Runners in Action

Abstract

Runners of algebraic effects, also known as comodels, provide a mathematical model of resource management. We show that they also give rise to a programming concept that models top-level external resources, as well as allows programmers to modularly define their own intermediate “virtual machines”. We capture the core ideas of programming with runners in an equational calculus, which we equip with a sound and coherent denotational semantics that guarantees the linear use of resources and execution of finalisation code. We accompany with examples of runners in action, provide a prototype language implementation in OCaml, as well as a Haskell library based on.