For articles about Lipa #1

calc_tree.rb

require "lipa"

store = Lipa::Tree.new :store do 
  kind :category, :for => :node do
    unit_count Proc.new {
      count = 0
      children.values.each do |u|  
        count += u.count if u.kind == "unit"
      end

      count
    }

    total_cost Proc.new {
      total_cost = 0
      children.values.each do |u|  
        total_cost += u.count * u.cost if u.kind == "unit"
      end

      total_cost
    }
  end

  kind :unit, :for => :node do
    count 0
    cost 0.0
    with_nds  Proc.new{cost * 1.18}
  end

  category :electorinics do 
    category :video do 
      with :label => "Sony" do
        unit :tv_1 do 
          count       231
          part_number "123-567-a"
          cost         100.0
        end

        unit :tv_2 do 
          count       27
          part_number "123-567-b"
          cost        199.0
        end
      end

      unit :tv_3 do 
        count       98
        part_number "123-567-c"
        cost        299.0
        label       "Samsung"
      end
    end

    category :audio do 
      unit :player_1 do 
        count       193
        part_number "123-567-d"
        cost        99.0
        label       "Apple"
      end
    end
  end
end

puts store.electorinics.video.unit_count
puts store.electorinics.video.total_cost

kind_tree.rb

require "lipa"

store = Lipa::Tree.new :store do 
  kind :category, :for => :node
  kind :unit, :for => :node

  category :electorinics do 
    category :video do 
      with :label => "Sony" do
        unit :tv_1 do 
          count       231
          part_number "123-567-a"
          cost         100.0
        end

        unit :tv_2 do 
          count       27
          part_number "123-567-b"
          cost        199.0
        end
      end

      unit :tv_3 do 
        count       98
        part_number "123-567-c"
        cost        299.0
        label       "Samsung"
      end
    end

    category :audio do 
      unit :player_1 do 
        count       193
        part_number "123-567-d"
        cost        99.0
        label       "Apple"
      end
    end
  end
end

puts store.electorinics.video.tv_1.label
puts store.electorinics.audio.player_1.cost
puts store.electorinics.video.name

simplee_tree.rb

require "lipa"

store = Lipa::Tree.new :store do 
  node :electorinics do 
    node :video do 
      node :tv_1 do 
        count       231
        part_number "123-567-a"
        cost         100.0
        label       "Sony"
      end

      node :tv_2 do 
        count       27
        part_number "123-567-b"
        cost        199.0
        label       "Sony"
      end
        
      node :tv_3 do 
        count       98
        part_number "123-567-c"
        cost        299.0
        label       "Samsung"
      end
    end

    node :audio do 
      node :player_1 do 
        count       193
        part_number "123-567-d"
        cost        99.0
        label       "Apple"
      end
    end
  end
end

puts store.electorinics.video.tv_1.label
puts store.electorinics.audio.player_1.cost