Type definitions

[ambientlight]

Adds type definitions discussed in #24, however with difference in following definitions:

type storeCreator('action, 'origin, 'state) =
  (
    ~reducer: reducer('action, 'origin),
    ~preloadedState: 'state,
    ~enhancer: middleware('action, 'state)=?,
    unit
  ) =>
  store('action, 'state);

type storeEnhancer('action, 'origin, 'state) =
  storeCreator('action, 'origin, 'state) =>
  storeCreator('action, 'origin, 'state);

type applyMiddleware('action, 'origin, 'state) =
  middleware('action, 'state) => storeEnhancer('action, 'origin, 'state);

Additional type parameter 'origin accounts for the scenario when storeEnhancer applies composition (decorates original store with higher level state and reducer - hope my wording is correct here), where real-world example looks the following way:

Enhancer to wrap ReactReason router:

let enhancer = (storeCreator: storeCreator('action, 'origin, 'state)) => (~reducer, ~preloadedState, ~enhancer=?, ()) => {
  let routerReducer = (state, action) => 
    switch(action){
    | `RouterLocationChanged(route: ReasonReact.Router.url) => { ...state, route }
    | _ => {
      ...state,
      state: reducer(state.state, action)
    }};
  
  let interceptPushRoute = (store, next, action) => 
    switch(action, enhancer){
    | (`RouterPushRoute(path), _) => ReasonReact.Router.push(path);
    | (_, Some(enhancer)) => enhancer(store, next, action)
    | (_, None) => next(action)
    };
  
  let store = storeCreator(~reducer=routerReducer, ~preloadedState, ~enhancer=interceptPushRoute, ());
  let _watcherId = ReasonReact.Router.watchUrl(url => Reductive.Store.dispatch(store, `RouterLocationChanged(url)));
  store
};

which is used in store defined like:

let storeCreator = devToolsEnhancer @@ ReductiveRouter.enhancer @@ Reductive.Store.create;
let store = storeCreator(
  ~reducer=appReducer,
  ~preloadedState={
    route: {
      path: [],
      hash: "",
      search: ""
    },
    state: {
      counter: 0, 
      content: ""
    },
  },
  (),
);

storeCreator in this case is passed with an original reducer - sub-reducer in our resulting decorated store.

[MargaretKrutikova]

Was just planning to look into this, is the code in the PR no longer necessary?

[ambientlight]

I no longer think that breakdown for 'action, 'origin, 'state is a good idea. Pull request was created when I got originally confused when my storeEnhancer composition was applied in an opposite to expected way, and type system as expected has complained on this. by that time I forgot about this pr, and basically just saw it.