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AIMA-Java Core Algorithms from the book Artificial Intelligence a Modern Approach 3rd Ed.
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package aima.core.logic.propositional.parsing.ast;
/**
* Artificial Intelligence A Modern Approach (3rd Edition): page 244.
*
* Complex Sentence: are constructed from simpler sentences, using
* parentheses (and square brackets) and logical connectives.
*
* @author Ciaran O'Reilly
* @author Ravi Mohan
*/
public class ComplexSentence extends Sentence {
private Connective connective;
private Sentence[] simplerSentences;
// Lazy initialize these values.
private int cachedHashCode = -1;
private String cachedConcreteSyntax = null;
/**
* Constructor.
*
* @param connective
* the complex sentence's connective.
* @param sentences
* the simpler sentences making up the complex sentence.
*/
public ComplexSentence(Connective connective, Sentence... sentences) {
// Assertion checks
assertLegalArguments(connective, sentences);
this.connective = connective;
simplerSentences = new Sentence[sentences.length];
for (int i = 0; i < sentences.length; i++) {
simplerSentences[i] = sentences[i];
}
}
/**
* Convenience constructor for binary sentences.
*
* @param sentenceL
* the left hand sentence.
* @param binaryConnective
* the binary connective.
* @param sentenceR
* the right hand sentence.
*/
public ComplexSentence(Sentence sentenceL, Connective binaryConnective, Sentence sentenceR) {
this(binaryConnective, sentenceL, sentenceR);
}
@Override
public Connective getConnective() {
return connective;
}
@Override
public int getNumberSimplerSentences() {
return simplerSentences.length;
}
@Override
public Sentence getSimplerSentence(int offset) {
return simplerSentences[offset];
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if ((o == null) || (this.getClass() != o.getClass())) {
return false;
}
boolean result = false;
ComplexSentence other = (ComplexSentence) o;
if (other.hashCode() == this.hashCode()) {
if (other.getConnective().equals(this.getConnective())
&& other.getNumberSimplerSentences() == this
.getNumberSimplerSentences()) {
// connective and # of simpler sentences match
// assume match and then test each simpler sentence
result = true;
for (int i = 0; i < this.getNumberSimplerSentences(); i++) {
if (!other.getSimplerSentence(i).equals(
this.getSimplerSentence(i))) {
result = false;
break;
}
}
}
}
return result;
}
@Override
public int hashCode() {
if (cachedHashCode == -1) {
cachedHashCode = 17 * getConnective().hashCode();
for (Sentence s : simplerSentences) {
cachedHashCode = (cachedHashCode * 37) + s.hashCode();
}
}
return cachedHashCode;
}
@Override
public String toString() {
if (cachedConcreteSyntax == null) {
if (isUnarySentence()) {
cachedConcreteSyntax = getConnective()
+ bracketSentenceIfNecessary(getConnective(), getSimplerSentence(0));
} else if (isBinarySentence()) {
cachedConcreteSyntax = bracketSentenceIfNecessary(getConnective(), getSimplerSentence(0))
+ " "
+ getConnective()
+ " "
+ bracketSentenceIfNecessary(getConnective(), getSimplerSentence(1));
}
}
return cachedConcreteSyntax;
}
//
// PRIVATE
//
private void assertLegalArguments(Connective connective, Sentence...sentences) {
if (connective == null) {
throw new IllegalArgumentException("Connective must be specified.");
}
if (sentences == null) {
throw new IllegalArgumentException("> 0 simpler sentences must be specified.");
}
if (connective == Connective.NOT) {
if (sentences.length != 1) {
throw new IllegalArgumentException("A not (~) complex sentence only take 1 simpler sentence not "+sentences.length);
}
}
else {
if (sentences.length != 2) {
throw new IllegalArgumentException("Connective is binary ("+connective+") but only "+sentences.length + " simpler sentences provided");
}
}
}
}