Synthetic domain theory in type theory: Another logic of computable functions

1996 ◽  
pp. 363-380 ◽  
Author(s):  
Bernhard Reus
Keyword(s):  
Type Theory ◽  
Domain Theory ◽  
Computable Functions

General synthetic domain theory – a logical approach

1999 ◽  
Vol 9 (2) ◽  
pp. 177-223 ◽  
Author(s):  
BERNHARD REUS ◽  
THOMAS STREICHER
Keyword(s):  
Type Theory ◽  
Function Spaces ◽  
Basic Type ◽  
Domain Theory ◽  
Stable Domain ◽  
Constructive Type Theory ◽  
Logical Language ◽  
Core Theory ◽  
Stable Domains ◽  
Rule Out

Synthetic domain theory (SDT) is a version of Domain Theory where ‘all functions are continuous’. Following the original suggestion of Dana Scott, several approaches to SDT have been developed that are logical or categorical, axiomatic or model-oriented in character and that are either specialised towards Scott domains or aim at providing a general theory axiomatising the structure common to the various notions of domains studied so far.In Reus and Streicher (1993), Reus (1995) and Reus (1998), we have developed a logical and axiomatic version of SDT, which is special in the sense that it captures the essence of Domain Theory à la Scott but rules out, for example, Stable Domain Theory, as it requires order on function spaces to be pointwise. In this article we will give a logical and axiomatic account of a general SDT with the aim of grasping the structure common to all notions of domains.As in loc.cit., the underlying logic is a sufficiently expressive version of constructive type theory. We start with a few basic axioms giving rise to a core theory on top of which we study various notions of predomains (such as, for example, complete and well-complete S-spaces (Longley and Simpson 1997)), define the appropriate notion of domain and verify the usual induction principles of domain theory.Although each domain carries a logically definable ‘specialization order’, we avoid order-theoretic notions as much as possible in the formulation of axioms and theorems. The reason is that the order on function spaces cannot be required to be pointwise, as this would rule out the model of stable domains à la Berry.The consequent use of logical language – understood as the internal language of some categorical model of type theory – avoids the irritating coexistence of the internal and the external view pervading purely categorical approaches. Therefore, the paper is aimed at providing an elementary introduction to synthetic domain theory, albeit requiring some knowledge of basic type theory.

HOLCF = HOL + LCF

1999 ◽  
Vol 9 (2) ◽  
pp. 191-223 ◽  
Author(s):  
OLAF MÜLLER ◽  
TOBIAS NIPKOW ◽  
DAVID VON OHEIMB ◽  
OSCAR SLOTOSCH
Keyword(s):  
Functional Programming ◽  
Denotational Semantics ◽  
Order Logic ◽  
Domain Theory ◽  
Theorem Prover ◽  
Higher Order Logic ◽  
Computable Functions ◽  
Recursive Domain Equations ◽  
Standard Domain ◽  
Definitional Extension

HOLCF is the definitional extension of Church's Higher-Order Logic with Scott's Logic for Computable Functions that has been implemented in the theorem prover Isabelle. This results in a flexible setup for reasoning about functional programs. HOLCF supports standard domain theory (in particular fixpoint reasoning and recursive domain equations), but also coinductive arguments about lazy datatypes. This paper describes in detail how domain theory is embedded in HOL, and presents applications from functional programming, concurrency and denotational semantics.

scholarly journals Denotational semantics of recursive types in synthetic guarded domain theory

2018 ◽  
Vol 29 (3) ◽  
pp. 465-510 ◽  
Author(s):  
RASMUS E. MØGELBERG ◽  
MARCO PAVIOTTI
Keyword(s):  
Programming Languages ◽  
Type Theory ◽  
Operational Semantics ◽  
Lambda Calculus ◽  
Denotational Semantics ◽  
Domain Theory ◽  
Logical Relation ◽  
Dependent Type Theory ◽  
Semantics Of Programming Languages ◽  
Dependent Type

Just like any other branch of mathematics, denotational semantics of programming languages should be formalised in type theory, but adapting traditional domain theoretic semantics, as originally formulated in classical set theory to type theory has proven challenging. This paper is part of a project on formulating denotational semantics in type theories with guarded recursion. This should have the benefit of not only giving simpler semantics and proofs of properties such as adequacy, but also hopefully in the future to scale to languages with advanced features, such as general references, outside the reach of traditional domain theoretic techniques.Working inGuarded Dependent Type Theory(GDTT), we develop denotational semantics for Fixed Point Calculus (FPC), the simply typed lambda calculus extended with recursive types, modelling the recursive types of FPC using the guarded recursive types ofGDTT. We prove soundness and computational adequacy of the model inGDTTusing a logical relation between syntax and semantics constructed also using guarded recursive types. The denotational semantics is intensional in the sense that it counts the number of unfold-fold reductions needed to compute the value of a term, but we construct a relation relating the denotations of extensionally equal terms, i.e., pairs of terms that compute the same value in a different number of steps. Finally, we show how the denotational semantics of terms can be executed inside type theory and prove that executing the denotation of a boolean term computes the same value as the operational semantics of FPC.

Hyperfinite type structures

1999 ◽  
Vol 64 (3) ◽  
pp. 1216-1242 ◽  
Author(s):  
Dag Normann ◽  
Erik Palmgren ◽  
Viggo Stoltenberg-Hansen
Keyword(s):  
Mathematical Model ◽  
Type Theory ◽  
Nonstandard Analysis ◽  
A Priori ◽  
Domain Theory ◽  
Transfer Principle ◽  
Finitely Based ◽  
Constructive Version ◽  
Continuous Functionals ◽  
Original Concept

The notion of a hyperfinite set comes from nonstandard analysis. Such a set has the internal cardinality of a nonstandard natural number. By a transfer principle such sets share many properties of finite sets. Here we apply this notion to give a hyperfinite model of the Kleene-Kreisel continuous functionals. We also extend the method to provide a hyperfinite characterisation of certain transfinite type structures, thus, through the work of Waagbø [14], constructing a hyperfinite model for Martin-Löf type theory.This kind of application is not new. Normann [6] gave a characterisation of the Kleene-Kreisel continuous functionals using ‘hyperfinitary’ functionals. The novelty here is that we use a constructive version of hyperfinite functionals and also generalise the method to transfinite types. Many of the results of this paper are constructive, though not the characterisation theorems themselves.Our characterisation of the Kleene-Kreisel continuous functionals is a supplement to a number of previous characterisations of topological and recursion-theoretical nature, see [6] for a brief survey. Altogether these characterisations show that the original concept of Kleene and Kreisel forms the correct mathematical model of the idea of finitely based functions of finite types.There is, however, no a priori reason to believe that there is a canonical way to extend the continuous functionals to cover transfinite objects of transfinite type used in, e.g., type theory. Our characterisation of Waagbø's model indicates that the model is natural, not only seen from domain theory but from a higher perspective. Normann and Waagbø (unpublished) have subsequently obtained a limit-space characterisation that further supports this view.

scholarly journals Representing Continuous Functions between Greatest Fixed Points of Indexed Containers

2021 ◽  
Vol Volume 17, Issue 3 ◽  
Author(s):  
Pierre Hyvernat
Keyword(s):  
Fixed Points ◽  
Type Theory ◽  
Continuous Functions ◽  
Dependent Type Theory ◽  
Recursive Definitions ◽  
Computable Functions ◽  
Dependent Type

We describe a way to represent computable functions between coinductive types as particular transducers in type theory. This generalizes earlier work on functions between streams by P. Hancock to a much richer class of coinductive types. Those transducers can be defined in dependent type theory without any notion of equality but require inductive-recursive definitions. Most of the properties of these constructions only rely on a mild notion of equality (intensional equality) and can thus be formalized in the dependently typed language Agda.

Basic Simple Type Theory

1997 ◽  
Author(s):  
J. Roger Hindley
Keyword(s):  
Type Theory ◽  
Simple Type ◽  
Simple Type Theory

Type Theory and Formal Proof

2009 ◽  
Author(s):  
Rob Nederpelt ◽  
Herman Geuvers
Keyword(s):  
Type Theory ◽  
Formal Proof
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