astiterator.java

SRI international 发布的OAA框架软件

package antlr_oaa;

/* ANTLR Translator Generator
 * Project led by Terence Parr at http://www.jGuru.com
 * Software rights: http://www.antlr.org/RIGHTS.html
 *
 * $Id: ASTIterator.java,v 1.1 2002/11/08 17:38:25 agno Exp $
 */

import antlr_oaa.collections.AST;

public class ASTIterator {
    protected AST cursor = null;
    protected AST original = null;


    public ASTIterator(AST t) {
	original = cursor = t;
    }

    /** Is 'sub' a subtree of 't' beginning at the root? */
    public boolean isSubtree(AST t, AST sub) {
	AST sibling;

	// the empty tree is always a subset of any tree.
	if ( sub==null ) {
	    return true;
	}
	
	// if the tree is empty, return true if the subtree template is too. 	
	if ( t==null ) {
	    if ( sub!=null ) return false;
	    return true;
	}	

	// Otherwise, start walking sibling lists.  First mismatch, return false.
	for (sibling=t;
	     sibling!=null&&sub!=null;
	     sibling=sibling.getNextSibling(), sub=sub.getNextSibling())
	    {
		// as a quick optimization, check roots first.
		if ( sibling.getType() != sub.getType() ) return false;
		// if roots match, do full match test on children.
		if ( sibling.getFirstChild()!=null ) {
		    if ( !isSubtree(sibling.getFirstChild(), sub.getFirstChild()) ) return false;
		}	
	    }
	return true;
    }
    /** Find the next subtree with structure and token types equal to
	 * those of 'template'.
	 */
    public AST next(AST template) {
	AST t = null;
	AST sibling = null;
		
	if ( cursor==null ) {	// do nothing if no tree to work on
	    return null;
	}
		
	// Start walking sibling list looking for subtree matches.
	for ( ; cursor!=null; cursor=cursor.getNextSibling())
	    {
		// as a quick optimization, check roots first.
		if ( cursor.getType() == template.getType() ) {
				// if roots match, do full match test on children.
		    if ( cursor.getFirstChild()!=null ) {
			if ( isSubtree(cursor.getFirstChild(), template.getFirstChild()) ) {
			    return cursor;
			}	
		    }
		}	
	    }
	return t;	
    }
}