I have the compiler on GitHub [1] - I just started working on it again after a 2-year hiatus (to finish my PhD).

As for language-server, I'm currently sketching out some plans to use SMLnj's "Visible Compiler" feature, since that seems the easiest path forward. I have a half-baked language-server based on MLton's def-use output, but it's too unstable to share. I am planning to make some progress on the language-server in the next couple weeks.

[1] You'll notice it's just a fragment of the language for now, and only half-implemented. https://github.com/SomewhatML/sml-compiler and https://github.com/SomewhatML/sml-analyzer (again for a fragment of SML)