01 /*
02 * Java Genetic Algorithm Library (jenetics-7.1.0).
03 * Copyright (c) 2007-2022 Franz Wilhelmstötter
04 *
05 * Licensed under the Apache License, Version 2.0 (the "License");
06 * you may not use this file except in compliance with the License.
07 * You may obtain a copy of the License at
08 *
09 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 * Author:
18 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
19 */
20 package io.jenetics.ext.internal.parser;
21
22 import static java.lang.String.format;
23 import static java.util.Objects.requireNonNull;
24
25 import java.util.function.Predicate;
26
27 /**
28 * Parser implementation for parsing a given token sequences.
29 *
30 * @param <T> the token type
31 *
32 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
33 * @since 7.1
34 * @version 7.1
35 */
36 public class Parser<T> {
37
38 private final Tokenizer<T> _tokenizer;
39 private final TokenRing<T> _lookahead;
40
41 /**
42 * Create a new parser object with the given {@code tokenizer} and lookahead
43 * count {@code k}.
44 *
45 * @param tokenizer the token source {@code this} parser uses
46 * @param k the lookahead count
47 */
48 public Parser(final Tokenizer<T> tokenizer, final int k) {
49 _tokenizer = requireNonNull(tokenizer);
50 _lookahead = new TokenRing<>(k);
51 for (int i = 0; i < k; ++i) {
52 consume();
53 }
54 }
55
56 /**
57 * Return the lookahead token with the given index. The index starts at
58 * {@code 1}. The returned token might be {@code null}.
59 *
60 * @param index lookahead index
61 * @return the token at the given index
62 */
63 public T LT(final int index) {
64 return _lookahead.LT(index);
65 }
66
67 /**
68 * Try to <em>match</em> and consume the next token of the given
69 * {@code type}. If the current token is not from the given type, a
70 * {@link ParsingException} is thrown.
71 *
72 * @param token the token type to match
73 * @return the matched token
74 * @throws ParsingException if the current token doesn't match the desired
75 * {@code token}
76 */
77 public T match(final Predicate<? super T> token) {
78 final var next = LT(1);
79 if (token.test(next)) {
80 consume();
81 return next;
82 } else {
83 throw new ParsingException(format(
84 "Found unexpected token: %s.", LT(1)
85 ));
86 }
87 }
88
89 /**
90 * Consumes the next token.
91 */
92 public void consume() {
93 _lookahead.add(_tokenizer.next());
94 }
95
96 }
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