io.jenetics.ext.grammar.SentenceGenerator Maven / Gradle / Ivy
/*
* 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.grammar;
import static java.util.Objects.requireNonNull;
import static java.util.stream.Collectors.joining;
import static io.jenetics.ext.grammar.SentenceGenerator.Expansion.LEFT_MOST;
import java.util.ArrayList;
import java.util.List;
import java.util.ListIterator;
import io.jenetics.ext.grammar.Cfg.NonTerminal;
import io.jenetics.ext.grammar.Cfg.Symbol;
import io.jenetics.ext.grammar.Cfg.Terminal;
/**
* Standard implementation of a sentence generator. The generator can generate
* sentences by expanding the grammar in a {@link Expansion#LEFT_MOST} or
* {@link Expansion#LEFT_TO_RIGHT} order.
*
* The following code snippet shows how to create a random sentence from a
* given grammar:
* {@snippet lang="java":
* final Cfg cfg = Bnf.parse("""
* ::= ( ) | | | ( , )
* ::= FUN1 | FUN2
* ::= | |
* ::= + | - | * | /
* ::= x | y
* ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
* """
* );
*
* final var random = RandomGenerator.of("L64X256MixRandom");
* final var generator = new SentenceGenerator(
* SymbolIndex.of(random),
* 1_000
* );
* final List> sentence = generator.generate(cfg);
* final String string = sentence.stream()
* .map(Symbol::name)
* .collect(Collectors.joining());
*
* System.out.println(string);
* }
* Some sample output:
* {@code
* > ((x-FUN1(5,5))+8)
* > (FUN2(y,5)-FUN2(0,x))
* > x
* > FUN2(x,x)
* > 5
* > FUN2(y,FUN2((FUN1(5,FUN1(y,2))*9),y))
* > ((FUN1(x,5)*9)*(x/(y*FUN2(x,y))))
* > (9-(y*(x+x)))
* >
* }
*
* @see DerivationTreeGenerator
*
* @author Franz Wilhelmstötter
* @since 7.1
* @version 7.1
*/
public final class SentenceGenerator
implements Generator>>
{
/**
* Defines the expansion strategy used when generating the sentences.
*/
public enum Expansion {
/**
* The symbol replacement always starting from the leftmost nonterminal
* as described in
* Grammatical Evolution.
*/
LEFT_MOST,
/**
* The symbol replacement is performed from left to right and is repeated
* until all non-terminal symbols have been expanded.
*/
LEFT_TO_RIGHT;
}
private final SymbolIndex _index;
private final Expansion _expansion;
private final int _limit;
/**
* Create a new sentence generator from the given parameters.
*
* @param index the symbol index function used for generating the sentences
* @param expansion the sentence generation strategy to use for generating
* the sentences
* @param limit the maximal allowed sentence length. If the generated
* sentence exceeds this length, the generation is interrupted and
* an empty sentence (empty list) is returned.
*/
public SentenceGenerator(
final SymbolIndex index,
final Expansion expansion,
final int limit
) {
_index = requireNonNull(index);
_expansion = requireNonNull(expansion);
_limit = limit;
}
/**
* Create a new sentence generator from the given parameters.
*
* @param index the symbol index function used for generating the sentences
* @param limit the maximal allowed sentence length. If the generated
* sentence exceeds this length, the generation is interrupted and
* an empty sentence (empty list) is returned.
*/
public SentenceGenerator(
final SymbolIndex index,
final int limit
) {
this(index, LEFT_MOST, limit);
}
/**
* Generates a new sentence from the given grammar, cfg.
*
* @param cfg the generating grammar
* @return a newly created terminal list (sentence), or an empty list if
* the length of the sentence exceeds the defined sentence limit
*/
@Override
public List> generate(final Cfg cfg) {
final var sentence = new ArrayList>();
generate(Cfg.upcast(cfg), sentence);
// The 'generate' step guarantees that the list only
// contains terminal symbols. So this cast is safe.
@SuppressWarnings("unchecked")
final var result = (List>)(Object)sentence;
return List.copyOf(result);
}
void generate(final Cfg cfg, final List> symbols) {
symbols.add(cfg.start());
boolean proceed;
do {
proceed = false;
final ListIterator> sit = symbols.listIterator();
while (sit.hasNext() &&
(_expansion == Expansion.LEFT_TO_RIGHT || !proceed))
{
if (sit.next() instanceof NonTerminal nt) {
sit.remove();
Generator.select(nt, cfg, _index).forEach(sit::add);
proceed = true;
}
}
if (symbols.size() > _limit) {
symbols.clear();
proceed = false;
}
} while (proceed);
}
/**
* Converts a list of symbols to a string, by concatenating the names of
* the given symbols.
*
* @param sentence the symbol list to covert
* @return the converted sentences
*/
public static String toString(final List> sentence) {
return sentence.stream().map(Symbol::name).collect(joining());
}
}