&gt; I feel like I&#x27;ve progressed in my understanding of those concepts by reading the post<p>You might have progressed but I would guess that you actually haven&#x27;t, because it was a very poor explanation.  How is IO a container?  How is State a container?  Sure, you can stretch the definition so that container means &quot;Functor&quot; but then you&#x27;ve made a circular definition.  Containers are <i>examples</i> of functors.  They do not exhaust all possible functors.<p>EDIT: What yummyfajitas said: <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11553828" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11553828</a>