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POPL 2021
Sun 17 - Fri 22 January 2021 Online
Thu 21 Jan 2021 19:00 - 19:10 at POPL-B - Types and Functional Languages

Randomized higher-order computation can be seen as being captured by a λ-calculus endowed with a single algebraic operation, namely a construct for binary probabilistic choice. What matters about such computations is the probability of obtaining any given result, rather than the possibility or the necessity of obtaining it, like in (non)deterministic computation. Termination, arguably the simplest kind of reachability problem, can be spelled out in at least two ways, depending on whether it talks about the probability of convergence or about the expected evaluation time, the second one providing a stronger guarantee. In this paper, we show that intersection types are capable of precisely characterizing both notions of termination inside a single system of types: the probability of convergence of any λ-term can be underapproximated by its type, while the underlying derivation’s weight gives a lower bound to the term’s expected number of steps to normal form. Noticeably, both approximations are tight—not only soundness but also completeness holds. The crucial ingredient is non-idempotency, without which it would be impossible to reason on the expected number of reduction steps which are necessary to completely evaluate any term. Besides, the kind of approximation we obtain is proved to be \emph{optimal} recursion theoretically: no recursively enumerable formal system can do better than that.

Thu 21 Jan

Displayed time zone: Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna change

18:30 - 19:30
Types and Functional LanguagesPOPL at POPL-B
18:30
10m
Talk
Diamonds Are Not Forever: Liveness in Reactive Programming with Guarded Recursion
POPL
Patrick Bahr IT University of Copenhagen, Christian Uldal Graulund IT University of Copenhagen, Rasmus Ejlers Møgelberg IT University of Copenhagen
Link to publication DOI
18:40
10m
Talk
On the Semantic Expressiveness of Recursive Types
POPL
Marco Patrignani Stanford University, USA / CISPA, Germany, Eric Mark Martin Stanford, Dominique Devriese Vrije Universiteit Brussel
Link to publication DOI
18:50
10m
Talk
Automatic Differentiation in PCF
POPL
Damiano Mazza CNRS, Michele Pagani IRIF - Université de Paris
Link to publication DOI Pre-print
19:00
10m
Talk
Intersection Types and (Positive) Almost-Sure Termination
POPL
Ugo Dal Lago University of Bologna, Italy / Inria, France, Claudia Faggian Université de Paris & CNRS, Simona Ronchi Della Rocca University of Torino
Link to publication DOI
19:10
10m
Talk
Intensional Datatype Refinement
POPL
Eddie Jones University of Bristol, Steven Ramsay University of Bristol
Link to publication DOI
19:20
10m
Talk
Abstracting Gradual Typing Moving Forward : Precise and Space-Efficient
POPL
Felipe Bañados Schwerter University of British Columbia, Alison M. Clark University of British Columbia, Khurram A. Jafery University of British Columbia, Ronald Garcia University of British Columbia
Link to publication DOI