io.jenetics.ext.internal.parser.Parser Maven / Gradle / Ivy
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/*
* Java Genetic Algorithm Library (jenetics-8.1.0).
* Copyright (c) 2007-2024 Franz Wilhelmstötter
*
* 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.
*
* Author:
* Franz Wilhelmstötter ([email protected])
*/
package io.jenetics.ext.internal.parser;
import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import java.util.function.Predicate;
/**
* Parser implementation for parsing a given token sequences.
*
* @param the token type
*
* @author Franz Wilhelmstötter
* @since 7.1
* @version 7.1
*/
public class Parser {
private final Tokenizer _tokenizer;
private final TokenRing _lookahead;
/**
* Create a new parser object with the given {@code tokenizer} and lookahead
* count {@code k}.
*
* @param tokenizer the token source {@code this} parser uses
* @param k the lookahead count
*/
public Parser(final Tokenizer tokenizer, final int k) {
_tokenizer = requireNonNull(tokenizer);
_lookahead = new TokenRing<>(k);
for (int i = 0; i < k; ++i) {
consume();
}
}
/**
* Return the lookahead token with the given index. The index starts at
* {@code 1}. The returned token might be {@code null}.
*
* @param index lookahead index
* @return the token at the given index
*/
public T LT(final int index) {
return _lookahead.LT(index);
}
/**
* Try to match and consume the next token of the given
* {@code type}. If the current token is not from the given type, a
* {@link ParsingException} is thrown.
*
* @param token the token type to match
* @return the matched token
* @throws ParsingException if the current token doesn't match the desired
* {@code token}
*/
public T match(final Predicate token) {
final var next = LT(1);
if (token.test(next)) {
consume();
return next;
} else {
throw new ParsingException(format(
"Found unexpected token: %s.", LT(1)
));
}
}
/**
* Consumes the next token.
*/
public void consume() {
_lookahead.add(_tokenizer.next());
}
}