/*
 * @(#)$Id: OtherExp.java,v 1.4 2001/08/16 02:45:07 Bear Exp $
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */
package com.sun.msv.grammar;

/**
 * Base class for application-specific AGM annotation.
 * 
 * <p>
 * This primitive has no meaning to MSV. For example, the following expression
 * <pre>
 * Expression exp = new OtherExp( pool.createSequence(a,b) );
 * </pre>
 * is treated as if MSV sees the following, OtherExp-less expression:
 * <pre>
 * Expression exp = pool.createSequence(a,b);
 * </pre>
 * 
 * <p>
 * By using this "transparency", application can implement derived classes
 * of <code>OtherExp</code> and add application-specific information to AGM.
 * 
 * <p>
 * For example, you can implement <code>AnnotationInfoExp</code> class that derives
 * <code>OtherExp</code> and introduces "documentation" field.
 * Then you'll write a customized <code>XMLSchemaReader</code> that
 * parses <annotation> tag and mix <code>AnnotationInfoExp</code> into an AGM.
 * Your application can then examine it and do some useful things.
 * 
 * <p>
 * Those application-specific information added through OtherExp are completely
 * ignored by MSV. So the annotated AGM can still be used just like anormal AGM.
 * 
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public class OtherExp extends Expression {
	
	/**
	 * returns the string which will be used by ExpressionPrinter
	 * to print this expression.
	 */
	public String printName() {
		String className = this.getClass().getName();
		int idx = className.lastIndexOf('.');
		if(idx>=0)	className = className.substring(idx+1);
		return className;
	}
	
	/**
	 * child expression.
	 */
	public Expression exp;
	
	public OtherExp() {
		super(null,null);
	}

	public OtherExp( Expression exp ) {
		this();
		this.exp = exp;
	}
	
	public boolean equals( Object o ) {
		return this==o;
	}
	
	protected boolean calcEpsilonReducibility() {
		if(exp==null)
//			// actual expression is not supplied yet.
//			// actual definition of the referenced expression must be supplied
//			// before any computation over the grammar.
//			throw new Error();	// assertion failed.
			return false;
		// this method can be called while parsing a grammar.
		// in that case, epsilon reducibility is just used for approximation.
		// therefore we can safely return false.
		
		return exp.isEpsilonReducible();
	}
	
	// derived class must be able to behave as a ReferenceExp
	public final Object visit( ExpressionVisitor visitor )				{ return visitor.onOther(this); }
	public final Expression visit( ExpressionVisitorExpression visitor ){ return visitor.onOther(this); }
	public final boolean visit( ExpressionVisitorBoolean visitor )		{ return visitor.onOther(this); }
	public final void visit( ExpressionVisitorVoid visitor )			{ visitor.onOther(this); }
}