what if your reducers were generators?

reducers-as-generators.js

// You can defer the side-effect execution in middlewares
const sideEffect = appState => dispatch => localStorage.setItem('counter', appState);

function plainOldReducer(appState) {
  return appState + 1;
}

// Composition simply work
function nestedReducer*(appState, action) {
  if (action === FOO) {
    yield sideEffect(appState);
    return plainOldReducer(appState);
  } else {
    return appState;
  }
}

function rootReducer*(appState = 0, action) {
  return yield* nestedReducer(appState, action);
}