https://github.com/narimiran/itertools を参考に。

itertools.nim

iterator chunked*[T](xs: openArray[T], size: int, yieldRest = true): seq[T] =
  var
    i: int
  let
    last = xs.high

  for j in countup(0, xs.len, size + 1):
    i = j
    if i + size > last: break
    yield xs[i .. i + size]
  
  if yieldRest:
    yield xs[i .. ^1]

iterator windowed*[T](xs: openArray[T], size: int): seq[T] =
  for i in 0 .. xs.len - size:
    yield xs[i ..< i + size]

iterator pairwise*[T](xs: openArray[T]): (T, T) =
  for x in xs.windowed(2):
    yield (x[0], x[1])