@lexer::members
{
  private boolean flag;

  public void setFlag(boolean flag)
  {
    this.flag = flag;
  }
}


identifier1 :
 ID1
 ;

identifier2 :
ID2
;


ID1 : (CHARS) *;


ID2 : (CHARS | ({flag}? '_'))* ;


fragment CHARS
:
  ('a' .. 'z')
;

ANTLRStringStream in = new ANTLRStringStream("abcabde");
    IdTestLexer lexer = new IdTestLexer(in);
    lexer.setFlag(true);
    CommonTokenStream tokens = new CommonTokenStream(lexer);
    IdTestParser parser = new IdTestParser(tokens);
    parser.identifier2();