Objects, Interference, and the Yoneda Embedding

Abstract

We present a new semantics for Algol-like languages that combines methods from two prior lines of development: •the object-based approach of [21,22], where the meaning of an imperative program is described in terms of sequences of observable actions, and•the functor-category approach initiated by Reynolds [24], where the varying nature of the run-time stack is explained using functors from a category of store shapes to a category of cpos.The semantics gives an account of both the phemomena of local state and irreversibility of state change. As an indication of the accuracy obtained, we present a full abstraction result for closed terms of second-order type in a language containing active expressions, i.e. value-returning commands.