[phlakaton]

You can name almost anything (these are general-purpose languages, after all), but I'll just throw a couple of things out there:

1. A compiler. The actual algorithms and datastructures might not be all that interesting (or they might be if you're really interested in that sort of thing), but the kinds of transformations you're doing from stage to stage are sophisticated.

2. An analytics pipeline. If you're working in the Spark/Scala world, you're writing high-level functional code that represents the transformation of data from input to output, and the framework is compiling it into a distributed program that loads your data across a cluster of nodes, executes the necessary transformations, and assembles the results. In this case there is a ton of stateful I/O involved, all interleaved with your code, but the framework abstracts it away from you.

[whatnow37373]

Thanks, especially two is very interesting. Admittedly the framework itself is the actually interesting part and that's what I meant with this work being "rare" (I mean how many people work on those kinds of frameworks fulltime? It's not zero, but..)

I think what I engaged with is the notion that most programming "has some side-effects" ("it's not 100% pure"), but much of what I see is like 95% side-effects with some cool, interesting bits stuffed in between the endless layers of communication (without which the "interesting" stuff won't be worth shit).

I feel FP is very, very cool if you got yourself isolated in one of those interesting layers but I feel that's a rare place to be.

[phlakaton]

Yeah, it's not that e.g. Haskell won't allow side effects, it's that side effects are constrained: 1) all the side-effectful operations have types that forbid you from using them outside of a side-effect context; 2) and it's a good thing they do, because Haskell's laziness means the results you would get otherwise are counterintuitive.

Other FP frameworks are far less strict about such things, and many FP features are now firmly in the mainstream. So no, I don't think this stuff is particularly rare, though Haskell/OCaml systems probably still are. There are pluses and minuses with structuring code in a pure-core-with-side-effect-shell way – FP enthusiasts tend to think the pluses outweigh the minuses.

Best, I think, to view FP not as dogma or as a class of FP-only languages, but rather as a paradigm first, a set of languages second.