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.List;
025import java.util.function.Function;
026
027import io.jenetics.ext.grammar.Cfg.NonTerminal;
028import io.jenetics.ext.grammar.Cfg.Symbol;
029
030/**
031 * Generator interface for generating <em>sentences</em>/<em>derivation trees</em>
032 * from a given grammar.
033 *
034 * @param <T> the terminal token type of the grammar
035 * @param <R> the result type of the generator
036 *
037 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
038 * @since 7.1
039 * @version 7.1
040 */
041@FunctionalInterface
042public interface Generator<T, R> {
043
044        /**
045         * Generates a new sentence from the given grammar. If the generation of the
046         * sentence fails, an empty list is returned.
047         *
048         * @param cfg the generating grammar
049         * @return a newly created result
050         */
051        R generate(final Cfg<? extends T> cfg);
052
053        /**
054         * Maps the generated result from type {@code R} to type {@code R1}.
055         *
056         * @param f the mapping function
057         * @param <R1> the target type
058         * @return a new generator with target type {@code R1}
059         * @throws NullPointerException if the mapping function is {@code null}
060         */
061        default <R1> Generator<T, R1> map(final Function<? super R, ? extends R1> f) {
062                requireNonNull(f);
063                return cfg -> f.apply(generate(cfg));
064        }
065
066        /**
067         * Standard algorithm for selecting a list of alternative symbols from the
068         * given {@code rule}.
069         *
070         * @param rule the rule to select the alternative from
071         * @param cfg the grammar to select the alternative from
072         * @param index the symbol selection strategy
073         * @param <T> the terminal type
074         * @return the selected symbols
075         * @throws NullPointerException if one of the arguments is {@code null}
076         */
077        static <T> List<Symbol<T>> select(
078                final NonTerminal<T> rule,
079                final Cfg<T> cfg,
080                final SymbolIndex index
081        ) {
082                return cfg.rule(rule)
083                        .map(r -> r.alternatives()
084                                .get(index.next(r, r.alternatives().size()))
085                                .symbols())
086                        .orElse(List.of());
087        }
088
089}