[EdSharkey]

Imperative shell, (ever-expanding-through-relentless-refactoring) functional core seems to work pretty well for practical applications. Modern Java gets the job done in that regard.

What I don't like is the concentration level required for functional productions over equivalent imperative routines. I have found it difficult to impress upon junior developers the testing advantages of functional programming and in refactoring pairing sessions with them, they quickly lose the thread and go all doe eyed.

I feel like the current functional programming paradigms favor terseness that completely obliterates the thought process that led to the production. So, even if junior has the aha moment when we reach the end of the production, and understands what we just achieved there in 6 lines of dense code, they'd be at a loss to retrace it themselves in the future because the thought processes of each operator in the production require too much simulation space in the head.

That, and libraries like RxJS that layer in concepts of time and observables and higher-order observables with sneaky completion states that only stretch the mind further because the true semantics of the program are coupled with under-documented quirky edge cases of the operators. Running into one of those while pairing with junior is not exactly confidence building.

Long-form programming with named pure functions might help, but then I suppose you can lose the terseness and can get lost in a sea of 1-line named functions.