That's not really true. When some people claim you must learn category theory to use Haskell, they mean they have to learn the math-subject-capital-letter Category Theory, which goes way beyond programming and comes with a lot of baggage.
They never mean you have to learn Functor, Applicative, etc as used in Haskell and taught in every tutorial. If they did mean the latter, it would be a tautology, which is not very useful.
Compare "in order to do OOP you have to learn what an object truly is, its essence, and possibly take some courses on the philosophy of being" vs "you have to learn about methods and objects".
> It's like saying "you can learn how to do unions, intersections, and differences on collections of unique objects without understanding set theory".
You can totally do unions, intersections and differences without knowing set theory.
They never mean you have to learn Functor, Applicative, etc as used in Haskell and taught in every tutorial. If they did mean the latter, it would be a tautology, which is not very useful.
Compare "in order to do OOP you have to learn what an object truly is, its essence, and possibly take some courses on the philosophy of being" vs "you have to learn about methods and objects".
> It's like saying "you can learn how to do unions, intersections, and differences on collections of unique objects without understanding set theory".
You can totally do unions, intersections and differences without knowing set theory.