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) 2004-2013, 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(prolog_operator, 37 [ push_operators/1, % +List 38 push_operators/2, % +List, -Undo 39 pop_operators/0, 40 pop_operators/1, % +Undo 41 push_op/3 % Precedence, Type, Name 42 ]). 43 44 45/** <module> Manage operators 46 47Often, one wants to define operators to improve the readibility of some 48very specific code. Operators in Prolog are global objects and changing 49operators changes syntax and possible semantics of existing sources. For 50this reason it is desirable to reset operator declarations after the 51code that needs them has been read. This module defines a rather cruel 52-but portable- method to do this. 53 54Usage: 55 56== 57:- push_operators( 58 [ op(900, fx, hello_world) 59 , op(600, xf, *) 60 ]). 61 62hello_world World :- 63 .... 64 65:- pop_operators. 66== 67 68While the above are for source-code, the calls push_operators/2 and 69pop_operators/1 can be used for local processing where it is more 70comfortable to carry the undo context around. 71 72NOTE: In recent versions of SWI-Prolog operators are local to a module 73and can be exported using the syntax below. This is not portable, but 74otherwise a more structured approach for operator handling. 75 76== 77:- module(mymodule, 78 [ mypred/1, 79 op(500, fx, myop) 80 ]). 81== 82 83@compat SWI-Prolog 84*/ 85 86:- thread_local 87 operator_stack/1. 88:- '$notransact'(operator_stack/1). 89 90:- meta_predicate 91 push_operators(), 92 push_operators(,), 93 push_op(,,). 94 95%! push_operators(:New) is det. 96%! push_operators(:New, -Undo) is det. 97% 98% Installs the operators from New, where New is a list of op(Prec, 99% Type, :Name). The modifications to the operator table are undone 100% in a matching call to pop_operators/0. 101 102push_operators(New, Undo) :- 103 strip_module(New, Module, Ops0), 104 tag_ops(Ops0, Module, Ops), 105 undo_operators(Ops, Undo), 106 set_operators(Ops). 107 108push_operators(New) :- 109 push_operators(New, Undo), 110 asserta(operator_stack(mark-Undo)). 111 112%! push_op(+Precedence, +Type, :Name) is det. 113% 114% As op/3, but this call must appear between push_operators/1 and 115% pop_operators/0. The change is undone by the call to 116% pop_operators/0 117 118push_op(P, T, A) :- 119 undo_operator(op(P,T,A), Undo), 120 op(P, T, A), 121 asserta(operator_stack(incremental-Undo)). 122 123%! pop_operators is det. 124% 125% Revert all changes to the operator table realised since the last 126% push_operators/1. 127 128pop_operators :- 129 retract(operator_stack(Mark-Undo)), 130 set_operators(Undo), 131 Mark == mark, 132 !. 133 134%! pop_operators(+Undo) is det. 135% 136% Reset operators as pushed by push_operators/2. 137 138pop_operators(Undo) :- 139 set_operators(Undo). 140 141tag_ops([], _, []). 142tag_ops([op(P,Tp,N0)|T0], M, [op(P,Tp,N)|T]) :- 143 strip_module(M:N0, M1, N1), 144 N = M1:N1, 145 tag_ops(T0, M, T). 146 147set_operators([]). 148set_operators([H|R]) :- 149 set_operators(H), 150 set_operators(R). 151set_operators(op(P,T,A)) :- 152 op(P, T, A). 153 154undo_operators([], []). 155undo_operators([O0|T0], [U0|T]) :- 156 undo_operator(O0, U0), 157 undo_operators(T0, T). 158 159undo_operator(op(_P, T, N), op(OP, OT, N)) :- 160 current_op(OP, OT, N), 161 same_op_type(T, OT), 162 !. 163undo_operator(op(P, T, [H|R]), [OH|OT]) :- 164 !, 165 undo_operator(op(P, T, H), OH), 166 undo_operator(op(P, T, R), OT). 167undo_operator(op(_, _, []), []) :- !. 168undo_operator(op(_P, T, N), op(0, T, N)). 169 170same_op_type(T, OT) :- 171 op_type(T, Type), 172 op_type(OT, Type). 173 174op_type(fx, prefix). 175op_type(fy, prefix). 176op_type(xfx, infix). 177op_type(xfy, infix). 178op_type(yfx, infix). 179op_type(xf, postfix). 180op_type(yf, postfix)