute(Fr, clause, Clause) -> clause_where(ClauseRefs, Clause, PC, Where, Options) ; Where = meta_call ), ( Where == meta_call -> Goal = 0 ; copy_goal(GoalDepth, Fr, Goal) ), ( prolog_frame_attribute(Fr, pc, PC2) -> true ; PC2 = foreign ), ( prolog_frame_attribute(Fr, parent, Parent), prolog_frame_attribute(Parent, predicate_indicator, PI), PI == Guard % last frame -> backtrace(1, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) ; prolog_frame_attribute(Fr, parent, Parent), more_stack(Parent) -> D2 is MaxDepth - 1, backtrace(D2, Parent, PC2, GoalDepth, Guard, ClauseRefs, Stack, Options) ; Stack = [] ). more_stack(Parent) :- prolog_frame_attribute(Parent, predicate_indicator, PI), \+ ( PI = ('$toplevel':G), G \== (toplevel_call/1) ), !. more_stack(_) :- current_prolog_flag(break_level, Break), Break >= 1. %! clause_where(+UseClauseRef, +Clause, +PC, -Where, +Options) is det. % % Get a description of the frame source location from Clause and the % PC inside clause. If UseClauseRef is `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. clause_where(true, Clause, PC, clause(Clause, PC), _). clause_where(false, Clause, PC, pred_line(PredName, File:Line), Options) :- option(subgoal_positions(true), Options, true), subgoal_position(Clause, PC, File, CharA, _CharZ), File \= @(_), % XPCE Object reference lineno(File, CharA, Line), clause_predicate_name(Clause, PredName), !. clause_where(false, Clause, _PC, pred_line(PredName, File:Line), _Options) :- clause_property(Clause, file(File)), clause_property(Clause, line_count(Line)), clause_predicate_name(Clause, PredName), !. clause_where(false, Clause, _PC, clause_name(ClauseName), _Options) :- clause_name(Clause, ClauseName). %! copy_goal(+TermDepth, +Frame, -Goal) is det. % % Create a shallow copy of the frame's goal to help debugging. In % addition to shallow copying, high-arity terms are represented % as below. Currently the 16 first arguments are hardcoded. % % == % name(A1, ..., A16, , An) % == copy_goal(0, _, 0) :- !. % 0 is not a valid goal copy_goal(D, Fr, Goal) :- prolog_frame_attribute(Fr, goal, Goal0), ( Goal0 = Module:Goal1 -> copy_term_limit(D, Goal1, Goal2), ( hidden_module(Module) -> Goal = Goal2 ; Goal = Module:Goal2 ) ; copy_term_limit(D, Goal0, Goal) ). hidden_module(system). hidden_module(user). copy_term_limit(0, In, '...') :- compound(In), !. copy_term_limit(N, In, Out) :- is_dict(In), !, dict_pairs(In, Tag, PairsIn), N2 is N - 1, MaxArity = 16, copy_pairs(PairsIn, N2, MaxArity, PairsOut), dict_pairs(Out, Tag, PairsOut). copy_term_limit(N, In, Out) :- compound(In), !, compound_name_arity(In, Functor, Arity), N2 is N - 1, MaxArity = 16, ( Arity =< MaxArity -> compound_name_arity(Out, Functor, Arity), copy_term_args(0, Arity, N2, In, Out) ; OutArity is MaxArity+2, compound_name_arity(Out, Functor, OutArity), copy_term_args(0, MaxArity, N2, In, Out), SkipArg is MaxArity+1, Skipped is Arity - MaxArity - 1, format(atom(Msg), '', [Skipped, Arity]), arg(SkipArg, Out, Msg), arg(Arity, In, InA), arg(OutArity, Out, OutA), copy_term_limit(N2, InA, OutA) ). copy_term_limit(_, In, Out) :- copy_term_nat(In, Out). copy_term_args(I, Arity, Depth, In, Out) :- I < Arity, !, I2 is I + 1, arg(I2, In, InA), arg(I2, Out, OutA), copy_term_limit(Depth, InA, OutA), copy_term_args(I2, Arity, Depth, In, Out). copy_term_args(_, _, _, _, _). copy_pairs([], _, _, []) :- !. copy_pairs(Pairs, _, 0, [''-Skipped]) :- !, length(Pairs, Skipped). copy_pairs([K-V0|T0], N, MaxArity, [K-V|T]) :- copy_term_limit(N, V0, V), MaxArity1 is MaxArity - 1, copy_pairs(T0, N, MaxArity1, T). %! prolog_stack_frame_property(+Frame, ?Property) is nondet. % % True when Property is a property of Frame. Frame is an element % of a stack-trace as produced by get_prolog_backtrace/2. Defined % properties are: % % * level(Level) % * predicate(PI) % * location(File:Line) prolog_stack_frame_property(frame(Level,_,_), level(Level)). prolog_stack_frame_property(frame(_,Where,_), predicate(PI)) :- frame_predicate(Where, PI). prolog_stack_frame_property(frame(_,clause(Clause,PC),_), location(File:Line)) :- subgoal_position(Clause, PC, File, CharA, _CharZ), File \= @(_), % XPCE Object reference lineno(File, CharA, Line). prolog_stack_frame_property(frame(_,_,_,Goal), goal(Goal)) :- Goal \== 0. frame_predicate(foreign(PI), PI). frame_predicate(call(PI), PI). frame_predicate(clause(Clause, _PC), PI) :- clause_property(Clause, predicate(PI)). default_backtrace_options(Options) :- ( current_prolog_flag(backtrace_show_lines, true), current_prolog_flag(iso, false) -> Options = [] ; Options = [subgoal_positions(false)] ). %! print_prolog_backtrace(+Stream, +Backtrace) is det. %! print_prolog_backtrace(+Stream, +Backtrace, +Options) is det. % % Print a stacktrace in human readable form to Stream. % Options is an option list that accepts: % % * subgoal_positions(+Boolean) % If =true=, print subgoal line numbers. The default depends % on the Prolog flag =backtrace_show_lines=. % % @arg Backtrace is a list of frame(Depth,Location,Goal) terms. print_prolog_backtrace(Stream, Backtrace) :- print_prolog_backtrace(Stream, Backtrace, []). print_prolog_backtrace(Stream, Backtrace, Options) :- default_backtrace_options(DefOptions), merge_options(Options, DefOptions, FinalOptions), phrase(message(Backtrace, FinalOptions), Lines), print_message_lines(Stream, '', Lines). :- public % Called from some handlers message//1. message(Backtrace) --> {default_backtrace_options(Options)}, message(Backtrace, Options). message(Backtrace, Options) --> message_frames(Backtrace, Options), warn_nodebug(Backtrace). message_frames([], _) --> []. message_frames([H|T], Options) --> message_frames(H, Options), ( {T == []} -> [] ; [nl], message_frames(T, Options) ). message_frames(frame(Level, Where, 0), Options) --> !, level(Level), where_no_goal(Where, Options). message_frames(frame(Level, _Where, '$toplevel':toplevel_call(_)), _) --> !, level(Level), [ ''-[] ]. message_frames(frame(Level, Where, Goal), Options) --> level(Level), [ ansi(code, '~p', [Goal]) ], where_goal(Where, Options). where_no_goal(foreign(PI), _) --> [ '~w '-[PI] ]. where_no_goal(call(PI), _) --> [ '~w'-[PI] ]. where_no_goal(pred_line(PredName, File:Line), _) --> !, [ '~w at '-[PredName], url(File:Line) ]. where_no_goal(clause_name(ClauseName), _) --> !, [ '~w '-[ClauseName] ]. where_no_goal(clause(Clause, PC), Options) --> { nonvar(Clause), !, clause_where(false, Clause, PC, Where, Options) }, where_no_goal(Where, Options). where_no_goal(meta_call, _) --> [ '' ]. where_goal(foreign(_), _) --> [ ' '-[] ], !. where_goal(pred_line(_PredName, File:Line), _) --> !, [ ' at ', url(File:Line) ]. where_goal(clause_name(ClauseName), _) --> !, [ '~w '-[ClauseName] ]. where_goal(clause(Clause, PC), Options) --> { nonvar(Clause), !, clause_where(false, Clause, PC, Where, Options) }, where_goal(Where, Options). where_goal(clause(Clause, _PC), _) --> { clause_property(Clause, file(File)), clause_property(Clause, line_count(Line)) }, !, [ ' at ', url(File:Line) ]. where_goal(clause(Clause, _PC), _) --> { clause_name(Clause, ClauseName) }, !, [ ' ~w '-[ClauseName] ]. where_goal(_, _) --> []. level(Level) --> [ '~|~t[~D]~6+ '-[Level] ]. warn_nodebug(Backtrace) --> { contiguous(Backtrace) }, !. warn_nodebug(_Backtrace) --> [ nl,nl, 'Note: some frames are missing due to last-call optimization.'-[], nl, 'Re-run your program in debug mode (:- debug.) to get more detail.'-[] ]. contiguous([frame(D0,_,_)|Frames]) :- contiguous(Frames, D0). contiguous([], _). contiguous([frame(D1,_,_)|Frames], D0) :- D1 =:= D0-1, contiguous(Frames, D1). %! clause_predicate_name(+ClauseRef, -Predname) is det. % % Produce a name (typically Functor/Arity) for a predicate to % which Clause belongs. :- multifile user:prolog_clause_name/2. clause_predicate_name(Clause, PredName) :- user:prolog_clause_name(Clause, PredName), !. clause_predicate_name(Clause, PredName) :- nth_clause(Head, _N, Clause), !, predicate_name(user:Head, PredName). %! backtrace(+MaxDepth) % % Get and print a stacktrace to the user_error stream. backtrace(MaxDepth) :- get_prolog_backtrace_lc(MaxDepth, Stack, []), print_prolog_backtrace(user_error, Stack). subgoal_position(ClauseRef, PC, File, CharA, CharZ) :- debug(backtrace, 'Term-position in ~p at PC=~w:', [ClauseRef, PC]), clause_info(ClauseRef, File, TPos, _), '$clause_term_position'(ClauseRef, PC, List), debug(backtrace, '\t~p~n', [List]), find_subgoal(List, TPos, PosTerm), arg(1, PosTerm, CharA), arg(2, PosTerm, CharZ). %! find_subgoal(+PosList, +TermPos, -SubGoalPos). % % @see Same as find_subgoal/3 in trace.pl from the GUI tracer. find_subgoal(_, Pos, Pos) :- var(Pos), !. find_subgoal([A|T], term_position(_, _, _, _, PosL), SPos) :- nth1(A, PosL, Pos), !, find_subgoal(T, Pos, SPos). find_subgoal([1|T], brace_term_position(_,_,Pos), SPos) :- !, find_subgoal(T, Pos, SPos). find_subgoal(List, parentheses_term_position(_,_,Pos), SPos) :- !, find_subgoal(List, Pos, SPos). find_subgoal(_, Pos, Pos). %! lineno(+File, +Char, -Line) % % Translate a character location to a line-number. Note that this % calls prolog_clause:try_open_source/2, but this is always loaded as % we would not have clause info without. lineno(File, Char, Line) :- setup_call_cleanup( ( prolog_clause:try_open_source(File, Fd), set_stream(Fd, newline(detect)) ), lineno_(Fd, Char, Line), close(Fd)). lineno_(Fd, Char, L) :- stream_property(Fd, position(Pos)), stream_position_data(char_count, Pos, C), C > Char, !, stream_position_data(line_count, Pos, L0), L is L0-1. lineno_(Fd, Char, L) :- skip(Fd, 0'\n), lineno_(Fd, Char, L). /******************************* * CHOICEPOINTS * *******************************/ %! print_last_choicepoint is det. % % Print details on the last open choice point. print_last_choicepoint :- prolog_current_choice(ChI0), % Choice in print_last_choicepoint/0 prolog_choice_attribute(ChI0, parent, ChI1), print_last_choicepoint(ChI1, []). print_last_choicepoint. %! print_last_choicepoint(+ChoiceRef, +Options) is det. print_last_choicepoint(ChI1, Options) :- real_choice(ChI1, ChI), prolog_choice_attribute(ChI, frame, F), prolog_frame_attribute(F, goal, Goal), Goal \= '$execute_goal2'(_,_,_), % Toplevel REPL choicepoint !, option(message_level(Level), Options, warning), get_prolog_backtrace(2, [_|Stack], [frame(F)]), ( predicate_property(Goal, foreign) -> print_message(Level, choicepoint(foreign(Goal), Stack)) ; prolog_frame_attribute(F, clause, Clause), ( prolog_choice_attribute(ChI, pc, PC) -> Ctx = jump(PC) ; prolog_choice_attribute(ChI, clause, Next) -> Ctx = clause(Next) ), print_message(Level, choicepoint(clause(Goal, Clause, Ctx), Stack)) ). print_last_choicepoint(_, _). real_choice(Ch0, Ch) :- prolog_choice_attribute(Ch0, type, Type), dummy_type(Type), !, prolog_choice_attribute(Ch0, parent, Ch1), real_choice(Ch1, Ch). real_choice(Ch, Ch). dummy_type(debug). dummy_type(none). prolog:message(choicepoint(Choice, Stack)) --> choice(Choice), [ nl, 'Called from', nl ], message(Stack). choice(foreign(Goal)) --> success_goal(Goal, 'a foreign choice point'). choice(clause(Goal, ClauseRef, clause(Next))) --> success_goal(Goal, 'a choice point in alternate clause'), [ nl ], [ ' ' ], clause_descr(ClauseRef), [': clause succeeded', nl], [ ' ' ], clause_descr(Next), [': next candidate clause' ]. choice(clause(Goal, ClauseRef, jump(PC))) --> { clause_where(false, ClauseRef, PC, Where, [subgoal_positions(true)]) }, success_goal(Goal, 'an in-clause choice point'), [ nl, ' ' ], where_no_goal(Where). success_goal(Goal, Reason) --> [ ansi(code, '~p', [Goal]), ' left ~w (after success)'-[Reason] ]. where_no_goal(pred_line(_PredName, File:Line)) --> !, [ url(File:Line) ]. where_no_goal(clause_name(ClauseName)) --> !, [ '~w '-[ClauseName] ]. clause_descr(ClauseRef) --> { clause_property(ClauseRef, file(File)), clause_property(ClauseRef, line_count(Line)) }, !, [ url(File:Line) ]. clause_descr(ClauseRef) --> { clause_name(ClauseRef, Name) }, [ '~w'-[Name] ]. /******************************* * DECORATE ERRORS * *******************************/ %! prolog_stack:stack_guard(+PI) is semidet. % % Dynamic multifile hook that is normally not defined. The hook is % called with PI equal to =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: % % * backtrace_depth % Integer that controls the maximum number of frames % collected. Default is 20. If a guard is specified, callers % of the guard are removed from the stack-trace. % % * backtrace_show_lines % Boolean that indicates whether the library tries to find % line numbers for the calls. Default is =true=. :- multifile user:prolog_exception_hook/4. :- dynamic user:prolog_exception_hook/4. user:prolog_exception_hook(error(E, context(Ctx0,Msg)), error(E, context(prolog_stack(Stack),Msg)), Fr, GuardSpec) :- current_prolog_flag(backtrace, true), \+ is_stack(Ctx0, _Frames), ( atom(GuardSpec) -> debug(backtrace, 'Got uncaught (guard = ~q) exception ~p (Ctx0=~p)', [GuardSpec, E, Ctx0]), stack_guard(GuardSpec), Guard = GuardSpec ; prolog_frame_attribute(GuardSpec, predicate_indicator, Guard), debug(backtrace, 'Got exception ~p (Ctx0=~p, Catcher=~p)', [E, Ctx0, Guard]), stack_guard(Guard) ), ( current_prolog_flag(backtrace_depth, Depth) -> Depth > 0 ; Depth = 20 % Thread created before lib was loaded ), get_prolog_backtrace(Depth, Stack0, [ frame(Fr), guard(Guard) ]), debug(backtrace, 'Stack = ~p', [Stack0]), clean_stack(Stack0, Stack1), join_stacks(Ctx0, Stack1, Stack). clean_stack(List, List) :- stack_guard(X), var(X), !. % Do not stop if we catch all clean_stack(List, Clean) :- clean_stack2(List, Clean). clean_stack2([], []). clean_stack2([H|_], [H]) :- guard_frame(H), !. clean_stack2([H|T0], [H|T]) :- clean_stack2(T0, T). guard_frame(frame(_,clause(ClauseRef, _, _))) :- nth_clause(M:Head, _, ClauseRef), functor(Head, Name, Arity), stack_guard(M:Name/Arity). join_stacks(Ctx0, Stack1, Stack) :- nonvar(Ctx0), Ctx0 = prolog_stack(Stack0), is_list(Stack0), !, append(Stack0, Stack1, Stack). join_stacks(_, Stack, Stack). %! stack_guard(+Reason) is semidet. % % Dynamic multifile predicate. It is called with `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. stack_guard(none). stack_guard(system:catch_with_backtrace/3). /******************************* * MESSAGES * *******************************/ :- multifile prolog:message//1. prolog:message(error(Error, context(Stack, Message))) --> { Message \== 'DWIM could not correct goal', is_stack(Stack, Frames) }, !, '$messages':translate_message(error(Error, context(_, Message))), [ nl, 'In:', nl ], ( {is_list(Frames)} -> message(Frames) ; ['~w'-[Frames]] ). is_stack(Stack, Frames) :- nonvar(Stack), Stack = prolog_stack(Frames).