/usr/lib/swi-prolog/library/operators.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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 | /* $Id$
Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: jan@swi.psy.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2004, 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(prolog_operator,
[ push_operators/1, % +List
push_operators/2, % +List, -Undo
pop_operators/0,
pop_operators/1, % +Undo
push_op/3 % Precedence, Type, Name
]).
/** <module> Manage operators
Often, one wants to define operators to improve the readibility of some
very specific code. Operators in Prolog are global objects and changing
operators changes syntax and possible semantics of existing sources. For
this reason it is desirable to reset operator declarations after the
code that needs them has been read. This module defines a rather cruel
-but portable- method to do this.
Usage:
==
:- push_operators(
[ op(900, fx, hello_world)
, op(600, xf, *)
]).
hello_world World :-
....
:- pop_operators.
==
While the above are for source-code, the calls push_operators/2 and
pop_operators/1 can be used for local processing where it is more
comfortable to carry the undo context around.
NOTE: In recent versions of SWI-Prolog operators are local to a module
and can be exported using the syntax below. This is not portable, but
otherwise a more structured approach for operator handling.
==
:- module(mymodule,
[ mypred/1,
op(500, fx, myop)
]).
==
@compat SWI-Prolog
*/
:- thread_local
operator_stack/1.
:- module_transparent
push_operators/1,
push_operators/2,
push_op/3.
%% push_operators(:New) is det.
%% push_operators(:New, -Undo) is det.
%
% Installs the operators from New, where New is a list of op(Prec,
% Type, :Name). The modifications to the operator table are undone
% in a matching call to pop_operators/0.
push_operators(New, Undo) :-
strip_module(New, Module, Ops0),
tag_ops(Ops0, Module, Ops),
undo_operators(Ops, Undo),
set_operators(Ops).
push_operators(New) :-
push_operators(New, Undo),
assert_op(mark),
assert_op(Undo).
%% push_op(+Precedence, +Type, :Name) is det.
%
% As op/3, but this call must appear between push_operators/1 and
% pop_operators/0. The change is undone by the call to
% pop_operators/0
push_op(P, T, A0) :-
( A0 = _:_
-> A = A0
; context_module(M),
A = M:A0
),
undo_operator(op(P,T,A), Undo),
assert_op(Undo),
op(P, T, A).
%% pop_operators is det.
%
% Revert all changes to the operator table realised since the last
% push_operators/1.
pop_operators :-
retract_op(Undo),
( Undo == mark
-> !
; set_operators(Undo),
fail
).
%% pop_operators(+Undo) is det.
%
% Reset operators as pushed by push_operators/2.
pop_operators(Undo) :-
set_operators(Undo).
tag_ops([], _, []).
tag_ops([op(P,Tp,N0)|T0], M, [op(P,Tp,N)|T]) :-
( N0 = _:_
-> N = N0
; N = M:N0
),
tag_ops(T0, M, T).
set_operators([]).
set_operators([H|R]) :-
set_operators(H),
set_operators(R).
set_operators(op(P,T,A)) :-
op(P, T, A).
undo_operators([], []).
undo_operators([O0|T0], [U0|T]) :-
undo_operator(O0, U0),
undo_operators(T0, T).
undo_operator(op(_P, T, N), op(OP, OT, N)) :-
current_op(OP, OT, N),
same_op_type(T, OT), !.
undo_operator(op(P, T, [H|R]), [OH|OT]) :- !,
undo_operator(op(P, T, H), OH),
undo_operator(op(P, T, R), OT).
undo_operator(op(_, _, []), []) :- !.
undo_operator(op(_P, T, N), op(0, T, N)).
same_op_type(T, OT) :-
op_type(T, Type),
op_type(OT, Type).
op_type(fx, prefix).
op_type(fy, prefix).
op_type(xfx, infix).
op_type(xfy, infix).
op_type(yfx, infix).
op_type(yfy, infix).
op_type(xf, postfix).
op_type(yf, postfix).
%% assert_op(+Term) is det.
%% retract_op(-Term) is det.
%
% Force local assert/retract.
assert_op(Term) :-
asserta(operator_stack(Term)).
retract_op(Term) :-
retract(operator_stack(Term)).
|