type Iterator = iterator(): int

proc `^`*(base: Natural; exp: Natural): int =
  var (base, exp) = (base, exp)
  result = 1
  while exp != 0:
    if (exp and 1) != 0:
      result *= base
    exp = exp shr 1
    base *= base

proc next(s: Iterator): int =
  for n in s(): return n

proc powers(m: Natural): Iterator =
  iterator it(): int {.closure.} =
    for n in 0 ..< int.high:
      yield n ^ m
  result = it

iterator filtered(s1, s2: Iterator): int =
  var v = next(s1)
  var f = next(s2)
  while true:
    if v > f:
      f = next(s2)
      continue
    elif v < f:
      yield v
    v = next(s1)

var
  squares = powers(2)
  cubes = powers(3)
  i = 1
for x in filtered(squares, cubes):
  if i > 20: echo x
  if i >= 30: break
  inc i