https://elixir-lang.org/blog/2026/01/09/type-inference-of-all-and-next-15/

For about five years Elixir contributors have been working on integrating a type system into the language and tooling. Starting with the development of a pretty novel and unorthodox type system.

I'm fascinated by several things:

— they still haven't dropped the project. Despite slow progress and obstacles in performance and usability they systematically overcome.

— they are deeply committed to the soundness of their gradual type system, which is tricky (and to my eyes they sometimes confuse soundness and completeness in the blogs at least)

— they put end-user (developer) usability front and center, in terms of speed and responsiveness, type inference to reduce annotation burden, meaningful error messages, etc.

Towards that goals the post references their work on
https://elixir-lang.org/blog/2023/09/20/strong-arrows-gradual-typing/
and the development of
https://elixir-lang.org/blog/2025/12/02/lazier-bdds-for-set-theoretic-types/
which are cool in their own right.