SlotsCreateComponent.re

SlotsCreateComponent.re

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

module Slots: SlotsType = {
  type t('slot, 'nextSlots) = ref(option(('slot, 'nextSlots)));
  let create = () => ref(None);
  let use = (~default, slots: t(_)) =>
    switch (slots^) {
    | None =>
      let slot = default;
      let nextSlots = create();
      slots := Some((slot, nextSlots));
      (slot, nextSlots);
    | Some((slot, nextSlots)) => (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 nextSlots;
  type createElement;
  let createElement: createElement;
  let createSlots: unit => Slots.t(slots, nextSlots);
};

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

/* This fails with:
   Error: The type of this packed module contains variables:
   (module Component with type createElement = one:int -> two:int -> int and type element =
    int and type nextSlots = ('a, 'b) Slots.t and type slots = int)
    */
module IntComponent = (
  val createComponent((render, slots, ~one, ~two) =>
        render(
          {
            let (state, _nextSlots) = useState(3, slots);
            primitive(one + two + state);
          },
        )
      )
);