StandardML is a rather nice modular high level functional programming language with algebraic datatypes, pattern matching, compile-time type checking and type inference etc. Poly/ML extends this with strong proven multi-core and cross platform support including Posix threads, parallel garbage collection, FFI etc. Poly/ML has been around a while, but it is still actively maintained by Dave Mathews et al (most recent release June 2026) has good windows and X11 support. Poly/ML is a great way to explore the world of StandardML and is used to build Isabelle and HOL theorem provers. Definitely worth a look!

I had just never heard of it before, I didn't realize it was well know. I was quoting from it's specification.