A Calculus for Concurrent Objects

This paper presents an imperative and concurrent extension of the functional objectoriented calculus described in [FHM94]. It belongs to the family of so-called prototypebased object-oriented languages, in which objects are created from existing ones via the inheritance primitives of object extension and method override. Concurrency is introduced through the identi cation of objects and processes. To our knowledge, the resulting calculus is the rst concurrent object calculus to be studied. We de ne an operational semantics for the calculus via a transition relation between con gurations, which represent snapshots of the run-time system. Our static analysis includes a type inference system, which statically detects message-not-understood errors, and an e ect system, which guarantees that synchronization code, speci ed via guards, is side-e ect free. We present a subject reduction theorem, modi ed to account for imperative and concurrent features, and type and e ect soundness theorems.