Simple Refinement of Anonymous Sum Types in Pattern Matches

https://ayazhafiz.com/articles/22/simple-flow-refinement-of-anonymous-sum-types · I describe a simple, "zero-cost" system for adding flow-typing-like refinement of anonymous sum types to a language, with a model of compilation that supports unboxed, non-uniform representations. The system extends naturally to also support type expansion (the opposite of refinement) thanks to its reliance on unification.