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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)  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)).

System utilities

This module provides some tools to deal with system predicates. System predicates cannot be traced or redefined.

deprecated
- Use :- set_prolog_flag(generate_debug_info, false) to hide predicate internals from the tracer.
To be done
- Move this functionality to prolog flags. */



 system_mode(+Boolean) is det
Switch the system into system or user mode. When in system mode,
system predicates loose most of their special properties, so it
becomes possible to trace and even redefine them.




deprecated
- New code should use the prolog flag access_level.







   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    ).



 system_module
Any predicate defined after this declaraction uptil the end of
the file will become a system predicate. Normally invoked by a
directive immediately following the module declaration.


   75system_module :-
   76    set_prolog_flag(generate_debug_info, false).
   77
   78:- meta_predicate
   79    lock_predicate(:),
   80    unlock_predicate(:).



 lock_predicate(+PredInd)
Transform a predicate into a system predicate.


   86lock_predicate(PredInd) :-
   87    '$set_predicate_attribute'(PredInd, system, true).



 unlock_predicate(+PredInd)
Transform a system predicate into a normal system predicate.


   93unlock_predicate(PredInd) :-
   94    '$set_predicate_attribute'(PredInd, system, false)