title: check previous/left token in lexer
body: <p>how can I find the previous/left token in lexer<br>
  for example  </p>
  
  <pre><code>lexer grammar TLexer;
  
  ID     : [a-zA-Z] [a-zA-Z0-9]*;
  CARET  : '^';
  RTN    : {someCond1}? CARET ID; // CARET not include this token
  GLB    : {someCond2}? CARET ID; // CARET not include this token
  </code></pre>
  
  <p>etc</p>