I did Advent of Code in SML a couple years ago. It was an interesting experience. I don't think I've ever previously experienced such a vast disconnect between the quality of the core language, and the lack of functionality in the standard library.
I think that it could have easily been my favorite dialect of ML if its standard library hadn't been so anemic even by 1990s standards. As it is, though, my AoC solutions tended to take a large effort, not because the problems were difficult to solve in the language, but because I ended up having to build up so many of my own algorithms and data structures. Fortunately, doing that in in SML is a genuine joy. But it still, sadly, renders the language irrelevant for just about any practical purpose nowadays.
I think that it could have easily been my favorite dialect of ML if its standard library hadn't been so anemic even by 1990s standards. As it is, though, my AoC solutions tended to take a large effort, not because the problems were difficult to solve in the language, but because I ended up having to build up so many of my own algorithms and data structures. Fortunately, doing that in in SML is a genuine joy. But it still, sadly, renders the language irrelevant for just about any practical purpose nowadays.