配列にためる手間なしenum_for ref: https://qiita.com/hanachin_/items/134000befc7f5fdce94c

file0.txt

def 動物API
  @動物API ||= Object.new
end

def 動物API.page(page)
  {
    1 => ["鶏"],
    2 => ["豚"],
    3 => ["牛"]
  }[page] || []
end

def いろんな肉
  page = 1
  肉 = []
  while true
    animals = 動物API.page(page)

    break if animals.empty?

    肉 += animals
    page += 1
  end
  肉
end

いろんな肉.each do |肉|
  puts 肉
end
# 鶏
# 豚
# 牛

file1.txt

def 動物API
  @動物API ||= Object.new
end

def 動物API.page(page)
  {
    1 => ["鶏"],
    2 => ["豚"],
    3 => ["牛"]
  }[page] || []
end

def each_いろんな肉
  page = 1
  while true
    animals = 動物API.page(page)

    break if animals.empty?

    animals.each {|a| yield a }
    page += 1
  end
end

each_いろんな肉 do |肉|
  puts 肉
end
# 鶏
# 豚
# 牛

file2.txt

def 動物API
  @動物API ||= Object.new
end

def 動物API.page(page)
  {
    1 => ["鶏"],
    2 => ["豚"],
    3 => ["牛"]
  }[page] || []
end

def each_いろんな肉
  page = 1
  while true
    animals = 動物API.page(page)

    break if animals.empty?

    animals.each {|a| yield a }
    page += 1
  end
end

def いろんな肉
  enum_for(:each_いろんな肉).to_a
end

puts いろんな肉.join("と") + "を全部焼いたもの"
# 鶏と豚と牛を全部焼いたもの