HooksHeterogenousList.re

type t('list, 'last) =
  | []: t('a, 'a)
  | ::('a, t('l, 't)): t('a => 'l, 't);

let rec (@):
  type start mid rest. (t(start, mid => rest), mid) => t(start, rest) =
  (l, r) =>
    switch (l) {
    | [] => [r]
    | [a, ...q] => [a, ...q @ r]
    };

let split: type a b. t(a => b, unit) => (a, t(b, unit)) =
  fun
  | [a, ...q] => (a, q)

let use:
  type a value start rest.
    (option(t(value => a, unit)), value, t(start, value => rest)) =>
    (value, t(start, rest), option(t(a, unit))) =
  (hooks, default, nextHooks) =>
    switch (hooks) {
    | Some(hooks) =>
      let (value, rest) = split(hooks);
      (value, nextHooks @ value, Some(rest));
    | None => (default, nextHooks @ default, None)
    };

{
  let initl = ["a", 0];
  let l = Some(initl);
  let nextl = [];
  let (_da_value, nextl, l) = use(l, "1", nextl);
  let (_da_value, nextl, _) = use(l, 2, nextl);
  let res = string_of_bool(initl == nextl); /* true */
  print_endline(res);
};