%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  This file is part of Logtalk <https://logtalk.org/>
%  Copyright 1998-2021 Paulo Moura <pmoura@logtalk.org>
%  SPDX-License-Identifier: Apache-2.0
%
%  Licensed under the Apache License, Version 2.0 (the "License");
%  you may not use this file except in compliance with the License.
%  You may obtain a copy of the License at
%
%      http://www.apache.org/licenses/LICENSE-2.0
%
%  Unless required by applicable law or agreed to in writing, software
%  distributed under the License is distributed on an "AS IS" BASIS,
%  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%  See the License for the specific language governing permissions and
%  limitations under the License.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


:- object(calculator,
	implements(parsep)).

	parse(Expression, Value) :-
		phrase(expr(Value), Expression).

	expr(Z) --> term(X), "+", expr(Y), {Z is X + Y}.
	expr(Z) --> term(X), "-", expr(Y), {Z is X - Y}.
	expr(X) --> term(X).

	term(Z) --> number(X), "*", term(Y), {Z is X * Y}.
	term(Z) --> number(X), "/", term(Y), {Z is X / Y}.
	term(Z) --> number(Z).

	number(C) --> "+", number(C).
	number(C) --> "-", number(X), {C is -X}.
	number(X) --> [C], {0'0 =< C, C =< 0'9, X is C - 0'0}.

:- end_object.
