send :fibo, n:5
send :if, f:1
recv :fibo do |n|
  send :gt, n:n
  send :dec1, n:n
  send :dec2, n:n
  send :sum, a:n  # if tagged
  send :sum, b:n  # if tagged right
end
recv :if do |c, t, f|
  if c
    send :fibo, n:t
  else
    send :fibo, n:f
  end
end
recv :sum do |a, b|
  send :if, t:(a + b)
end
recv :dec1 do |n|
  send :fibo, n:(n-1)
end
recv :dec2 do |c|
  send :fibo, n:(n-2)
end