I'm talking about the difficultly of reasoning about high level application state when it isn't explicit. To take a low level example - sorting a list efficien

I'm talking about the difficultly of reasoning about high level application state when it isn't explicit. To take a low level example - sorting a list efficiently is easy with imperative programming and mutable state ( Note you can still encapsulate that state within a object - it doesn't need to be global ). On the other hand took about 20 years before somebody worked how to do it reasonably with a functional approach. Being obsessive about a pure functional approach and/or having a holy war against heap managed state is a mistake in my view. Functional approach is a tool in the toolbox, not a golden hammer.