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Exceptional asynchronous session types: session types without tiers
Journal article   Open access

Exceptional asynchronous session types: session types without tiers

Simon Fowler, Sam Lindley, J. Garrett Morris and Sára Decova
Proceedings of ACM on programming languages, Vol.3(POPL), pp.1-29
01/02/2019
DOI: 10.1145/3290341
url
https://doi.org/10.1145/3290341View
Published (Version of record) Open Access

Abstract

Session types statically guarantee that communication complies with a protocol. However, most accounts of session typing do not account for failure, which means they are of limited use in real applications---especially distributed applications---where failure is pervasive. We present the first formal integration of asynchronous session types with exception handling in a functional programming language. We define a core calculus which satisfies preservation and progress properties, is deadlock free, confluent, and terminating. We provide the first implementation of session types with exception handling for a fully-fledged functional programming language, by extending the Links web programming language; our implementation draws on existing work on effect handlers. We illustrate our approach through a running example of two-factor authentication, and a larger example of a session-based chat application where communication occurs over session-typed channels and disconnections are handled gracefully.

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