goal.rb

#!/usr/bin/env ruby
require 'continuation'

def newG(prefix = 'g')
  proc do |tail = nil|
    str = prefix
    cont = nil
    callcc{ |cc| cont = cc }
    if tail == nil
      str += 'o'
      newG(str)
    else
      str += tail
    end
  end
end

g = newG()
puts g.call().call().call('al')

Good point, it's not.