Effpi: verified message-passing programs in Dotty

We present Effpi: an experimental toolkit for strongly-typed concurrent and distributed programming in Dotty, with verification capabilities based on type-level model checking. Effpi addresses a main challenge in creating and maintaining concurrent programs: errors like protocol violations, deadlocks, and livelocks are often spotted late, at run-time, when applications are tested or (worse) deployed. Effpi aims at finding them early, when code is written and compiled. Effpi provides: (1) a set of Dotty classes for describing communication protocols as types; (2) an embedded DSL for concurrent programming, with process-based and actor-based abstractions; (3) a Dotty compiler plugin to verify whether protocols and programs enjoy desirable properties, such as deadlock-freedom; and (4) an efficient run-time system for executing Effpi's DSL-based programs. The combination of (1) and (2) allows the Dotty compiler to check whether an Effpi program implements a desired protocol/-type; and this, together with (3), means that many typical concurrent programming errors are found and ruled out at compile-time. Further, (4) allows to run highly concurrent Effpi programs with millions of interacting processes/actors, by scheduling them on a limited number of CPU cores. In this paper, we give an overview of Effpi, illustrate its design and main features, and discuss its future.