SlotsCreateContainsVariables.re

SlotsCreateContainsVariables.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;
type element = int;

module type Component = {
  type slots;
  type createElement;
  let createElement: createElement;
};

let createComponent =
    (
      type c,
      type s,
      create:
        (
          (
            Slots.t(s, _) => element,
            ~children: list(element),
            Slots.t(s, _)
          ) =>
          element
        ) =>
        c,
    )
    : (module Component with type createElement = c and type slots = s) =>
  (module
   {
     type slots = s;
     type createElement = c;
     let createElement =
       create((userRender, ~children) => {
         ignore(children);
         slots => {
           let childElement = userRender(slots);
           childElement;
         };
       });
   });

/* Fails with: "Error: The type of this packed module contains variables" */
module MyComponent = (
  val createComponent((render, ~one, ~two, ~children, ()) =>
        render(
          slots => {
            let (state, slots) = useState(3, slots);
            let (stateStr, _slots) = useState("3", slots);
            primitive(one + two + state + int_of_string(stateStr));
          },
          ~children,
        )
      )
);

let comp = <MyComponent one=1 two=2 />;