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.grammar;
021
022import static java.util.Objects.requireNonNull;
023
024import java.util.random.RandomGenerator;
025
026import io.jenetics.ext.grammar.Cfg.Rule;
027
028/**
029 * Functional interface for selecting a {@link Cfg.Symbol} by its index within a
030 * rule. It is an abstraction of the <em>codon</em> values used for selecting
031 * the alternatives from a rule during the sentence generation.
032 *
033 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
034 * @since 7.1
035 * @version 7.1
036 */
037@FunctionalInterface
038public interface SymbolIndex {
039
040        /**
041         * Selects an index with the given upper {@code bound}, exclusively.
042         *
043         * @param rule the rule which requested the index
044         * @param bound the upper bound of the symbol index, exclusively
045         * @return the next symbol index
046         * @throws IllegalArgumentException if the given {@code bound} is smaller
047         *         than one
048         */
049        int next(final Rule<?> rule, final int bound);
050
051        /**
052         * Create a new symbol-index object from the given random generator. This
053         * can be used for generating random sentences of derivation-trees.
054         *
055         * @param random the random generator used for generating the sentences
056         * @return a new symbol-index object from the given random generator
057         * @throws NullPointerException if the given {@code random} generator is
058         *         {@code null}
059         */
060        static SymbolIndex of(final RandomGenerator random) {
061                requireNonNull(random);
062                return (rule, bound) -> random.nextInt(bound);
063        }
064
065}