gistfile1.fs

let groupsOf n (items: seq<_>) =
  use e = items.GetEnumerator()
  let rec loop i acc =
    seq {
      match i, acc, e.MoveNext() with
      | 0, [], _ | _, [], false -> ()
      | _, _, false -> 
        yield seq (List.rev acc)
      | 0, _, true -> 
        yield seq (List.rev acc)
        yield! loop (n - 1) [e.Current]
      | _, _, true ->
        yield! loop (i - 1) (e.Current::acc)
    }
  loop n []