π-calculus, Session Types research at the University of Oxford
Session types provide a flexible programming style for structuring interaction, and are used to guarantee a safe and consistent composition of distributed processes. Traditional session types include only one-directional input (external) and output (internal) guarded choices. This prevents the session-processes to explore the full expressive power of the π-calculus where the mixed choices are proved more expressive than the (non-mixed) guarded choices. To account this issue, recently Casal, Mordido, and Vasconcelos proposed the binary session types with mixed choices (CMV+). This paper carries a surprising, unfortunate result on CMV+: in spite of an inclusion of unrestricted channels with mixed choice, CMV+’s mixed choice is rather separate and not mixed. We prove this negative result using two methodologies (using either the leader election problem or a synchronisation pattern as distinguishing feature), showing that there exists no good encoding from the π-calculus into CMV+, preserving distribution. We then close their open problem on the encoding from CMV+ into CMV (without mixed choice), proving its soundness and thereby that the encoding is good up to coupled similarity.
@inproceedings{PY2022,
author = {Kirstin Peters and Nobuko Yoshida},
title = {{On the Expressiveness of Mixed Choice Sessions}},
booktitle = {Expressiveness in Concurrency and Structural Operational Semantics 2022},
volume = {368},
pages = {113--130},
publisher = {Open Publishing Association},
year = 2022
}
@inproceedings{PY2022,
author = {Kirstin Peters and Nobuko Yoshida},
title = {{On the Expressiveness of Mixed Choice Sessions}},
booktitle = {Expressiveness in Concurrency and Structural Operational Semantics 2022},
volume = {368},
pages = {113--130},
publisher = {Open Publishing Association},
doi = "10.4204/eptcs.368.7",
year = 2022
}