[bunderbunder]

ML (short for "meta-language") was originally designed for use in programming language research, and really shines for that purpose. And OCaml is probably the most pragmatic dialect for the purpose.

SML is very dated and the standard library and ecosystem lack many things that are considered table stakes for a viable programming language nowadays. And F# and Scala are fine as enterprise languages, but being tied to .NET and Java respectively makes them less desirable for implementing a language that won't itself be coupled to one of those runtimes.