Quantitative Types in Idris 2

An introduction to how Idris 2 uses Quantitative Type Theory to support linear and dependent types.

Dependent types allow us to express precisely what a function is intended to do. Recent work on Quantitative Type Theory (QTT) extends dependent type systems with linearity, also allowing precision in expressing when a function can run. This is promising, because it suggests the ability to design and reason about resource usage protocols, such as we might find in distributed and concurrent programming, where the state of a communication channel changes throughout program execution. Up to now, however, there has not been a full-scale programming language with which to experiment with these ideas. Idris 2 is a new version of the dependently typed language Idris, with a new core language based on QTT, supporting linear and dependent types. In this talk I will show the benfits of QTT in Idris 2, in particular how it improves interactive program development by reducing the search space for type-driven program synthesis; and, how resource tracking in the type system leads to type-safe concurrent programming with session types. Presented by Edwin Brady