# File lib/sass/script/unary_operation.rb, line 48
    def _perform(environment)
      operator = "unary_#{@operator}"
      literal = @operand.perform(environment)
      literal.send(operator)
    rescue NoMethodError => e
      raise e unless e.name.to_s == operator.to_s
      raise Sass::SyntaxError.new("Undefined unary operation: \"#{@operator} #{literal}\".")
    end