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Multiparty Session Programming With Global Protocol Combinators

Authors Keigo Imai , Rumyana Neykova , Nobuko Yoshida , Shoji Yuen

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Author Details

Keigo Imai
  • Gifu University, Japan
Rumyana Neykova
  • Brunel University London, United Kingdom
Nobuko Yoshida
  • Imperial College London, United Kingdom
Shoji Yuen
  • Nagoya University, Japan


We thank Jacques Garrigue and Oleg Kiselyov for their comments on an early version of this paper.

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Keigo Imai, Rumyana Neykova, Nobuko Yoshida, and Shoji Yuen. Multiparty Session Programming With Global Protocol Combinators. In 34th European Conference on Object-Oriented Programming (ECOOP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 166, pp. 9:1-9:30, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2020)


Multiparty Session Types (MPST) is a typing discipline for communication protocols. It ensures the absence of communication errors and deadlocks for well-typed communicating processes. The state-of-the-art implementations of the MPST theory rely on (1) runtime linearity checks to ensure correct usage of communication channels and (2) external domain-specific languages for specifying and verifying multiparty protocols. To overcome these limitations, we propose a library for programming with global combinators - a set of functions for writing and verifying multiparty protocols in OCaml. Local behaviours for all processes in a protocol are inferred at once from a global combinator. We formalise global combinators and prove a sound realisability of global combinators - a well-typed global combinator derives a set of local types, by which typed endpoint programs can ensure type and communication safety. Our approach enables fully-static verification and implementation of the whole protocol, from the protocol specification to the process implementations, to happen in the same language. We compare our implementation to untyped and continuation-passing style implementations, and demonstrate its expressiveness by implementing a plethora of protocols. We show our library can interoperate with existing libraries and services, implementing DNS (Domain Name Service) protocol and the OAuth (Open Authentication) protocol.

Subject Classification

ACM Subject Classification
  • Software and its engineering → Concurrent programming structures
  • Theory of computation → Type structures
  • Software and its engineering → Functional languages
  • Software and its engineering → Polymorphism
  • Multiparty Session Types
  • Communication Protocol
  • Concurrent and Distributed Programming
  • OCaml


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