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    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)  2002-2018, University of Amsterdam
    7                              VU University Amsterdam
    8                              CWI, Amsterdam
    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_debug,
   38          [ debug/3,                    % +Topic, +Format, :Args
   39            debug/1,                    % +Topic
   40            nodebug/1,                  % +Topic
   41            debugging/1,                % ?Topic
   42            debugging/2,                % ?Topic, ?Bool
   43            list_debug_topics/0,
   44            debug_message_context/1,    % (+|-)What
   45
   46            assertion/1                 % :Goal
   47          ]).   48:- use_module(library(error)).   49:- use_module(library(lists)).   50:- set_prolog_flag(generate_debug_info, false).   51
   52:- meta_predicate
   53    assertion(0),
   54    debug(+,+,:).   55
   56:- multifile prolog:assertion_failed/2.   57:- dynamic   prolog:assertion_failed/2.   58
   59/*:- use_module(library(prolog_stack)).*/ % We use the autoloader if needed
   60
   61%:- set_prolog_flag(generate_debug_info, false).
   62
   63:- dynamic
   64    debugging/3.                    % Topic, Enabled, To

Print debug messages and test assertions

This library is a replacement for format/3 for printing debug messages. Messages are assigned a topic. By dynamically enabling or disabling topics the user can select desired messages. Debug statements are removed when the code is compiled for optimization.

See manual for details. With XPCE, you can use the call below to start a graphical monitoring tool.

?- prolog_ide(debug_monitor).

Using the predicate assertion/1 you can make assumptions about your program explicit, trapping the debugger if the condition does not hold.

author
- Jan Wielemaker */
 debugging(+Topic) is semidet
debugging(-Topic) is nondet
 debugging(?Topic, ?Bool) is nondet
Examine debug topics. The form debugging(+Topic) may be used to perform more complex debugging tasks. A typical usage skeleton is:
      (   debugging(mytopic)
      ->  <perform debugging actions>
      ;   true
      ),
      ...

The other two calls are intended to examine existing and enabled debugging tokens and are typically not used in user programs.

  105debugging(Topic) :-
  106    debugging(Topic, true, _To).
  107
  108debugging(Topic, Bool) :-
  109    debugging(Topic, Bool, _To).
 debug(+Topic) is det
 nodebug(+Topic) is det
Add/remove a topic from being printed. nodebug(_) removes all topics. Gives a warning if the topic is not defined unless it is used from a directive. The latter allows placing debug topics at the start of a (load-)file without warnings.

For debug/1, Topic can be a term Topic > Out, where Out is either a stream or stream-alias or a filename (atom). This redirects debug information on this topic to the given output.

  123debug(Topic) :-
  124    with_mutex(prolog_debug, debug(Topic, true)).
  125nodebug(Topic) :-
  126    with_mutex(prolog_debug, debug(Topic, false)).
  127
  128debug(Spec, Val) :-
  129    debug_target(Spec, Topic, Out),
  130    (   (   retract(debugging(Topic, Enabled0, To0))
  131        *-> update_debug(Enabled0, To0, Val, Out, Enabled, To),
  132            assert(debugging(Topic, Enabled, To)),
  133            fail
  134        ;   (   prolog_load_context(file, _)
  135            ->  true
  136            ;   print_message(warning, debug_no_topic(Topic))
  137            ),
  138            update_debug(false, [], Val, Out, Enabled, To),
  139            assert(debugging(Topic, Enabled, To))
  140        )
  141    ->  true
  142    ;   true
  143    ).
  144
  145debug_target(Spec, Topic, To) :-
  146    nonvar(Spec),
  147    Spec = (Topic > To),
  148    !.
  149debug_target(Topic, Topic, -).
  150
  151update_debug(_, To0, true, -, true, To) :-
  152    !,
  153    ensure_output(To0, To).
  154update_debug(true, To0, true, Out, true, Output) :-
  155    !,
  156    (   memberchk(Out, To0)
  157    ->  Output = To0
  158    ;   append(To0, [Out], Output)
  159    ).
  160update_debug(false, _, true, Out, true, [Out]) :- !.
  161update_debug(_, _, false, -, false, []) :- !.
  162update_debug(true, [Out], false, Out, false, []) :- !.
  163update_debug(true, To0, false, Out, true, Output) :-
  164    !,
  165    delete(To0, Out, Output).
  166
  167ensure_output([], [user_error]) :- !.
  168ensure_output(List, List).
 debug_topic(+Topic) is det
Declare a topic for debugging. This can be used to find all topics available for debugging.
  175debug_topic(Topic) :-
  176    (   debugging(Registered, _, _),
  177        Registered =@= Topic
  178    ->  true
  179    ;   assert(debugging(Topic, false, []))
  180    ).
 list_debug_topics is det
List currently known debug topics and their setting.
  186list_debug_topics :-
  187    format(user_error, '~`-t~45|~n', []),
  188    format(user_error, '~w~t ~w~35| ~w~n',
  189           ['Debug Topic', 'Activated', 'To']),
  190    format(user_error, '~`-t~45|~n', []),
  191    (   debugging(Topic, Value, To),
  192        format(user_error, '~w~t ~w~35| ~w~n', [Topic, Value, To]),
  193        fail
  194    ;   true
  195    ).
 debug_message_context(+What) is det
Specify additional context for debug messages.
deprecated
- New code should use the Prolog flag message_context. This predicates adds or deletes topics from this list.
  204debug_message_context(+Topic) :-
  205    current_prolog_flag(message_context, List),
  206    (   memberchk(Topic, List)
  207    ->  true
  208    ;   append(List, [Topic], List2),
  209        set_prolog_flag(message_context, List2)
  210    ).
  211debug_message_context(-Topic) :-
  212    current_prolog_flag(message_context, List),
  213    (   selectchk(Topic, List, Rest)
  214    ->  set_prolog_flag(message_context, Rest)
  215    ;   true
  216    ).
 debug(+Topic, +Format, :Args) is det
Format a message if debug topic is enabled. Similar to format/3 to user_error, but only prints if Topic is activated through debug/1. Args is a meta-argument to deal with goal for the @-command. Output is first handed to the hook debug_print_hook/3. If this fails, Format+Args is translated to text using the message-translation (see print_message/2) for the term debug(Format, Args) and then printed to every matching destination (controlled by debug/1) using print_message_lines/3.

The message is preceded by '% ' and terminated with a newline.

See also
- format/3.
  234debug(Topic, Format, Args) :-
  235    debugging(Topic, true, To),
  236    !,
  237    print_debug(Topic, To, Format, Args).
  238debug(_, _, _).
 prolog:debug_print_hook(+Topic, +Format, +Args) is semidet
Hook called by debug/3. This hook is used by the graphical frontend that can be activated using prolog_ide/1:
?- prolog_ide(debug_monitor).
  250:- multifile
  251    prolog:debug_print_hook/3.  252
  253print_debug(Topic, _To, Format, Args) :-
  254    prolog:debug_print_hook(Topic, Format, Args),
  255    !.
  256print_debug(_, [], _, _) :- !.
  257print_debug(Topic, To, Format, Args) :-
  258    phrase('$messages':translate_message(debug(Format, Args)), Lines),
  259    (   member(T, To),
  260        debug_output(T, Stream),
  261        with_output_to(
  262            Stream,
  263            print_message_lines(current_output, kind(debug(Topic)), Lines)),
  264        fail
  265    ;   true
  266    ).
  267
  268
  269debug_output(user, user_error) :- !.
  270debug_output(Stream, Stream) :-
  271    is_stream(Stream),
  272    !.
  273debug_output(File, Stream) :-
  274    open(File, append, Stream,
  275         [ close_on_abort(false),
  276           alias(File),
  277           buffer(line)
  278         ]).
  279
  280
  281                 /*******************************
  282                 *           ASSERTION          *
  283                 *******************************/
 assertion(:Goal) is det
Acts similar to C assert() macro. It has no effect if Goal succeeds. If Goal fails or throws an exception, the following steps are taken:
  299assertion(G) :-
  300    \+ \+ catch(G,
  301                Error,
  302                assertion_failed(Error, G)),
  303
  304    !.
  305assertion(G) :-
  306    assertion_failed(fail, G),
  307    assertion_failed.               % prevent last call optimization.
  308
  309assertion_failed(Reason, G) :-
  310    prolog:assertion_failed(Reason, G),
  311    !.
  312assertion_failed(Reason, _) :-
  313    assertion_rethrow(Reason),
  314    !,
  315    throw(Reason).
  316assertion_failed(Reason, G) :-
  317    print_message(error, assertion_failed(Reason, G)),
  318    backtrace(10),
  319    (   current_prolog_flag(break_level, _) % interactive thread
  320    ->  trace
  321    ;   throw(error(assertion_error(Reason, G), _))
  322    ).
  323
  324assertion_failed.
  325
  326assertion_rethrow(time_limit_exceeded).
  327assertion_rethrow('$aborted').
 assume(:Goal) is det
Acts similar to C assert() macro. It has no effect of Goal succeeds. If Goal fails it prints a message, a stack-trace and finally traps the debugger.
deprecated
- Use assertion/1 in new code.
  337                 /*******************************
  338                 *           EXPANSION          *
  339                 *******************************/
  340
  341%       The optimise_debug flag  defines whether  Prolog  optimizes
  342%       away assertions and  debug/3 statements.  Values are =true=
  343%       (debug is optimized away),  =false= (debug is retained) and
  344%       =default= (debug optimization is dependent on the optimise
  345%       flag).
  346
  347optimise_debug :-
  348    (   current_prolog_flag(optimise_debug, true)
  349    ->  true
  350    ;   current_prolog_flag(optimise_debug, default),
  351        current_prolog_flag(optimise, true)
  352    ->  true
  353    ).
  354
  355:- multifile
  356    system:goal_expansion/2.  357
  358system:goal_expansion(debug(Topic,_,_), true) :-
  359    (   optimise_debug
  360    ->  true
  361    ;   debug_topic(Topic),
  362        fail
  363    ).
  364system:goal_expansion(debugging(Topic), fail) :-
  365    (   optimise_debug
  366    ->  true
  367    ;   debug_topic(Topic),
  368        fail
  369    ).
  370system:goal_expansion(assertion(_), true) :-
  371    optimise_debug.
  372system:goal_expansion(assume(_), true) :-
  373    print_message(informational,
  374                  compatibility(renamed(assume/1, assertion/1))),
  375    optimise_debug.
  376
  377
  378                 /*******************************
  379                 *            MESSAGES          *
  380                 *******************************/
  381
  382:- multifile
  383    prolog:message/3.  384
  385prolog:message(assertion_failed(_, G)) -->
  386    [ 'Assertion failed: ~q'-[G] ].
  387prolog:message(debug(Fmt, Args)) -->
  388    [ Fmt-Args ].
  389prolog:message(debug_no_topic(Topic)) -->
  390    [ '~q: no matching debug topic (yet)'-[Topic] ].
  391
  392
  393                 /*******************************
  394                 *             HOOKS            *
  395                 *******************************/
 prolog:assertion_failed(+Reason, +Goal) is semidet
This hook is called if the Goal of assertion/1 fails. Reason is unified with either fail if Goal simply failed or an exception call otherwise. If this hook fails, the default behaviour is activated. If the hooks throws an exception it will be propagated into the caller of assertion/1.
  406                 /*******************************
  407                 *            SANDBOX           *
  408                 *******************************/
  409
  410:- multifile sandbox:safe_meta/2.  411
  412sandbox:safe_meta(prolog_debug:assertion(X), [X])