def binary(left, operator, right)
      parentheses do
        left.visit(self)
        append(" #{operator} ")
        right.visit(self)
      end
    end
def binary(left, operator, right)
      parentheses do
        left.visit(self)
        append(" #{operator} ")
        right.visit(self)
      end
    end
Emit binary

 @param [Node] left
 @param [Symbol] operator
 @param [Node] right

 @return [self]

 @api private