package prefuse.data.expression;
/**
* Visitor interface for objects that visit each sub-expression of an
* Expression instance, performing some computation or data collection.
*
* @author <a href="http://jheer.org">jeffrey heer</a>
*/
public interface ExpressionVisitor {
/**
* Callback made when visiting a particular expression.
* @param expr the expression currently being visited.
*/
public void visitExpression(Expression expr);
/**
* Callback to signal that the visitor has just descended
* a level in the Expression tree.
*/
public void down();
/**
* Callback to signal that the visitor has just ascended
* a level in the Expression tree.
*/
public void up();
} // end of interface ExpressionVisitor