You might peek at Coalton. https://coalton-lang.github.io/reference/ https://coalton-lang.github.io/reference/ I don’t think it has sum types, but it offers a

You might peek at Coalton. https://coalton-lang.github.io/reference/ https://coalton-lang.github.io/reference/ I don’t think it has sum types, but it offers a rather sophisticated and very functionally oriented type system that compiles back to SBCL. It looks neat, haven’t found time to play yet…