A Semantic Deconstruction of Session Types

Doctoral Thesis A Semantic Deconstruction of Session Types by Alceste Scalas This work investigates the semantic foundations of binary session types, by revisiting them in the abstract setting of labelled transition systems. The main insights and contributions are: • a semantically unified approach to the study of session types and CCS processes with synchronous and asynchronous semantics — the latter obtained with the addition of unbounded buffers; • a semantic approach to safety, based on a syntax-independent characterisation of deadlock states, orphan messages and unspecified reception configurations; • an I/O compliance relation between generic behaviours, that we demostrate to be sound and complete w.r.t. safety in asynchronous session types; • an I/O simulation relation between generic behaviours, which generalises the usual syntax-directed notions of typing and subtyping, encompassing synchronous and asynchronous session types; • a proof-of-concept syntax-driven type system developed from the semantic setting through a (partial) axiomatisation of I/O simulation. This work extends the session types theory to some common programming patterns which are not typically addressed in the session types literature, and aims at setting the ground for further improvements.