如何在ANTLR语法中切换默认和隐藏令牌通道

Question

我有像这样的解析器规则

if_stmt : IF_T condition THEN_T
          {
           /* Here I would like to change the channel and iterate through the tokens
              from hidden channel*/
           code.....
           /* Here I would like to change it to default token channel again */
          }