01 /*
02 * Java Genetic Algorithm Library (jenetics-7.1.2).
03 * Copyright (c) 2007-2023 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.grammar;
21
22 import static java.util.Objects.requireNonNull;
23
24 import java.util.List;
25 import java.util.function.Function;
26
27 import io.jenetics.ext.grammar.Cfg.NonTerminal;
28 import io.jenetics.ext.grammar.Cfg.Symbol;
29
30 /**
31 * Generator interface for generating <em>sentences</em>/<em>derivation trees</em>
32 * from a given grammar.
33 *
34 * @param <T> the terminal token type of the grammar
35 * @param <R> the result type of the generator
36 *
37 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
38 * @since 7.1
39 * @version 7.1
40 */
41 @FunctionalInterface
42 public interface Generator<T, R> {
43
44 /**
45 * Generates a new sentence from the given grammar. If the generation of the
46 * sentence fails, an empty list is returned.
47 *
48 * @param cfg the generating grammar
49 * @return a newly created result
50 */
51 R generate(final Cfg<? extends T> cfg);
52
53 /**
54 * Maps the generated result from type {@code R} to type {@code R1}.
55 *
56 * @param f the mapping function
57 * @param <R1> the target type
58 * @return a new generator with target type {@code R1}
59 * @throws NullPointerException if the mapping function is {@code null}
60 */
61 default <R1> Generator<T, R1> map(final Function<? super R, ? extends R1> f) {
62 requireNonNull(f);
63 return cfg -> f.apply(generate(cfg));
64 }
65
66 /**
67 * Standard algorithm for selecting a list of alternative symbols from the
68 * given {@code rule}.
69 *
70 * @param rule the rule to select the alternative from
71 * @param cfg the grammar to select the alternative from
72 * @param index the symbol selection strategy
73 * @param <T> the terminal type
74 * @return the selected symbols
75 * @throws NullPointerException if one of the arguments is {@code null}
76 */
77 static <T> List<Symbol<T>> select(
78 final NonTerminal<T> rule,
79 final Cfg<T> cfg,
80 final SymbolIndex index
81 ) {
82 return cfg.rule(rule)
83 .map(r -> r.alternatives()
84 .get(index.next(r, r.alternatives().size()))
85 .symbols())
86 .orElse(List.of());
87 }
88
89 }
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