I dare to disagree - I still think that functional programming is a FAD of the day right now. Like object oriented was the FAD of the day in the 1990s and many then procedural languages saw OOP extensions on top of them (Perl where you need a bless() to work with an object? :-D ) and some even were like "yeah everything is an object so let's wrap every procedure into a class and use Command Pattern instead of closures and build a Kingdom of Nouns where people will name their classes after design patterns and everything will be perfect with a cup of hot Java").

Nowadays C++ has closures. What will become the FAD of the day in 10 years? Will wee see embedded Prolog in C# 12 or C++31? Who knows? Like OOP has been with us since 1968? and hasn't disappeared anywhere, functional programming features will not disappear from mainstream languages. But the "cool new shiny silver bullet" will be something else. Like Simula-68 and Smalltalk-80 paved way for OOP, Haskell and OCaml (et. al.) have been paving way for functional programming and Prolog and Datalog have been paving way for logical programming. They won't become mainstream when logical programming becomes the FAD of the day.

BTW you mentioned you taught a couple of junior programmers an ML-ish language. That's awesome! We all (programming community) need more legends like you.

> Ocaml's standard library is a huge sore point.

I think this is a bit overstated. It's roughly the same size of JavaScript, missing regexes but having some stuff that JS lacks. And in lots of languages with large standard libraries, people tend to use standard library replacements. Considering that htere are also not a lot of people working on OCaml, the core team time is better spent on stuff like multicore rather than HTTP servers and clients.

The standard library is also open to contributions. For example, in OCaml 4.14, 44 functions were added in the module Seq https://v2.ocaml.org/api/Seq.html. String also had a lot of utility functions for integer decoding in 4.13 https://v2.ocaml.org/api/String.html.

Nit : From what I remember and most unintuitively Reason is the language/alternative Ocaml syntax and ReasonML is its umbrella project.

The alternative Base/Core from Jane Streets looks good though. Of course it splits the community but the work done on it is very good.

I think its because influential companies in the tech space pushed them. For instance, Go is backed by Google, and they made alot of rounds evangelizing Go.

Kotlin is a Jetbrains project and it certainly didn't hurt that Google made Kotlin the preferred language over Java for development on Android, and that Kotlin itself has great Java ecosystem compatibility.

For years, Rust was Mozilla's baby, and they did a lot of good work evangelizing Rust for its use case, and other companies adopted it as well, continuing the cycle.

There is nothing I can think of that is comparable for F#, OCaml, Haskell and many other fine languages

I'm pretty confident we will find a fairly direct correlation between how mainstream the language has become and how much money was poured into its development (i.e. headcount of engineers working on the project and their salary levels).

Now I know correlation does not equal causation. But you have to think it must have some effect when Google is paying its Distinguished Engineers--the likes of Rob Pike, Ken Thompson--plus at least several more engineers, project managers, and others. All to work on Go. Can you imagine what the OCaml ecosystem could do with that kind of money and dedicated engineering talent? Heck, any technology for that matter.