Game semantic analysis of equivalence in IMJ

Using game semantics, we investigate the problem of verifying contextual equivalences in Interface Middleweight Java (IMJ), an imperative object calculus in which program phrases are typed using interfaces. Working in the setting where data types are non-recursive and restricted to finite domains, we identify the frontier between decidability and undecidability by reference to the structure of interfaces present in typing judgments. In particular, we show how to determine the decidability status of problem instances (over a fixed type signature) by examining the position of methods inside the term type and the types of its free identifiers. Our results build upon the recent fully abstract game semantics of IMJ. Decidability is proved by translation into visibly pushdown register automata over infinite alphabets with fresh-input recognition

Unbounded Allocation in Bounded Heaps

International audienceIn this paper we introduce a new symbolic semantics for a class of recursive programs which feature dynamic creation and unbounded allocation of objects. We use a symbolic representation of the program state in terms of equations to model the semantics of a program as a pushdown system with a finite set of control states and a finite stack alphabet. Our main technical result is a rigorous proof of the equivalence between the concrete and the symbolic semantics.Adding pointer fields gives rise to a Turing complete language. However, assuming the number of reachable objects in the visible heap is bounded in all the computations of a program with pointers, we show how to construct a program without pointers that simulates it. Consequently, in the context of bounded visible heaps, programs with pointers are no more expressive than programs without them