##  From http://gnuu.org/2009/03/21/demystifying-continuations-in-ruby/

require "continuation"

# This use of continuation resembles the "break" operator, breaking out of a block
#   and skipping the code before the "break" and the block's end

def main
  i = 0
  callcc do |cc| # callcc gives us cc (called "label" in the original code), a continuation. 
                 # The do block executes with it as argument; cf. (call/cc (lambda (cc) ..)) 
    puts i
    puts cc
    cc.call    # this call immediately goes to where callcc's value belongs (that value is discarded: 
               #   no expression catches it)
    i = 1      # this future is not reached
  end          
  puts i       # execution comes here next, having discarded the value returned by callcc's block
end

main