Partially typed multiparty sessions with internal delegation

Abstract

A multiparty session formalises a set of concurrent communicating participants. The possibility for a participant to delegate some interactions to another participant is crucial for the expressivity of multiparty sessions. We propose the first type system for multiparty sessions with delegation where some communications between participants can be ignored. This allows us to type some sessions with global types representing interesting protocols, which have no type in the standard type systems. Our type system enjoys Subject Reduction, Session Fidelity and partial Lock-freedom. The last property ensures the absence of locks for participants with non-ignored communications. A sound and complete type inference algorithm is also discussed.