Stephanie Balzer (Carnegie Mellon University, USA) gives the third talk in the third panel, Contracts and Sessions, on the 3rd day of the ICFP conference. Co-written Frank Pfenning (Carnegie Mellon University, USA).

Session-typed languages building on the Curry-Howard isomorphism between linear logic and session-typed communication guarantee session fidelity and deadlock freedom. Unfortunately, these strong guarantees exclude many naturally occurring programming patterns pertaining to shared resources. In this paper, we introduce sharing into a session-typed language where types are stratified into linear and shared layers with modal operators connecting the layers. The resulting language retains session fidelity but not the absence of deadlocks, which can arise from contention for shared processes. We illustrate our language on various examples, such as the dining philosophers problem, and provide a translation of the untyped asynchronous pi-calculus into our language. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/