Reducer With Side Effects

ReducerWithEffects.re

module ReducerWithEffects = {
  type actionWrapper('state, 'action) =
    | Update('state)
    | SideEffect(('action => unit) => unit)
    | UpdateWithSideEffect('state, ('action => unit) => unit)
    | NoUpdate;

  type stateWrapper('state, 'action) = {
    state: 'state,
    effect: option(('action => unit) => unit),
  };

  let reducerWrapper = (state, action) => {
    switch (action) {
    | Update(s) => {state: s, effect: None}
    | SideEffect(effect) => {...state, effect: Some(effect)}
    | UpdateWithSideEffect(state, effect) => {state, effect: Some(effect)}
    | NoUpdate => {...state, effect: None}
    };
  };

  let useReducerWithEffects =
      (
        parentReducer: ('state, 'action) => actionWrapper('state, 'action),
        initialState,
      ) => {
    let (state, mainDispatch) =
      React.useReducer(reducerWrapper, {state: initialState, effect: None});

    let dispatch: 'action => unit =
      action => {
        let action = parentReducer(state.state, action);
        mainDispatch(action);
      };

    React.useEffect1(
      () => {
        switch (state.effect) {
        | Some(fn) => fn(dispatch)
        | None => ()
        };
        None;
      },
      [|state.effect|],
    );

    (state.state, dispatch);
  };
};