anchor.diff:  natural_number : POSITIVE_INT | ZERO;
   //四则运算符
   arithmetic_op : PLUS | MINUS | STAR | SLASH;
  +//二元位运算
  +bitwise_op : BITWISE_AND | BITWISE_OR | BITWISE_EXCLUSIVE_OR;
  +//二元运算符
  +binary_op : arithmetic_op | bitwise_op | EXPONENITIATION;
  +//一元运算符
  +unary_op : BITWISE_COMPLEMENT;
  +//数字
  +bit_number : unary_op? natural_number;
   //关系运算符(comparison predicates)
   relation_op : LESS_THAN | LEQ | GREATER_THAN | GEQ | EQUAL | DOUBLE_EQUAL | NEQ;
   
  
positive.code: //变量
  VAR : [A-Z][a-zA-Z0-9_]*;
  
  //加号
  PLUS : '+';
  //减号、经典否定关键字
  
negative.code: simple_arithmetic_expr :
      integer |
      (MINUS)? VAR |
      (integer | (MINUS)? VAR) (binary_op (bit_number | VAR))* ;
  
  //四则运算算术表达式，加括号
  simple_arithmetic_expr2 :
  