ICFP 2017
Sun 3 - Sat 9 September 2017 Oxford, United Kingdom
Wed 6 Sep 2017 11:15 - 11:37 at L1 - Dependently Typed Programming Chair(s): Dan Licata

Sized types have been developed to make termination checking more perspicuous, more powerful, and more modular by integrating termination into type checking. In dependently-typed proof assistants where proofs by induction are just recursive functional programs, the termination checker is an integral component of the trusted core, as validity of proofs depend on termination. However, a rigorous integration of full-fledged sized types into dependent type theory is lacking so far. Such an integration is non-trivial, as explicit sizes in proof terms might get in the way of equality checking, making terms appear distinct that should have the same semantics.

In this article, we integrate dependent types and sized types with higher-rank size polymorphism, which is essential for generic programming and abstraction. We introduce a size quantifier $\forall$ which lets us ignore sizes in terms for equality checking, alongside with a second quantifier $\Pi$ for abstracting over sizes that do affect the semantics of types and terms. Judgmental equality is decided by an adaptation of normalization-by-evaluation for our new type theory, which features \emph{type shape}-directed reflection and reification. It follows that subtyping and type checking of normal forms are decidable as well, the latter by a bidirectional algorithm.

#### Wed 6 Sep

 10:30 - 12:00: Research Papers - Dependently Typed Programming at L1 Chair(s): Dan LicataWesleyan University 10:30 - 10:52Talk A Specification for Dependent Types in HaskellStephanie WeirichUniversity of Pennsylvania, USA, Antoine VoizardUniversity of Pennsylvania, USA, Pedro Henrique Azevedo de AmorimEcole Polytechnique, n.n. / University of Campinas, Brazil, Richard A. EisenbergBryn Mawr College, USA DOI 10:52 - 11:15Talk Parametric Quantifiers for Dependent Type TheoryAndreas NuytsKU Leuven, Belgium, Andrea VezzosiChalmers University of Technology, Sweden, Dominique DevrieseKU Leuven, Belgium DOI 11:15 - 11:37Talk Normalization by Evaluation for Sized Dependent TypesAndreas AbelUniversity of Gothenburg, Sweden, Andrea VezzosiChalmers University of Technology, Sweden, Theo WinterhalterENS Paris-Saclay, France DOI 11:37 - 12:00Talk A Metaprogramming Framework for Formal VerificationGabriel EbnerVienna University of Technology, Austria, Sebastian UllrichKIT, Germany, Jared RoeschUniversity of Washington, USA, Jeremy AvigadCarnegie Mellon University, USA, Leonardo De MouraMicrosoft Research, n.n. DOI