ReasonReact useReducer hook

Hooks.re

type update('state, 'action) =
  | NoUpdate
  | Update('state)
  | SideEffects(self('state, 'action) => unit)
  | UpdateWithSideEffects('state, self('state, 'action) => unit)
and self('state, 'action) = {
  state: 'state,
  send: 'action => unit,
};

let useReducer = (reducer, initialState) => {
  let extendedReducer = ((state, _), action) => {
    (
      switch (reducer(state, action)) {
      | NoUpdate => state
      | SideEffects(_) => state
      | Update(s) => s
      | UpdateWithSideEffects(s, _) => s
      },
      switch (reducer(state, action)) {
      | SideEffects(f) => Some(f)
      | UpdateWithSideEffects(_, f) => Some(f)
      | Update(_)
      | NoUpdate => None
      },
    );
  };

  let ((state, update), sendState) =
    React.useReducer(extendedReducer, (initialState, None));

  let _ =
    React.useLayoutEffect1(
      () => {
        switch (update) {
        | Some(u) => u({state, send: sendState})
        | None => ()
        };
        None;
      },
      [|update|],
    );

  (state, sendState);
};