def unfold(fn, seed):
  def fn_generator(val):
    while True: 
      val = fn(val[1])
      if val == False: break
      yield val[0]
  return [i for i in fn_generator([None, seed])]
  
  
EXAMPLES
f = lambda n: False if n > 50 else [-n, n + 10]
unfold(f, 10) # [-10, -20, -30, -40, -50]