&gt; Nowhere is the categorical view more visible than in Haskell<p>and the author&#x27;s point when he writes <i>In ... Haskell ... types ... are built in, rather than being defined by universal constructions</i> [+]  is indeed that current programming languages don&#x27;t entirely capture what category theory is about in practice.<p>[+] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Universal_property" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Universal_property</a>