/usr/lib/swi-prolog/library/system.pl is in swi-prolog-nox 5.10.4-3ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 | /* $Id$
Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: jan@swi.psy.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2002, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(swi_system_utilities,
[ lock_predicate/1,
unlock_predicate/1,
system_mode/1,
system_module/0
]).
:- style_check(+dollar).
/** <module> 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.
@tbd Move this functionality to prolog flags.
*/
%% system_mode(?Boolean)
%
% 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. Use the latter
% with care as the system predicates call one another. This should
% once be fixed by defining all of them in a module ('$system'), so
% the user can savely remove them from module user.
%
% @bug This predicate both accepts true/false and on/off. New
% code must use true/false.
system_mode(X) :-
var(X), !,
( style_check(?(dollar))
-> X = true
; X = false
).
system_mode(True) :-
truth(True, true), !,
style_check(+dollar).
system_mode(True) :-
truth(True, false), !,
style_check(-dollar).
system_mode(Val) :-
must_be(boolean, Val).
truth(true, true).
truth(false, false).
truth(on, true).
truth(off, false).
%% system_module
%
% Any predicate defined after this declaraction uptill the end of
% the file will become a system predicate. Normally invoked by a
% directive immediately following the module declaration.
system_module :-
system_mode(on).
:- meta_predicate
lock_predicate(:),
unlock_predicate(:).
%% lock_predicate(+PredInd)
%
% Transform a predicate into a system predicate.
lock_predicate(PredInd) :-
'$set_predicate_attribute'(PredInd, system, 1).
%% unlock_predicate(+PredInd)
%
% Transform a system predicate into a normal system predicate.
unlock_predicate(PredInd) :-
'$set_predicate_attribute'(PredInd, system, 0).
|