public void ToSource(StringBuilder sb)
 {
     if (token.ID == TokenID.Invalid)
     {
         expression.ToSource(sb);
     }
     else
     {
         sb.Append(token.ID.ToString().ToLower());
     }
 }
        public override void ToSource(StringBuilder sb)
        {
            sb.Append("using ");

            if (IsAlias)
            {
                aliasName.ToSource(sb);
                sb.Append(" = ");
            }

            // target
            target.ToSource(sb);

            sb.Append(";");
            NewLine(sb);
        }