push_pop.ml

let conformToInvariants (queue: 'a queueSuspended): ('a queueSuspended) = 
  let queue = conformToFrontNotSmallerThanRear queue
  in conformToForcedFrontInvariant queue
;;

let push (queue: 'a queueSuspended) (elem: 'a): ('a queueSuspended) =
  match queue with (forcedFront, frontSize, lazyFront, rearSize, rear) ->
    conformToInvariants (
      forcedFront,
      frontSize,
      lazyFront,
      rearSize + 1,
      elem :: rear
    )
;;

let pop (queue: 'a queueSuspended): ('a queueSuspended) = match queue with
  | ([], _, _, _, _) -> raise Empty_queue
  | (head :: forcedFront, frontSize, lazyFront, rearSize, rear) ->
      conformToInvariants (
        forcedFront,
        frontSize - 1,
        lazy (List.tl (Lazy.force lazyFront)),
        rearSize,
        rear
        )
;;