cycleWithoutNull.ml

(* Doubly linked list node *)
type 'a dlln = { mutable data : 'a ;
                 mutable prev : 'a dlln ;
                 mutable next : 'a dlln }

(* Look ma, a cycle can be initialized without any NULL pointers! *)
let rec singleton : int dlln =
  { data = 0 ;
    prev = singleton ;
    next = singleton }
;;

The fields are mutable so that it's morally closer to C. In OCaml, such definitions require no laziness, implicit or explicit. No function abstractions/applications are required.