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

   54:- meta_predicate
   55    trace(:),
   56    trace(:, +),
   57    tracing(:, -).   58
   59:- dynamic tracing_mask/2.   60:- 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.

  102trace(Pred) :-
  103    trace(Pred, +all).
  104
  105trace(Pred, Spec) :-
  106    '$find_predicate'(Pred, Preds),
  107    Preds \== [],
  108    maplist(set_trace(Spec), Preds).
  109
  110set_trace(Spec, Pred) :-
  111    (   tracing_mask(Pred, Spec0)
  112    ->  true
  113    ;   Spec0 = 0
  114    ),
  115    modify(Spec, Spec0, Spec1),
  116    retractall(tracing_mask(Pred, _)),
  117    asserta(tracing_mask(Pred, Spec1)),
  118    mask_ports(Spec1, Ports),
  119    pi_head(Pred, Head),
  120    (   Spec1 == 0
  121    ->  unwrap_predicate(Head, trace),
  122        print_message(informational, trace(Head, Ports))
  123    ;   wrapper(Spec1, Head, Wrapped, Wrapper),
  124        wrap_predicate(Head, trace, Wrapped, Wrapper),
  125        print_message(informational, trace(Head, Ports))
  126    ).
  127
  128modify(Var, _, _) :-
  129    var(Var),
  130    !,
  131    instantiation_error(Var).
  132modify([], Spec, Spec) :-
  133    !.
  134modify([H|T], Spec0, Spec) :-
  135    !,
  136    modify(H, Spec0, Spec1),
  137    modify(T, Spec1, Spec).
  138modify(+Port, Spec0, Spec) :-
  139    !,
  140    port_mask(Port, Mask),
  141    Spec is Spec0 \/ Mask.
  142modify(-Port, Spec0, Spec) :-
  143    !,
  144    port_mask(Port, Mask),
  145    Spec is Spec0 /\ \Mask.
  146modify(Port, Spec0, Spec) :-
  147    port_mask(Port, Mask),
  148    Spec is Spec0 \/ Mask.
  149
  150port_mask(all,  0x0f).
  151port_mask(call, 0x01).
  152port_mask(exit, 0x02).
  153port_mask(redo, 0x04).
  154port_mask(fail, 0x08).
  155
  156mask_ports(0, []) :-
  157    !.
  158mask_ports(Pattern, [H|T]) :-
  159    is_masked(Pattern, H, Pattern1),
  160    mask_ports(Pattern1, T).
  161
  162pi_head(M:PI, M:Head) :-
  163    !,
  164    pi_head(PI, Head).
  165pi_head(Name/Arity, Head) :-
  166    functor(Head, Name, Arity).
  167pi_head(Name//Arity0, Head) :-
  168    Arity is Arity0+1,
  169    functor(Head, Name, Arity).
  170
  171wrapper(0, _, Wrapped, Wrapped) :-
  172    !.
  173wrapper(Pattern, Head, Wrapped, Call) :-
  174    is_masked(Pattern, call, Pattern1),
  175    !,
  176    wrapper(Pattern1, Head, Wrapped, Call0),
  177    Call = (   print_message(debug, frame(Head, trace(call))),
  178               Call0
  179           ).
  180wrapper(Pattern, Head, Wrapped, Call) :-
  181    is_masked(Pattern, exit, Pattern1),
  182    !,
  183    wrapper(Pattern1, Head, Wrapped, Call0),
  184    Call = (   Call0,
  185               print_message(debug, frame(Head, trace(exit)))
  186           ).
  187wrapper(Pattern, Head, Wrapped, Call) :-
  188    is_masked(Pattern, redo, Pattern1),
  189    !,
  190    wrapper(Pattern1, Head, Wrapped, Call0),
  191    Call = (   call_cleanup(Call0, Det = true),
  192               (   Det == true
  193               ->  true
  194               ;   true
  195               ;   print_message(debug, frame(Head, trace(redo))),
  196                   fail
  197               )
  198           ).
  199wrapper(Pattern, Head, Wrapped, Call) :-
  200    is_masked(Pattern, fail, Pattern1),
  201    !,
  202    wrapper(Pattern1, Head, Wrapped, Call0),
  203    Call = call((   call_cleanup(Call0, Det = true),
  204                    (   Det == true
  205                    ->  !
  206                    ;   true
  207                    )
  208                ;   print_message(debug, frame(Head, trace(fail))),
  209                    fail
  210                )).
  211
  212is_masked(Pattern0, Port, Pattern) :-
  213    port_mask(Port, Mask),
  214    Pattern0 /\ Mask =:= Mask,
  215    !,
  216    Pattern is Pattern0 /\ \Mask.

 tracing(:Spec, -Ports)

True if Spec is traced using Ports

  222tracing(Spec, Ports) :-
  223    tracing_mask(Spec, Mask),
  224    mask_ports(Mask, Ports)