ECOOP 2020
Sun 15 - Tue 17 November 2020 Online Conference
co-located with SPLASH 2020
Sun 15 Nov 2020 21:40 - 22:00 at SPLASH-I - S-2 Chair(s): Atsushi Igarashi, Hidehiko Masuhara
Sun 15 Nov 2020 09:40 - 10:00 at SPLASH-I - S-2 Chair(s): Yu David Liu, Shigeru Chiba

Multiple modern programming languages, including Kotlin, Scala, Swift, and C#, have type systems where nullability is explicitly specified in the types. All of the above also need to interoperate with languages where types remain implicitly nullable, like Java. This leads to runtime errors that can manifest in subtle ways. In this paper, we show how to reason about the presence and provenance of such nullability errors using the concept of blame from gradual typing. Specifically, we introduce a calculus LambdaNull, where some terms are typed as implicitly nullable and others as explicitly nullable. Just like in the original blame calculus of Wadler and Findler, interactions between both kinds of terms are mediated by casts with attached blame labels, which indicate the origin of errors. On top of LambdaNull, we then define a second calculus, StratifiedLambdaNull, which closely models the interoperability between languages with implicit nullability and languages with explicit nullability, such as Java and Scala. Our main result is a theorem that states that nullability errors in StratifiedLambdaNull can always be blamed on terms with less-precise typing; that is, terms typed as implicitly nullable. By analogy, this would mean that NullPointerExceptions in combined Java/Scala programs are always the result of unsoundness in the Java type system. We summarize our result with the slogan explicitly nullable programs can’t be blamed. All our results are formalized in the Coq proof assistant.

Sun 15 Nov
Times are displayed in time zone: Central Time (US & Canada) change

09:00 - 10:20: S-2Research Papers at SPLASH-I +12h
Chair(s): Yu David LiuState University of New York (SUNY) Binghamton, Shigeru ChibaThe University of Tokyo
09:00 - 09:20
Talk
Research Papers
Matías ToroUniversity of Chile, Éric TanterUniversity of Chile
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09:20 - 09:40
Talk
Research Papers
Lukas DiekmannKing's College London, Laurence TrattKing's College London
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09:40 - 10:00
Talk
Research Papers
Abel NietoAarhus University, Marianna RapoportUniversity of Waterloo, Gregor RichardsUniversity of Waterloo, Ondřej LhotákUniversity of Waterloo
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10:00 - 10:20
Talk
Research Papers
Hila PelegUniversity of California at San Diego, Nadia PolikarpovaUniversity of California at San Diego
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21:00 - 22:20: S-2Research Papers at SPLASH-I
Chair(s): Atsushi IgarashiKyoto University, Japan, Hidehiko MasuharaTokyo Institute of Technology
21:00 - 21:20
Talk
Research Papers
Matías ToroUniversity of Chile, Éric TanterUniversity of Chile
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21:20 - 21:40
Talk
Research Papers
Lukas DiekmannKing's College London, Laurence TrattKing's College London
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21:40 - 22:00
Talk
Research Papers
Abel NietoAarhus University, Marianna RapoportUniversity of Waterloo, Gregor RichardsUniversity of Waterloo, Ondřej LhotákUniversity of Waterloo
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22:00 - 22:20
Talk
Research Papers
Hila PelegUniversity of California at San Diego, Nadia PolikarpovaUniversity of California at San Diego
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