text: const initialState = Immutable.Map({ counter: 0 });
  
  const actionsMap = {
    increment(state/*, action*/) {
      return state.update('counter', n => n + 1);
    },
    decrement(state/*, action*/) {
      return state.update('counter', n => n - 1);
    }
  };
  
  export default (state = initialState, action) => {
    const reduceFn = actionsMap[action.type];
    if (!reduceFn) return state;
    return reduceFn(state, action);
  };
  