In our fourth episode, we speak with Stephanie Weirich from the University of Pennsylvania on the Zombie language and Dependent Haskell. Stephanie is a long-time contributor to Haskell, having been involved in the design and implementation of features such as generalized algebraic datatypes, higher-rank polymorphism, type families, and promoted datatypes. She has also been a participant in Trellys, a project with the goal of combining proofs and programming in the same language.

Zombie is a different kind of dependently typed language, eschewing automatic β-reduction in the type checker for an approach based on explicit equality rewriting, which enables new ways of combining proofs and programs, as well as new forms of proof automation. Meanwhile, as languages designed for dependently typed programming come closer to practical applicability, Haskell is also moving towards full dependent types. We discuss the challenges and opportunities available at the cutting edge of Haskell.