Cubical Agda: A dependently typed programming language with univalence and higher inductive types

2021 ◽  
Vol 31 ◽  
Author(s):  
ANDREA VEZZOSI ◽  
ANDERS MÖRTBERG ◽  
ANDREAS ABEL
Keyword(s):  
Programming Language ◽  
Type Theory ◽  
Type Checking ◽  
Dependent Type Theory ◽  
Wide Range ◽  
General Schema ◽  
Direct Definition ◽  
Inductive Types ◽  
Definition Of ◽  
Cubical Type Theory

Abstract Proof assistants based on dependent type theory provide expressive languages for both programming and proving within the same system. However, all of the major implementations lack powerful extensionality principles for reasoning about equality, such as function and propositional extensionality. These principles are typically added axiomatically which disrupts the constructive properties of these systems. Cubical type theory provides a solution by giving computational meaning to Homotopy Type Theory and Univalent Foundations, in particular to the univalence axiom and higher inductive types (HITs). This paper describes an extension of the dependently typed functional programming language Agda with cubical primitives, making it into a full-blown proof assistant with native support for univalence and a general schema of HITs. These new primitives allow the direct definition of function and propositional extensionality as well as quotient types, all with computational content. Additionally, thanks also to copatterns, bisimilarity is equivalent to equality for coinductive types. The adoption of cubical type theory extends Agda with support for a wide range of extensionality principles, without sacrificing type checking and constructivity.

Algebra of programming in Agda: Dependent types for relational program derivation

2009 ◽  
Vol 19 (5) ◽  
pp. 545-579 ◽  
Author(s):  
SHIN-CHENG MU ◽  
HSIANG-SHANG KO ◽  
PATRIK JANSSON
Keyword(s):  
Programming Language ◽  
Type Theory ◽  
Type System ◽  
Dependent Types ◽  
Dependent Type Theory ◽  
Program Derivation ◽  
Inductive Types ◽  
Algebra Of Programming ◽  
Dependent Type

AbstractRelational program derivation is the technique of stepwise refining a relational specification to a program by algebraic rules. The program thus obtained is correct by construction. Meanwhile, dependent type theory is rich enough to express various correctness properties to be verified by the type checker. We have developed a library, AoPA (Algebra of Programming in Agda), to encode relational derivations in the dependently typed programming language Agda. A program is coupled with an algebraic derivation whose correctness is guaranteed by the type system. Two non-trivial examples are presented: an optimisation problem and a derivation of quicksort in which well-founded recursion is used to model terminating hylomorphisms in a language with inductive types.

Idris, a general-purpose dependently typed programming language: Design and implementation

2013 ◽  
Vol 23 (5) ◽  
pp. 552-593 ◽  
Author(s):  
EDWIN BRADY
Keyword(s):  
Programming Language ◽  
Type Theory ◽  
Functional Programming ◽  
General Purpose ◽  
High Level Language ◽  
Type Checking ◽  
Programming Language Design ◽  
Implicit Arguments ◽  
Type Classes ◽  
High Level

AbstractMany components of a dependently typed programming language are by now well understood, for example, the underlying type theory, type checking, unification and evaluation. How to combine these components into a realistic and usable high-level language is, however, folklore, discovered anew by successive language implementors. In this paper, I describe the implementation ofIdris, a new dependently typed functional programming language.Idrisis intended to be ageneral-purposeprogramming language and as such provides high-level concepts such as implicit syntax, type classes anddonotation. I describe the high-level language and the underlying type theory, and present a tactic-based method forelaboratingconcrete high-level syntax with implicit arguments and type classes into a fully explicit type theory. Furthermore, I show how this method facilitates the implementation of new high-level language constructs.

scholarly journals Univalent categories and the Rezk completion

2015 ◽  
Vol 25 (5) ◽  
pp. 1010-1039 ◽  
Author(s):  
BENEDIKT AHRENS ◽  
KRZYSZTOF KAPULKIN ◽  
MICHAEL SHULMAN
Keyword(s):  
Category Theory ◽  
Type Theory ◽  
Dependent Type Theory ◽  
Equivalence Of Categories ◽  
Segal Spaces ◽  
Definition Of ◽  
Categorical Semantics ◽  
Univalent Foundations ◽  
Dependent Type

We develop category theory within Univalent Foundations, which is a foundational system for mathematics based on a homotopical interpretation of dependent type theory. In this system, we propose a definition of ‘category’ for which equality and equivalence of categories agree. Such categories satisfy a version of the univalence axiom, saying that the type of isomorphisms between any two objects is equivalent to the identity type between these objects; we call them ‘saturated’ or ‘univalent’ categories. Moreover, we show that any category is weakly equivalent to a univalent one in a universal way. In homotopical and higher-categorical semantics, this construction corresponds to a truncated version of the Rezk completion for Segal spaces, and also to the stack completion of a prestack.

scholarly journals Graded Modal Dependent Type Theory

2021 ◽  
pp. 462-490
Author(s):  
Benjamin Moon ◽  
Harley Eades III ◽  
Dominic Orchard
Keyword(s):  
Case Studies ◽  
Type Theory ◽  
Data Use ◽  
Type Checking ◽  
Fine Grained ◽  
Dependent Type Theory ◽  
Checking Procedure ◽  
Dependent Type

AbstractGraded type theories are an emerging paradigm for augmenting the reasoning power of types with parameterizable, fine-grained analyses of program properties. There have been many such theories in recent years which equip a type theory with quantitative dataflow tracking, usually via a semiring-like structure which provides analysis on variables (often called ‘quantitative’ or ‘coeffect’ theories). We present Graded Modal Dependent Type Theory (Grtt for short), which equips a dependent type theory with a general, parameterizable analysis of the flow of data, both in and between computational terms and types. In this theory, it is possible to study, restrict, and reason about data use in programs and types, enabling, for example, parametric quantifiers and linearity to be captured in a dependent setting. We propose Grtt, study its metatheory, and explore various case studies of its use in reasoning about programs and studying other type theories. We have implemented the theory and highlight the interesting details, including showing an application of grading to optimising the type checking procedure itself.

Modelling general recursion in type theory

2005 ◽  
Vol 15 (4) ◽  
pp. 671-708 ◽  
Author(s):  
ANA BOVE ◽  
VENANZIO CAPRETTA
Keyword(s):  
Programming Language ◽  
Type Theory ◽  
Functional Programming ◽  
Recursive Algorithm ◽  
Recursive Algorithms ◽  
Constructive Type Theory ◽  
Structural Recursion ◽  
Constructive Type ◽  
Definition Of ◽  
Theoretic Version

Constructive type theory is an expressive programming language in which both algorithms and proofs can be represented. A limitation of constructive type theory as a programming language is that only terminating programs can be defined in it. Hence, general recursive algorithms have no direct formalisation in type theory since they contain recursive calls that satisfy no syntactic condition guaranteeing termination. In this work, we present a method to formalise general recursive algorithms in type theory. Given a general recursive algorithm, our method is to define an inductive special-purpose accessibility predicate that characterises the inputs on which the algorithm terminates. The type-theoretic version of the algorithm is then defined by structural recursion on the proof that the input values satisfy this predicate. The method separates the computational and logical parts of the definitions and thus the resulting type-theoretic algorithms are clear, compact and easy to understand. They are as simple as their equivalents in a functional programming language, where there is no restriction on recursive calls. Here, we give a formal definition of the method and discuss its power and its limitations.

scholarly journals Internal Parametricity for Cubical Type Theory

2021 ◽  
Vol Volume 17, Issue 4 ◽  
Author(s):  
Evan Cavallo ◽  
Robert Harper
Keyword(s):  
Type Theory ◽  
Formal Interface ◽  
Inductive Types ◽  
Cubical Type Theory

We define a computational type theory combining the contentful equality structure of cartesian cubical type theory with internal parametricity primitives. The combined theory supports both univalence and its relational equivalent, which we call relativity. We demonstrate the use of the theory by analyzing polymorphic functions between higher inductive types, observe how cubical equality regularizes parametric type theory, and examine the similarities and discrepancies between cubical and parametric type theory, which are closely related. We also abstract a formal interface to the computational interpretation and show that this also has a presheaf model.

Intuitionistic ancestral logic

2019 ◽  
Vol 29 (4) ◽  
pp. 469-486 ◽  
Author(s):  
Liron Cohen ◽  
Robert L Constable
Keyword(s):  
Programming Language ◽  
Type Theory ◽  
Transitive Closure ◽  
Order Logic ◽  
First Order Logic ◽  
First Order ◽  
Constructive Type Theory ◽  
Programming Logic ◽  
Natural Type ◽  
Definition Of

Abstract In this article we define pure intuitionistic Ancestral Logic ( iAL ), extending pure intuitionistic First-Order Logic ( iFOL ). This logic is a dependently typed abstract programming language with computational functionality beyond iFOL given by its realizer for the transitive closure, TC . We derive this operator from the natural type theoretic definition of TC using intersection. We show that provable formulas in iAL are uniformly realizable, thus iAL is sound with respect to constructive type theory. We further show that iAL subsumes Kleene Algebras with tests and thus serves as a natural programming logic for proving properties of program schemes. We also extract schemes from proofs that iAL specifications are solvable.

scholarly journals Semantics of higher inductive types

2019 ◽  
Vol 169 (1) ◽  
pp. 159-208 ◽  
Author(s):  
PETER LEFANU LUMSDAINE ◽  
MICHAEL SHULMAN
Keyword(s):  
Type Theory ◽  
Homotopy Theory ◽  
Model Category ◽  
Suitable Model ◽  
Simplicial Sets ◽  
James Construction ◽  
Quillen Model Category ◽  
Wide Range ◽  
Inductive Types ◽  
Cartesian Closed

AbstractHigher inductive typesare a class of type-forming rules, introduced to provide basic (and not-so-basic) homotopy-theoretic constructions in a type-theoretic style. They have proven very fruitful for the “synthetic” development of homotopy theory within type theory, as well as in formalising ordinary set-level mathematics in type theory. In this paper, we construct models of a wide range of higher inductive types in a fairly wide range of settings.We introduce the notion ofcell monad with parameters: a semantically-defined scheme for specifying homotopically well-behaved notions of structure. We then show that any suitable model category hasweakly stable typal initial algebrasfor any cell monad with parameters. When combined with the local universes construction to obtain strict stability, this specialises to give models of specific higher inductive types, including spheres, the torus, pushout types, truncations, the James construction and general localisations.Our results apply in any sufficiently nice Quillen model category, including any right proper, simplicially locally cartesian closed, simplicial Cisinski model category (such as simplicial sets) and any locally presentable locally cartesian closed category (such as sets) with its trivial model structure. In particular, any locally presentable locally cartesian closed (∞, 1)-category is presented by some model category to which our results apply.

scholarly journals Constructing Infinitary Quotient-Inductive Types

2020 ◽  
pp. 257-276
Author(s):  
Marcelo P. Fiore ◽  
Andrew M. Pitts ◽  
S. C. Steenkamp
Keyword(s):  
Type Theory ◽  
Theorem Prover ◽  
Dependent Type Theory ◽  
Inductive Definitions ◽  
Inductive Types ◽  
Recursive Definitions ◽  
Dependent Type

AbstractThis paper introduces an expressive class of quotient-inductive types, called QW-types. We show that in dependent type theory with uniqueness of identity proofs, even the infinitary case of QW-types can be encoded using the combination of inductive-inductive definitions involving strictly positive occurrences of Hofmann-style quotient types, and Abel’s size types. The latter, which provide a convenient constructive abstraction of what classically would be accomplished with transfinite ordinals, are used to prove termination of the recursive definitions of the elimination and computation properties of our encoding of QW-types. The development is formalized using the Agda theorem prover.

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