title: Why can't I call the reducer directly?
body: <p>I read some introduction blog post on redux and its priciples. I still don't know why the reducer should not be called directly, but by calling an action function with data in the parameter. What is the advantage?</p>
  
  <p>action</p>
  
  <pre><code>export function setPerson(personData) {
    return {
     type: actionTypes.SET_PERSON,
     personData
    };
  }
  </code></pre>