Typing and Subtyping Mobility in Boxed Ambients

We provide a novel type system for Bugliesi et al.’s Boxed Ambients that combines value subtyping with mobility types. The former is based on read/write exchange types, the latter builds on the notion of ambient group. Mobility types allow to specify where an ambient is allowed to stay, closing existing expressiveness gaps in the literature at no additional complexity costs. Subtyping is aimed at achieving maximal generality on both communication and mobility types. We then introduce co-capabilities to express explicit permissions to access ambients. In this setting, ambient types are refined to specify who is allowed to enter an ambient, making a promising framework to model open systems.