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)  2019-2021, CWI, Amsterdam
    7                              SWI-Prolog Solutions b.v.
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(prolog_trace,
   37          [ trace/1,                            % :Spec
   38            trace/2,                            % :Spec, +Ports
   39            tracing/2,                          % :Spec, -Ports
   40            notraceall/0
   41          ]).   42:- autoload(library(apply),[maplist/2]).   43:- autoload(library(error),[instantiation_error/1]).   44:- autoload(library(prolog_wrap),[wrap_predicate/4]).   45:- autoload(library(prolog_code), [pi_head/2]).

   57:- meta_predicate
   58    trace(:),
   59    trace(:, +),
   60    tracing(:, -).   61
   62:- dynamic tracing_mask/2.   63:- volatile tracing_mask/2.

 trace(:Pred) is det

 trace(:Pred, +PortSpec) is det

Print passes through ports of specified predicates. Pred is a, possible partial, specification of a predicate as it is also used be spy/1 and similar predicates. Where a full predicate specification is of the shape Module:Name/Arity (or `//Arity for non-terminals), both the module and arity may be omitted in which case Pred refers to all matching predicates. PortSpec is either a single port (call, exit, fail or redo), preceded with + or - or a list of these. The predicate modifies the current trace specification and then installs a suitable wrapper for the predicate using wrap_predicate/4. For example:

` ?- trace(append). % append/2: [all] % append/3: [all] % append/1: [all] true.

?- append([a,b], [c], L). T Call: lists:append([a, b], [c], _10478) T Call: lists:append([b], [c], _11316) T Call: lists:append([], [c], _11894) T Exit: lists:append([], [c], [c]) T Exit: lists:append([b], [c], [b, c]) T Exit: lists:append([a, b], [c], [a, b, c]) L = [a, b, c].

?- trace(append, -all). % append/2: Not tracing % append/3: Not tracing % append/1: Not tracing

Compatibility

- This library replaces prior built-in functionality. Unlike the built-in version, ports are printed regardless of the debug flag. The built-in version printed the call-stack depth. That is currently not provided by this replacement.

  105trace(Pred) :-
  106    trace(Pred, +all).
  107
  108trace(Pred, Spec) :-
  109    '$find_predicate'(Pred, Preds),
  110    Preds \== [],
  111    maplist(set_trace(Spec), Preds).
  112
  113set_trace(Spec, Pred) :-
  114    (   tracing_mask(Pred, Spec0)
  115    ->  true
  116    ;   Spec0 = 0
  117    ),
  118    modify(Spec, Spec0, Spec1),
  119    retractall(tracing_mask(Pred, _)),
  120    (   Spec1 == []
  121    ->  true
  122    ;   asserta(tracing_mask(Pred, Spec1))
  123    ),
  124    mask_ports(Spec1, Ports),
  125    pi_head(Pred, Head0),
  126    (   predicate_property(Head0, imported_from(M))
  127    ->  requalify(Head0, M, Head)
  128    ;   Head = Head0
  129    ),
  130    (   Spec1 == 0
  131    ->  unwrap_predicate(Head, trace),
  132        print_message(informational, trace(Head, Ports))
  133    ;   wrapper(Spec1, Head, Wrapped, Wrapper),
  134        wrap_predicate(Head, trace, Wrapped, Wrapper),
  135        print_message(informational, trace(Head, Ports))
  136    ).
  137
  138requalify(Term, M, M:Plain) :-
  139    strip_module(Term, _, Plain).
  140
  141modify(Var, _, _) :-
  142    var(Var),
  143    !,
  144    instantiation_error(Var).
  145modify([], Spec, Spec) :-
  146    !.
  147modify([H|T], Spec0, Spec) :-
  148    !,
  149    modify(H, Spec0, Spec1),
  150    modify(T, Spec1, Spec).
  151modify(+Port, Spec0, Spec) :-
  152    !,
  153    port_mask(Port, Mask),
  154    Spec is Spec0 \/ Mask.
  155modify(-Port, Spec0, Spec) :-
  156    !,
  157    port_mask(Port, Mask),
  158    Spec is Spec0 /\ \Mask.
  159modify(Port, Spec0, Spec) :-
  160    port_mask(Port, Mask),
  161    Spec is Spec0 \/ Mask.
  162
  163port_mask(all,  0x0f).
  164port_mask(call, 0x01).
  165port_mask(exit, 0x02).
  166port_mask(redo, 0x04).
  167port_mask(fail, 0x08).
  168
  169mask_ports(0, []) :-
  170    !.
  171mask_ports(Pattern, [H|T]) :-
  172    is_masked(Pattern, H, Pattern1),
  173    mask_ports(Pattern1, T).
  174
  175wrapper(Ports, Head, Wrapped, Wrapper) :-
  176    wrapper(Ports, Head, Id-Level, Wrapped, Wrapped1),
  177    Wrapper = (   prolog_current_frame(Id),
  178                  prolog_frame_attribute(Id, level, Level),
  179                  Wrapped1
  180              ).
  181
  182wrapper(0, _, _, Wrapped, Wrapped) :-
  183    !.
  184wrapper(Pattern, Head, Id, Wrapped, Call) :-
  185    is_masked(Pattern, call, Pattern1),
  186    !,
  187    wrapper(Pattern1, Head, Id, Wrapped, Call0),
  188    Call = (   print_message(debug, frame(Head, trace(call, Id))),
  189               Call0
  190           ).
  191wrapper(Pattern, Head, Id, Wrapped, Call) :-
  192    is_masked(Pattern, exit, Pattern1),
  193    !,
  194    wrapper(Pattern1, Head, Id, Wrapped, Call0),
  195    Call = (   Call0,
  196               print_message(debug, frame(Head, trace(exit, Id)))
  197           ).
  198wrapper(Pattern, Head, Id, Wrapped, Call) :-
  199    is_masked(Pattern, redo, Pattern1),
  200    !,
  201    wrapper(Pattern1, Head, Id, Wrapped, Call0),
  202    Call = (   call_cleanup(Call0, Det = true),
  203               (   Det == true
  204               ->  true
  205               ;   true
  206               ;   print_message(debug, frame(Head, trace(redo, Id))),
  207                   fail
  208               )
  209           ).
  210wrapper(Pattern, Head, Id, Wrapped, Call) :-
  211    is_masked(Pattern, fail, Pattern1),
  212    !,
  213    wrapper(Pattern1, Head, Id, Wrapped, Call0),
  214    Call = call((   call_cleanup(Call0, Det = true),
  215                    (   Det == true
  216                    ->  !
  217                    ;   true
  218                    )
  219                ;   print_message(debug, frame(Head, trace(fail, Id))),
  220                    fail
  221                )).
  222
  223is_masked(Pattern0, Port, Pattern) :-
  224    port_mask(Port, Mask),
  225    Pattern0 /\ Mask =:= Mask,
  226    !,
  227    Pattern is Pattern0 /\ \Mask.

 tracing(:Spec, -Ports)

True if Spec is traced using Ports

  233tracing(Spec, Ports) :-
  234    tracing_mask(Spec, Mask),
  235    mask_ports(Mask, Ports).

 notraceall is det

Remove all trace points

  241notraceall :-
  242    forall(tracing(M:Spec, _Ports),
  243           trace(M:Spec, -all))