> Want to write ML, probably best to use a language with functions as first class types (ie a FP language). You might say, most people doing ML use Python. This came to be because the language was picked based upon what people knew. But the big companies doing ML (successfully) don't use Python anymore and haven't for over a decade. ML researchers kept FP alive for several decades when nobody else cared because FP is the best tool for ML (or for writing a compiler).

I strongly disagree. The top AI companies are using a lot of Python (although sure they also use other languages too, but they're definitely using Python!). Even if by ML you mean old-school ML techniques, a ton of big companies also use Python for this (some might use MATLAB or R).

On the other hand I don't know of a single large company using an FP language for ML, unless you count something like Spark (which I would push back on: the Scala API of Spark is not really FP and almost all users of Spark that I know of program mainly in the more OO part of Scala rather than its FP part).

Even die-hard FP companies such as Jane Street use Python for their ML (see e.g. https://www.janestreet.com/join-jane-street/position/4276720... which notably mentions Python and does not mention OCaml).

Do you know of any company with a team of over 50 ML researchers (either old-school ML or modern AI) using an FP language as their primary workhorse for that team? Because I can't think of a single one.

More to the point, do you know of any ML researcher (and who is acknowledged as primarily an ML researcher by other ML researchers) who primarily programs in an FP language?

Even in the golden era of symbolic AI from the 70s and 80s they still weren't using FP languages (they basically didn't exist yet). The closest you could say is that they were using Lisps, but Lisps aren't FP languages by default. Some are (e.g. Clojure), but many aren't or at least aren't any more FP than any other multiparadigmatic language (e.g. Common Lisp). And again I don't know of any significant ML work being done in Lisps at this point (there's some scattered small teams and individuals doing work there, but nothing that I think could rise to the level of "big ML company").