Модуль с одной публичной функцией, которая call

group_page_numbers.rb

module Concerns
  module PrintOrder
    module GroupPageNumbers
      def sequent_grouping(array)
        begin_group, prev_value, result = nil, nil, []

        array.sort.each_with_index do |item, index|
          if index.zero?
            begin_group, prev_value = index, item
          elsif prev_value.succ != item
            group = array[begin_group...index]
            result << ((yield group) || group)
            begin_group = index
          end

          if index == array.size - 1
            group = array[begin_group..index]
            result << ((yield group) || group)
          end

          prev_value = item
        end

        result
      end

      def compress_pages(array)
        sequent_grouping(array) do |arr|
          arr.size == 1 ? arr.first : "#{arr[0]}-#{arr[-1]}"
        end.join(',')
      end

      alias call compress_pages

      module_function :call
    end
  end
end

Вызывать примерно так же как и метод:

Concerns::PrintOrder::GroupPageNumbers.(array)