Classical BI: Its Semantics and Proof Theory

We present Classical BI (CBI), a new addition to the family of bunched logics which originates in O'Hearn and Pym's logic of bunched implications BI. CBI differs from existing bunched logics in that its multiplicative connectives behave classically rather than intuitionistically (including in particular a multiplicative version of classical negation). At the semantic level, CBI-formulas have the normal bunched logic reading as declarative statements about resources, but its resource models necessarily feature more structure than those for other bunched logics; principally, they satisfy the requirement that every resource has a unique dual. At the proof-theoretic level, a very natural formalism for CBI is provided by a display calculus \`a la Belnap, which can be seen as a generalisation of the bunched sequent calculus for BI. In this paper we formulate the aforementioned model theory and proof theory for CBI, and prove some fundamental results about the logic, most notably completeness of the proof theory with respect to the semantics.Comment: 42 pages, 8 figure

A Pragmatic Type System for Deductive Verification

In the context of deductive verication, it is customary today to handle programs with pointers using either separation logic, dynamic frames, or explicit memory models. Yet we can observe that in numerous programs, a large amount of code ts within the scope of Hoare logic, provided we can statically control aliasing. When this is the case, the code correctness can be reduced to simpler verication conditions which do not require any explicit memory model. This makes verication conditions more amenable both to automated theorem proving and to manual inspection and debugging. In this paper, we devise a method of such static aliasing control for a programming language featuring nested data structures with mutable components. Our solution is based on a type system with singleton regions and eects, which we prove to be sound

A bunch of sessions:a propositions-as-sessions interpretation of bunched implications in channel-based concurrency

The emergence of propositions-as-sessions, a Curry-Howard correspondence between propositions of Linear Logic and session types for concurrent processes, has settled the logical foundations of message-passing concurrency. Central to this approach is the resource consumption paradigm heralded by Linear Logic. In this paper, we investigate a new point in the design space of session type systems for message-passing concurrent programs. We identify O’Hearn and Pym’s Logic of Bunched Implications (BI) as a fruitful basis for an interpretation of the logic as a concurrent programming language. This leads to a treatment of non-linear resources that is radically different from existing approaches based on Linear Logic. We introduce a new π-calculus with sessions, called πBI; its most salient feature is a construct called spawn, which expresses new forms of sharing that are induced by structural principles in BI. We illustrate the expressiveness of πBI and lay out its fundamental theory: type preservation, deadlock-freedom, and weak normalization results for well-typed processes; an operationally sound and complete typed encoding of an affine λ-calculus; and a non-interference result for access of resources

Strong update, disposal and encapsulation in bunched typing

We present a bunched intermediate language for strong (type-changing) update and disposal of first-order references. In contrast to other substructural type systems, the additive constructs of bunched types allow the encapsulation of state that is shared by a collection of procedures. Key words: bunched typing, separation logic, strong update, disposal, encapsulation, continuation-passing style