require 'continuation'

def reset &ff
  call_stk = []
  last = lambda { |x| call_stk.pop[x] }
  store = lambda { |f| callcc {|cc| call_stk.push(cc); f.call() } }
  shift = lambda do |&f|
    store[ ->{
      k = call_stk.pop
      last[ f.call(->(x){ store[ ->{ last[k[x]] } ] }) ]
    } ]
  end
  store[->{ last[ff[shift]] }]
end

# e.g...

reset do |shift|
  print 'D'
  shift.call do |k|
    k[k]
    print 'E'
    print 'D'
  end
  shift.call do |k|
    print 'E'
    k[k]
    print 'T'
  end
  print 'L'
  shift.call do |k|
    print 'I'
    k[k]
    print 'M'
    k[k]
    print 'I'
  end
end
puts


puts "7+1+1+1=#{reset { |shift| 1+shift.call{|k| k[k[k[7]]] } }}"

lambda do
  k = reset {|shift| 1+shift.call {|kk| kk }}
  puts "#{k[1]}, #{k[k[1]]}"
end.call