By integrating constructs from the λ-calculus and the π-calculus, in higher-order process calculi exchanged values may contain processes. This paper studies the relative expressiveness of HOπ, the higher-order π-calculus in which communications are governed by session types. Our main discovery is that HO, a subcalculus of HOπ which lacks name-passing and recursion, can serve as a new core calculus for session-typed higher-order concurrency. We show that HO can encode HOπ fully abstractly (up to typed contextual equivalence) more precisely and efficiently than the first-order session π-calculus (π). Overall, under the discipline of session types, HOπ, HO, and π are equally expressive; however, we show that HOπ is more tightly related to HO than to π.

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Information and Computation

Kouzapas, D., Pérez Parra, J., & Yoshida, N. (2019). On the relative expressiveness of higher-order session processes. Information and Computation, 268, 104433:1–104433:54. doi:10.1016/j.ic.2019.06.002