I feel like ... SML is the better language but OCaml is the better runtime/community. Sad.
Back when I was more into looking at this kind of thing (uh, 20 years ago?) I wrote a few simple programs in SML/NJ and far preferred its syntax to OCaml. But even back then, OCaml had more dev community momentum. (Actually Haskell seemed to have even more momentum but I never ever found it readable or comprehensible as a mere mortal.)
At the time for what I was doing, I really wanted... SML but without a garbage collector, operating for systems level programming. And so I was excited when Graydon Hoare started what became Rust. Which is what I prefer to work in these days.
Still, if I wanted a language for higher level development, I really would prefer to reach for something in the ML family of languages, they are just very expressive. But I wouldn't do this for paid employment work, too esoteric. Maybe that will change a bit now that Rust has brought some concepts and syntax from ML to the mainstream.
Can anyone say which implementation specifically?
Strangely I think SML focus on being well defined and tidy is why it never really took off. A language success is linked to its community and your features define who will want to join you. It seems to me that at the beginning it’s better to attract tinkerers than perfectionists.
That statement needs some evidence.
> a lot more functionalities
Past a certain minimal threshold of needed functionality, I prefer a language not to have a couple good features than to have a really bad one, like implementation inheritance, particularly multiple inheritance.
SML has multiple, mostly independent implementations with different characteristics. Poly/ML had multi-processor support well before OCaml. But OCaml development is certainly much more active.