[daxfohl]

Depends on what you're doing. Scott Wlaschin did the best modern take on that here: https://fsharpforfunandprofit.com/posts/13-ways-of-looking-a.... It shows incrementally going from a purely (haha) procedural implementation all the way up to brain-exploding free monads, all doing essentially the same thing: a basic implementation of the old turtle game.

My take is you should know all these, and choose the appropriate level for what you're doing. You don't need to crank it up to 13 everywhere just because it's there. I spend most of my time (web apis, business logic) around level 7. If you dial the abstraction level too far up, not only does the code seem confusing, but it's also easy to paint yourself into an abstraction corner, where a new requirement comes in that breaks the abstraction, so you end up either tearing it down and rebuilding it completely, or building up a terrible "spaghetti abstraction" which is the worst kind of spaghetti. It's a bit ironic to think that abstractions are exactly what's supposed to prevent you from being painted into a corner, but it can happen easily. (https://www.sandimetz.com/blog/2016/1/20/the-wrong-abstracti... is a good reference).

When writing things like compilers, the abstraction level can comfortably go higher. In fact it should. It makes challenging logic far easier to reason about and more consistent to specify and implement when you can think about it mathematically. Other things like rules engines and such can live comfortably in between the two. Conversely when writing timing-critical device code then the appropriate level of abstraction is much lower. A good reference for this style is the k8s PV code. Note the comments starting on line 55 (tldr: DO NOT SIMPLIFY THIS CODE) https://github.com/kubernetes/kubernetes/blob/ec2e767e593953...

So as developers we have to determine what the appropriate level of abstraction should be for our use cases. In fact I'd offer that's one of the most important parts of software design. But it's important to know all of them so we can choose accordingly.