Comment by gf000

I am fairly familiar with FP concepts, though lack experience with large FP-only code bases, so I don't think the OOP-blinder things apply to me.

Visitor pattern is meant to address the other half of the expression problem - you have n types of data all with m behaviors. OOP makes it easy to add a new row (new class) while FP makes it easy to add a new column (new function). But both are asymmetrical, traits a la rust are probably the closest to solving it properly. So no, it is incorrect assumption on your part to hand wave it away, this is not solved (especially not in "FP java", which otherwise I also like and use).