code: def accept_operator(self, precedence):
          
          match = grammar.infix(self.tokens)
          if not match:
              return
  
          if match.operator.precedence < precedence:
              return
  
          # The next thing is an operator that we want. Now match it for real.
          return self.tokens.accept(grammar.infix)
docs: Accept the next binary operator only if it's of higher precedence.