I do mostly use a strictly FP language, but it's trivial to use Java (C#, etc) as FP languages too. Just use classes as stateless function namespaces. FP Java is best Java.
> And all the stuff like factories and everything exist in FP as well, it's pretty short sighted to say otherwise. These are patterns that may or may not be useful in a given case. Sometimes a language feature can replace them (e.g. pattern matching ~ visitor pattern, but not even this is a full match see closed vs open hierarchy), but in most cases you just call them something else/don't have that problem because you are not writing that big of a software.
This is precisely the viewpoint that made me want to reply to the original comment. If you live and breathe OOP, you see OOP design patterns as solutions, because you've run into OOP problems that they solve. FP code does not tend to run into OOP problems, and ergo does not tend to utilise OOP solutions to those problems. I appreciate this can be hard to imagine, but I respectfully suggest you have some OOP blinders on if you're so confident everyone is using factories that you attempt to size-shame FP codebases you've not even seen so you can remain in the right. :)
The purpose of factories is to decouple object creation and use. But FP already does this by never coupling behaviour and data in the first place. Think about it. If data is in a simple struct, with no member functions, ideally immutable, what kind of factory could you possibly need? How would it even work? What kind of problem could it possibly solve?
To say nothing of e.g. the Visitor pattern, which is an approximation of functional styles using OOP. There is no need to define some small subset of behaviour outside a class, and then hook up boilerplate machinery inside that class to run that behaviour (ie the Visitor pattern) if all behaviour is always defined outside the class. The Visitor pattern solves a problem that arises only in OOP, due to its penchant for stateful data-code coupling, and it does so with a sprinkling of FP. It's incoherent to speak of a Visitor pattern in FP code. It's an OOP solution to an OOP problem.