Portion of Itertools module

itertools.nim

iterator cycle*[iterT, returnT](iter: iterT): returnT =
  ## An iterator returning elements from the iterable and saving a 
  ## copy of each. When the iterable is exhausted, return elements 
  ## from the saved copy. Repeats indefinitely.
  ##
  ## Parameters:
  ##   iter: The iterator to cycle through
  var cont: seq[returnT] = @[]
  for element in iter:
    yield element
    cont.add(element)
  while True:
    for element in cont:
      yield element

when isMainModule:
  block:
    var 
      cycleSeq = @[1,2]
      emptySeq = newSeq[int]()
      cycleIterator: cycle[seq[int], int]
    for i in 1..3:
      emptySeq.add(cycleIterator(cycleSeq))
    assert(emptySeq == @[1,2,1,2,1,2])
    echo(repr(emptySeq))