Fibonacci numbers and Factorials as iterators

numiter.nim

iterator factorials(k: int): int =
  ## Yields from 0! to k! as an iterator
  var (n, f) = (0, 1)
  yield 1 # for 0!
  while n < k:
    yield f
    n = n + 1; f = f * (n + 1)

iterator fibonacci(cap: int): int =
  ## Yields Fibonacci numbers <= `cap` as an iterator
  var (a, b) = (0, 1)
  while a <= cap:
    yield a
    let tmp = a
    a = b
    b = tmp + b

for f in factorials(10):
  echo f

for f in fibonacci(1000):
  echo f