public virtual void Visit (ExpressionNode node)
		{
		}
			public override void Visit (ExpressionNode node)
			{
				parent.Expressions.Add (node);
			}
		public override void Visit (ExpressionNode node)
		{
			debugString.Append ('\t', indent);
			debugString.Append (node.ToString ());
			debugString.AppendLine ();
		}