lazy_enumeration.rb

input = 1.upto 10

lazy = input.lazy.map { |v|
  result = v * 2
  p times_2: result
  result
}.each_slice(2).map { |v1, v2|
  result = v1 + v2
  p add_pairs: result
  result
}

p lazy.to_a

lazy_enumeration_expanded.rb

input = 1.upto 10

times_2 = Enumerator.new do |out|
  loop do
    v = input.next

    result = v * 2

    p times_2: result

    out << result
  end
end

add_pairs = Enumerator.new do |out|
  loop do
    v1 = times_2.next
    v2 = times_2.next

    result = v1 + v2

    p add_pairs: result

    out << result
  end
end

p add_pairs.to_a

Output

{:times_2=>2}
{:times_2=>4}
{:add_pairs=>6}
{:times_2=>6}
{:times_2=>8}
{:add_pairs=>14}
{:times_2=>10}
{:times_2=>12}
{:add_pairs=>22}
{:times_2=>14}
{:times_2=>16}
{:add_pairs=>30}
{:times_2=>18}
{:times_2=>20}
{:add_pairs=>38}
[6, 14, 22, 30, 38]