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)  1985-2011, University of Amsterdam
   7                              VU University Amsterdam
   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(swi_system_utilities,
  37        [ lock_predicate/1,
  38          unlock_predicate/1,
  39          system_mode/1,
  40          system_module/0
  41        ]).
  42:- use_module(library(error)).
  43
  44/** <module> System utilities
  45
  46This module provides some tools to deal with system predicates. System
  47predicates cannot be traced or redefined.
  48
  49@deprecated     Use :- set_prolog_flag(generate_debug_info, false) to
  50                hide predicate internals from the tracer.
  51@tbd            Move this functionality to prolog flags.
  52*/
  53
  54%!  system_mode(+Boolean) is det.
  55%
  56%   Switch the system into system or user mode.  When in system mode,
  57%   system predicates loose most of their special properties, so it
  58%   becomes possible to trace and even redefine them.
  59%
  60%   @deprecated  New code should use the prolog flag =access_level=.
  61
  62system_mode(Val) :-
  63    must_be(boolean, Val),
  64    (   Val == true
  65    ->  set_prolog_flag(access_level, system)
  66    ;   set_prolog_flag(access_level, user)
  67    ).
  68
  69%!  system_module
  70%
  71%   Any predicate defined after this declaraction   uptil the end of
  72%   the file will become a system   predicate. Normally invoked by a
  73%   directive immediately following the module declaration.
  74
  75system_module :-
  76    set_prolog_flag(generate_debug_info, false).
  77
  78:- meta_predicate
  79    lock_predicate(:),
  80    unlock_predicate(:).
  81
  82%!  lock_predicate(+PredInd)
  83%
  84%   Transform a predicate into a system predicate.
  85
  86lock_predicate(PredInd) :-
  87    '$set_predicate_attribute'(PredInd, system, true).
  88
  89%!  unlock_predicate(+PredInd)
  90%
  91%   Transform a system predicate into a normal system predicate.
  92
  93unlock_predicate(PredInd) :-
  94    '$set_predicate_attribute'(PredInd, system, false).