public override void PostWalk(IndexExpression node)
 {
 }
 // IndexExpression
 public override bool Walk(IndexExpression node)
 {
     return(false);
 }
 public virtual void PostWalk(IndexExpression node)
 {
 }
 // IndexExpression
 public override bool Walk(IndexExpression node)
 {
     return(Location >= node.StartIndex && Location <= node.EndIndex);
 }
 // IndexExpression
 public virtual bool Walk(IndexExpression node)
 {
     return(true);
 }