/*
 * Created on Dec 4, 2004
 *
 */
package aima.logic.propositional.visitors;

import java.util.Set;

import aima.logic.propositional.parsing.PLVisitor;
import aima.logic.propositional.parsing.ast.BinarySentence;
import aima.logic.propositional.parsing.ast.FalseSentence;
import aima.logic.propositional.parsing.ast.MultiSentence;
import aima.logic.propositional.parsing.ast.Symbol;
import aima.logic.propositional.parsing.ast.TrueSentence;
import aima.logic.propositional.parsing.ast.UnarySentence;
import aima.util.SetOps;

/**
 * @author Ravi Mohan
 * Super class of Visitors that are "read only" and gather information from an existing parse tree .
 */
public class BasicTraverser implements PLVisitor {

	
	public Object visitSymbol(Symbol s, Object arg) {
		return arg;
	}

	
	public Object visitTrueSentence(TrueSentence ts, Object arg) {
		return arg;
	}

	
	public Object visitFalseSentence(FalseSentence fs, Object arg) {
		return arg;
	}

	
	public Object visitNotSentence(UnarySentence ns, Object arg) {
		Set s =(Set)arg;
		return new SetOps().union(s,(Set)ns.getNegated().accept(this,arg));
	}

	
	public Object visitBinarySentence(BinarySentence bs, Object arg) {
		Set s =(Set)arg;
		Set termunion = new SetOps().union((Set)bs.getFirst().accept(this,arg),(Set)bs.getSecond().accept(this,arg));
		return new SetOps().union(s,termunion);
	}

	
	public Object visitMultiSentence(MultiSentence fs, Object arg) {
		throw new RuntimeException("Can't handle MultiSentence");
	}

}