index.ducks.js

import { combineReducers } from 'redux';

// Import subreducers
import editReducer from './edit/ducks';
import detailsReducer from './details/ducks';
import listReducer from './list/ducks';

const initialState = {
  // common stuff here
};

function reducer(state = initialState, action = {}) {
  switch (action.type) {
    case 'SOMETHING':
      ...
    default:
      return state;
  }
}

export default combineReducers({
  common: reducer,
  edit: editReducer,
  list: listReducer,
  details: detailsReducer,
});