Fundamentals of Elixir's Upcoming Type System

José Valim's keynote explores the rationale and framework for introducing gradual static typing into Elixir through a system based on set theoretic types, which utilizes unions, intersections, and negations. The new type system aims to provide better code maintenance, improve documentation, enhance developer experience, and serve as a design tool while ensuring no performance compromise. Saturated types offer expressiveness to capture Elixir idioms with precision and a simple reasoning foundation, yet require explicit type annotations. The gradual typing approach facilitates interaction between static and dynamic code, promoting easier adoption without rewriting existing code. Strong arrows and type inference from patterns and guards are innovations that tame the dynamic type's spread in the codebase, maintaining runtime consistency without performance costs. This approach is unique to Elixir, and its development is ongoing, with more research yet to be explored. Valim emphasizes the non-disruptive nature of introducing this type system and aims for community-wide patience and cooperation during the transition. The roadmap's initial goal is to add set theoretic types to the compiler with inferred types from existing code patterns and guards, followed by adding type specificity to structs and, eventually, the whole function typing.