Rast: A Language for Resource-Aware Session Types

Abstract

Traditional session types prescribe bidirectional communication protocols forconcurrent computations, where well-typed programs are guaranteed to adhere tothe protocols. However, simple session types cannot capture properties beyondthe basic type of the exchanged messages. In response, recent work has extendedsession types with refinements from linear arithmetic, capturing intrinsicattributes of processes and data. These refinements then play a central role indescribing sequential and parallel complexity bounds on session-typed programs.The Rast language provides an open-source implementation of session-typedconcurrent programs extended with arithmetic refinements as well as ergometricand temporal types to capture work and span of program execution. To furthersupport generic programming, Rast also enhances arithmetically refined sessiontypes with recently developed nested parametric polymorphism. Type checkingrelies on Cooper's algorithm for quantifier elimination in Presburgerarithmetic with a few significant optimizations, and a heuristic extension tononlinear constraints. Rast furthermore includes a reconstruction engine sothat most program constructs pertaining the layers of refinements and resourcesare inserted automatically. We provide a variety of examples to demonstrate theexpressivity of the language