Even experiences FP folks complain about how difficult it is to program in Haskell due to its purity. Further, the high barrier to entry you describe is an even bigger deal to organizations than to individuals. It’s a cost that needs to be paid for every employee. And it’s not just the language features, but FP languages tend to have issues like poor documentation, poor editor integrations, multiple standard libraries, multiple build tools, multiple string types, home-grown project file syntax, multiple preludes, many extensions, etc. All of these boost the learning curve in addition to the issues with the language itself.

In my limited experience with functional programming, I've come away with the impression that the problems you're describing are why you don't see a lot of companies that use FP exclusively.

But I think the advantages that OP is lauding are also there, and "space shuttle code" might just be where it shines. Reading that comment in this post made me immediately think of Haskell. The Clojure components at my company fits the "space shuttle" description of importance, and its dependability is striking compared to the rest of our code. Part of it may be that being written in a different language allows its concerns to be separate from the rest of the application too, but I do think the FP paradigm is simply good in this domain.

Sure, but I doubt all of Kubernetes is written in this style, so it’s probably not worth writing everything in Haskell. Note also that there’s nothing about FP that prohibits it from addressing the aforementioned practical problems. Some Haskell-like could swoop in and totally steal Go’s lunch if they would simply prioritize practicality over experimentation.

> Some Haskell-like could swoop in and totally steal Go’s lunch if they would simply prioritize practicality over experimentation.

I don't know. It seems like it would be easy enough to build an AST to make sure there were no unknown conditions that didn't lead to a return statement.

I don’t understand how your post relates to mine. I was saying that if a static functional language focused more on simplicity, readability, good tooling and documentation, etc then it would eat Go’s lunch without trading off any of Haskell’s important characteristics (I.e., robust type safety).

> I think that's a wrong and outdated view on strong type systems.

I wasn't really talking about type systems specifically, I was thinking along the lines of the Rust borrow checker here, and lower level programming like assembly and C.

> A good type system is also an ergonomic one. What people start to experience is that the compiler is actually a friend that helps you write code and keep yourself true to your own promises.

I see a lot of people make the mistake that type safe code is bug free code. "It compiles, therefore ship it."

> It doesn't come down to trust, it comes down to the realization that your mind can keep track of less information than a computer, and that you, as a programmer, are forgetful and make mistakes. The compiler is there to help you when you stumble over your own feet.

You trust the compiler to find bugs. Awesome. Luck be to you. I trust unit tests more than the compiler. Mostly because I wrote them. The compiler, I didn't.

You don't write the compiler, of course, but you do write or rather design the types that your program uses. The typechecker ensures that they're consistent within the system of logic that they set up.

By your logic, it's not enough to have faith in unit tests because you wrote them; you must also write the test framework and runner.