module type SlotsType = {
  type t('slot, 'nextSlots);
  let create: unit => t('slot, 'nextSlots);
  let use:
    (
      ~default: 'slot,
      (('slot, t('slot2, 'nextSlots))) => 'c,
      t('slot, t('slot2, 'nextSlots))
    ) =>
    ('c, 'slot);
};

module Slots: SlotsType = {
  type t('slot, 'nextSlots) = option(('slot, 'nextSlots));
  let create = () => None;
  let use = (~default, continuation, slots: t(_)) =>
    switch (slots) {
    | None =>
      let slot = default;
      let nextSlots = create();
      let next = (slot, nextSlots);
      (continuation(next), slot);
    | Some((slot, nextSlots)) =>
      let next = (slot, nextSlots);
      (continuation(next), slot);
    };
};

type element = int;
type hook('slot, 'nextSlots) = (element, Slots.t('slot, 'nextSlots));

let useState = (initial, slots) => slots |> Slots.use(~default=initial);

let primitive: 'a => 'a = x => x;

module type Component = {
  type element;
  type slots;
  type createElement;
  let createElement: createElement;
  let createSlots: unit => Slots.t(slots, _);
};

let createComponent =
    (type c, type e, type s, create: ((e, s) => (e, s), Slots.t(s, _)) => c)
    : (module Component with
         type createElement = c and type element = e and type slots = s) =>
  (module
   {
     type element = e;
     type slots = s;
     type createElement = c;
     let createSlots = () => Slots.create();
     let createElement =
       create((element, slot) => (element, slot), createSlots());
   });

module MyComponent = (
  val createComponent((render, slots, ~one, ~two) =>
        render(
          useState(
            3,
            ((state, slots)) =>
              useState(
                "3",
                ((stateStr, _slots)) =>
                  primitive(one + two + state + int_of_string(stateStr)),
                slots,
              ),
            slots,
          ),
        )
      )
);

let test = (slots) => 
  useState(
    3,
    ((state, slots)) =>
      useState(
        "3",
        ((stateStr, _slots)) => state + int_of_string(stateStr),
        slots,
      ),
    slots,
  );

let (slot, element) = test(Slots.create());