lensnest

foo.re

// Nesting
type action =
 | Auth(Auth.action)

let reduce = ...
 | Auth(action) =>
      nestByLens(
        Auth.reduce,
        stateAuthLens,
        subaction => Auth(subaction),
        state,
        action,
      )

// nestByLens
let nestByLens:
  type substate subaction state action.
    (
      (substate, subaction) => update(subaction, substate),
      Lens.t(state, substate),
      subaction => action,
      state,
      subaction
    ) =>
    update(action, state) =
  (reduce, lens, liftAction, state, subaction) => {
    let substate = Lens.view(lens, state);
    let result = reduce(substate, subaction);

    let liftSideEffects =
      Array.map((fn, {dispatch, state}) => {
        let subdispatch = subAction => liftAction(subAction) |> dispatch;
        let substate = Lens.view(lens, state);

        fn({
          dispatch: subdispatch,
          state: substate,
        });
      });

    switch (result) {
    | Update(substate) => Update(Lens.set(lens, substate, state))
    | UpdateWithSideEffects(substate, sideEffects) =>
      UpdateWithSideEffects(
        Lens.set(lens, substate, state),
        liftSideEffects(sideEffects),
      )
    | SideEffects(xs) => SideEffects(liftSideEffects(xs))
    | NoUpdate => NoUpdate
    };
  };