While Type theory in general is fundamental for people who implement languages (and too often we see the result of the lack of knowledge of type theory in the implementation of main stream languages, and no, I&#x27;m not talking about PHP here), most developers just want to get an idea of what all that stuff is about. Most developers will never use functors but Monads have interesting applications, like Futures (i.e. Promises).<p>It&#x27;s easy to understand with this article that the usual notion of type (int32,char*,...) is just a subset of what types actually are. (T) -&gt; T is also a type. And if most developers can remember that, well, that&#x27;s a good thing.