title: What's the point of the `select` effect in redux-saga?
body: <p>As redux-saga describes itself as </p>
  
  <blockquote>
    <p>a library that aims to make application <code>side effects</code> (i.e.
    asynchronous things like data fetching and impure things like
    accessing the browser cache) easier to manage.</p>
  </blockquote>
  
  <p>The <code>select</code> effect is just used to <code>get a slice of the current Store's state</code>. It doesn't produce any side effect at all (no I/O operation, no mutation,etc). It's just a purely functional operation. Why a purely functional operation was designed to be an effect ? </p>