Linearity, control effects, and behavioral types

Abstract

Mainstream programming idioms intensively rely on state mutation, sharing, and concurrency. Designing type systems for handling and disciplining such idioms is challenging, due to long known conflicts between internal non-determinism, linearity, and control effects such as exceptions. In this paper, we present the first type system that accommodates non-deterministic and abortable behaviors in the setting of sessionbased concurrent programs. Remarkably, our type system builds on a Curry-Howard correspondence with (classical) linear logic conservatively extended with two dual modalities capturing an additive (co)monad, and provides a first example of a Curry-Howard interpretation of a realistic programming language with built-in internal non-determinism. Thanks to its deep logical foundations, our system elegantly addresses several well-known tensions between control, linearity, and non-determinism: globally, it enforces progress and fidelity; locally, it allows the specification of non-deterministic and abortable computations. The expressivity of our system is illustrated by several examples, including a typed encoding of a higher-order functional language with threads, session channels, non-determinism, and exceptions.