gistfile1.rb

#Enumerator.new {|y| y.yield 1}.each {break}

class Enumerator
  def initialize(&b)
    @g = Generator.new(&b)
  end

  def each
    @g.each do |x|
      yield x
    end
  end
end

class Generator
  def initialize(&b)
    @b = b
  end

  def each(&b)
    y = Yielder.new(&b)
    @b.call(y)
  end
end

class Yielder
  def initialize(&b)
    @b = b
  end

  def yield(x)
    @b.call(x)
  end
end

Enumerator.new {|y| y.yield 1}.each {break}