/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2004-2013, University of Amsterdam VU University Amsterdam All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- 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 ]). /** 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. :- '$notransact'(operator_stack/1). :- meta_predicate push_operators(:), push_operators(:,-), push_op(+,+,:). %! 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), asserta(operator_stack(mark-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, A) :- undo_operator(op(P,T,A), Undo), op(P, T, A), asserta(operator_stack(incremental-Undo)). %! pop_operators is det. % % Revert all changes to the operator table realised since the last % push_operators/1. pop_operators :- retract(operator_stack(Mark-Undo)), set_operators(Undo), Mark == mark, !. %! 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]) :- strip_module(M:N0, M1, N1), N = M1:N1, 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(xf, postfix). op_type(yf, postfix).