Episode Details

Joe Armstrong once said anyone can write a type system covering 90% of Erlang — it's the remaining 10% that defeats even the brightest minds in computer science. He was referring to Philip Wadler. That was 1995. Thirty years later, the BEAM is finally converging on an answer.

In this episode, Alan Wyma and Francesco Cesarini sit down with Annette Bieniusa, professor of software technology at RPTU Germany, and Guillaume Dubois, PhD from IRIF Paris now at Dashbit, to dig into what it actually takes to bring static types to Erlang and Elixir — and why it took this long.

Topics include:

• why every serious attempt at typing Erlang since 1995 — soft types, subtyping, Dialyzer — ran into the same wall, and what's genuinely different now

• what set-theoretic types are and why they're the foundation Elixir 1.2's type system is built on

• how Elixir's gradual type system differs fundamentally from TypeScript or Python's approach — and why baking dynamic in from the start changes everything

• why the BEAM ran telecoms for 25 years without static types, and what problems types are now actually solving

• the risk nobody talks about: developers getting lulled into false confidence by type checking, writing fewer supervision trees and less defensive code

• how Annette's parallel etalizer for Erlang and Guillaume's Elixir work share the same theoretical foundation but make different design choices

• why "type systems don't mean error-free" — and what types actually buy you on the BEAM specifically

• what Elixir 1.2 ships, what's still being worked on, and the one thing you can do this week

Recorded May 28, 2026.