Did you read the entire post? Functions were only the first example to introduce the reader to the basic idea of associativity and identity. The post then discusses the Kleisli category and the category of coroutine pipelines.
I did read the entire post. Isomorphisms and homomorphisms between groups also obey associativity, identity, can be composed etc - but there is no point to talking about the 'category of groups', as opposed to, simply, Group theory unless I somewhere use the fact that it's a category, in say, talking about the topological spaces, and the fundamental group etc.
Did you read my comment? I claim that because something is associative and has identity, concepts clarified and used in the 19th century, is not sufficient motivation to bring about category theory. It's not used for anything in this article.
You are correct, but it seems a bit much to take the author to task about this. Isn't all that you ask for to replace the words "category theory" with "the notion of category" throughout the document?
