> I wouldn't say there is any threshold where purely functional programming shines less. But what is the set of problems you are usually solving? Any problem s

> I wouldn't say there is any threshold where purely functional programming shines less. But what is the set of problems you are usually solving? Any problem set that involves a lot of mutable set is not well-suited for functional programming, in my opinion. And maybe problems where efficiency is important, although I don't know enough to have an opinion on that. Some areas that come to mind are: - systems programming (which you said) - GUI programming - games - large simulations? Maybe if you can reuse the before and after buffers FP would work okay there. GUI's have a surprising amount of state, which is why immediate-mode GUIs haven't really taken off. (Yes, there's Dear ImGUI, but it actually uses the name of the control to store retained-mode state under the hood) It sounds really good when you think about buttons and sliders, but then you come to text editing or list-box selection...