Speak Now: Safe Actor Programming with Multiparty Session Types

2026-02-27

AI Summary

This work addresses the lack of formal communication protocols in actor models, which often leads to protocol mismatches and deadlocks. To resolve this, the authors propose Maty, a novel language that integrates multiparty session types (MPST) statically into an actor system supporting multiple concurrent sessions. Maty preserves key actor model properties—such as scalability, fault tolerance, and Erlang-style supervision—while ensuring communication safety through a flow-sensitive effect system, an event-driven programming style, and first-class message handlers. Empirical evaluation demonstrates that Maty can express complex systems efficiently, including the Savina benchmark suite, industrial-scale factory automation scenarios, and a chat server, thereby offering both expressive power and strong formal guarantees for communication correctness.

Technology Category

• Multiagent Systems: Agent Communication
• Planning, Routing, and Scheduling: Model-Based Reasoning
• Natural Language Processing: Safety and Robustness

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• Semantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactions

Abstract

Actor languages such as Erlang and Elixir are widely used for implementing scalable and reliable distributed applications, but the informally-specified nature of actor communication patterns leaves systems vulnerable to costly errors such as communication mismatches and deadlocks. Multiparty session types (MPSTs) rule out communication errors early in the development process, but until now, the many-sender, single-receiver nature of actor communication has made it difficult for actor languages to benefit from session types. This paper introduces Maty, the first actor language design supporting both static multiparty session typing and the full power of actors taking part in multiple sessions. Maty therefore combines the error prevention mechanism of session types with the scalability and fault tolerance of actor languages. Our main insight is to enforce session typing through a flow-sensitive effect system, combined with an event-driven programming style and first-class message handlers. Using MPSTs allows us to guarantee communication safety: a process will never send or receive an unexpected message, nor will a session get stuck because an actor is waiting for a message that will never be sent. We extend Maty to support Erlang-style supervision and cascading failure, and show that this preserves Maty's strong metatheory. We implement Maty in Scala using an API generation approach, and demonstrate the expressiveness of our model by implementing a representative sample of the widely-used Savina actor benchmark suite; an industry-supplied factory scenario; and a chat server.

Problem

• actor programming
• multiparty session types
• communication safety
• deadlock
• type system

Innovation

• Multiparty Session Types
• Actor Model
• Flow-sensitive Effect System
• Communication Safety
• Static Typing