001/*
002 * Java Genetic Algorithm Library (jenetics-7.2.0).
003 * Copyright (c) 2007-2023 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020package io.jenetics.ext.internal.parser;
021
022import static java.lang.String.format;
023import static java.util.Objects.requireNonNull;
024
025import java.util.function.Predicate;
026
027/**
028 * Parser implementation for parsing a given token sequences.
029 *
030 * @param <T> the token type
031 *
032 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
033 * @since 7.1
034 * @version 7.1
035 */
036public class Parser<T> {
037
038        private final Tokenizer<T> _tokenizer;
039        private final TokenRing<T> _lookahead;
040
041        /**
042         * Create a new parser object with the given {@code tokenizer} and lookahead
043         * count {@code k}.
044         *
045         * @param tokenizer the token source {@code this} parser uses
046         * @param k the lookahead count
047         */
048        public Parser(final Tokenizer<T> tokenizer, final int k) {
049                _tokenizer = requireNonNull(tokenizer);
050                _lookahead = new TokenRing<>(k);
051                for (int i = 0; i < k; ++i) {
052                        consume();
053                }
054        }
055
056        /**
057         * Return the lookahead token with the given index. The index starts at
058         * {@code 1}. The returned token might be {@code null}.
059         *
060         * @param index lookahead index
061         * @return the token at the given index
062         */
063        public T LT(final int index) {
064                return _lookahead.LT(index);
065        }
066
067        /**
068         * Try to <em>match</em> and consume the next token of the given
069         * {@code type}. If the current token is not from the given type, a
070         * {@link ParsingException} is thrown.
071         *
072         * @param token the token type to match
073         * @return the matched token
074         * @throws ParsingException if the current token doesn't match the desired
075         *         {@code token}
076         */
077        public T match(final Predicate<? super T> token) {
078                final var next = LT(1);
079                if (token.test(next)) {
080                        consume();
081                        return next;
082                } else {
083                        throw new ParsingException(format(
084                                "Found unexpected token: %s.", LT(1)
085                        ));
086                }
087        }
088
089        /**
090         * Consumes the next token.
091         */
092        public void consume() {
093                _lookahead.add(_tokenizer.next());
094        }
095
096}