Algebra of constructions II: an algebraic approach to Martin-Löf type theory and the calculus of constructions

1993 ◽  
Vol 3 (1) ◽  
pp. 63-92
Author(s):  
Adam Obtułowicz
Keyword(s):  
Type Theory ◽  
Algebraic Theory ◽  
Algebraic Approach ◽  
Recursive Functions ◽  
Algebraic Theories ◽  
Calculus Of Constructions ◽  
Partial Algebras

We present an algebraic approach to the syntax and semantics of Martin-Löf type theory and the calculus of constructions developed by T. Coquand and G. Huet. In our approach, models of this theory and this calculus are treated as three-sorted partial algebras, called ITSΠ-structures, described by essentially algebraic theories. We give a proof that derived statements of Martin-Löf type theory hold in appropriate ITSΠ-structures. In this proof, a formal translation from the language of terms and types into the language of terms of an appropriate essentially algebraic theory of ITSΠ-structures is used. A straightforward set-theoretic construction of ITSΠ-structures that are models of Martin-Löf type theory is demonstrated. We present a construction of a recursive ITSΠ-structure(i.e. its partial and total operations are recursive functions over some alphabet) that is a model of the calculus of constructions and demonstrates the decidability of this calculus.

scholarly journals On generalized algebraic theories and categories with families

2021 ◽  
pp. 1-18
Author(s):  
Marc Bezem ◽  
Thierry Coquand ◽  
Peter Dybjer ◽  
Martín Escardó
Keyword(s):  
Type Theory ◽  
Algebraic Theory ◽  
Completeness Theorem ◽  
Small Category ◽  
Equational Logic ◽  
Algebraic Theories ◽  
Semantic Notion ◽  
Finitely Presented ◽  
Extra Structure

Abstract We give a syntax independent formulation of finitely presented generalized algebraic theories as initial objects in categories of categories with families (cwfs) with extra structure. To this end, we simultaneously define the notion of a presentation Σ of a generalized algebraic theory and the associated category CwFΣ of small cwfs with a Σ-structure and cwf-morphisms that preserve Σ-structure on the nose. Our definition refers to the purely semantic notion of uniform family of contexts, types, and terms in CwFΣ. Furthermore, we show how to syntactically construct an initial cwf with a Σ-structure. This result can be viewed as a generalization of Birkhoff’s completeness theorem for equational logic. It is obtained by extending Castellan, Clairambault, and Dybjer’s construction of an initial cwf. We provide examples of generalized algebraic theories for monoids, categories, categories with families, and categories with families with extra structure for some type formers of Martin-Löf type theory. The models of these are internal monoids, internal categories, and internal categories with families (with extra structure) in a small category with families. Finally, we show how to extend our definition to some generalized algebraic theories that are not finitely presented, such as the theory of contextual cwfs.

Algebraic Theory of Recombination Spaces

1997 ◽  
Vol 5 (3) ◽  
pp. 241-275 ◽  
Author(s):  
Peter F. Stadler ◽  
Günter P. Wagner
Keyword(s):  
Nearest Neighbor ◽  
Fitness Landscape ◽  
Algebraic Theory ◽  
Algebraic Approach ◽  
Search Space ◽  
Space Structure ◽  
Fitness Landscapes ◽  
Mathematical Representation ◽  
Laplacian Operator ◽  
Fourier Decomposition

A new mathematical representation is proposed for the configuration space structure induced by recombination, which we call “P-structure.” It consists of a mapping of pairs of objects to the power set of all objects in the search space. The mapping assigns to each pair of parental “genotypes” the set of all recombinant genotypes obtainable from the parental ones. It is shown that this construction allows a Fourier decomposition of fitness landscapes into a superposition of “elementary landscapes.” This decomposition is analogous to the Fourier decomposition of fitness landscapes on mutation spaces. The elementary landscapes are obtained as eigenfunctions of a Laplacian operator defined for P-structures. For binary string recombination, the elementary landscapes are exactly the p-spin functions (Walsh functions), that is, the same as the elementary landscapes of the string point mutation spaces (i.e., the hypercube). This supports the notion of a strong homomorphism between string mutation and recombination spaces. However, the effective nearest neighbor correlations on these elementary landscapes differ between mutation and recombination and among different recombination operators. On average, the nearest neighbor correlation is higher for one-point recombination than for uniform recombination. For one-point recombination, the correlations are higher for elementary landscapes with fewer interacting sites as well as for sites that have closer linkage, confirming the qualitative predictions of the Schema Theorem. We conclude that the algebraic approach to fitness landscape analysis can be extended to recombination spaces and provides an effective way to analyze the relative hardness of a landscape for a given recombination operator.

scholarly journals Large algebraic theories with small algebras

1978 ◽  
Vol 19 (3) ◽  
pp. 371-380 ◽  
Author(s):  
Jan Reiterman
Keyword(s):  
Algebraic Theory ◽  
Proper Class ◽  
Algebraic Theories

The aim of the paper is to study the interrelation between several natural smallness conditions on an algebraic theory with a proper class of operations. The conditions concern the existence of sets of data determining algebras, homomorphisms, subalgebras, and congruences.

scholarly journals FUNCTIONAL PEARL Unfolding pointer algorithms

2001 ◽  
Vol 11 (3) ◽  
pp. 347-358 ◽  
Author(s):  
RICHARD S. BIRD
Keyword(s):  
Formal Verification ◽  
Type Theory ◽  
Algebraic Approach ◽  
Functional Approach ◽  
Data Refinement ◽  
New Ideas ◽  
The Subject ◽  
Pointer Aliasing

A fair amount has been written on the subject of reasoning about pointer algorithms. There was a peak about 1980 when everyone seemed to be tackling the formal verification of the Schorr–Waite marking algorithm, including Gries (1979, Morris (1982) and Topor (1979). Bornat (2000) writes: “The Schorr–Waite algorithm is the first mountain that any formalism for pointer aliasing should climb”. Then it went more or less quiet for a while, but in the last few years there has been a resurgence of interest, driven by new ideas in relational algebras (Möeller, 1993), in data refinement Butler (1999), in type theory (Hofmann, 2000; Walker and Morrisett, 2000), in novel kinds of assertion (Reynolds, 2000), and by the demands of mechanised reasoning (Bornat, 2000). Most approaches end up being based in the Floyd–Dijkstra–Hoare tradition with loops and invariant assertions. To be sure, when dealing with any recursively-defined linked structure some declarative notation has to be brought in to specify the problem, but no one to my knowledge has advocated a purely functional approach throughout. Mason (1988) comes close, but his Lisp expressions can be very impure. Möller (1999) also exploits an algebraic approach, and the structure of his paper has much in common with what follows.This pearl explores the possibility of a simple functional approach to pointer manipulation algorithms.

AN ALGEBRAIC THEORY FOR REGULAR LANGUAGES OF FINITE AND INFINITE WORDS

1993 ◽  
Vol 03 (04) ◽  
pp. 447-489 ◽  
Author(s):  
THOMAS WILKE
Keyword(s):  
Algebraic Theory ◽  
Algebraic Approach ◽  
Regular Languages ◽  
Cantor Space ◽  
Infinite Words ◽  
Finite Semigroups ◽  
Borel Hierarchy ◽  
Algebraic Description ◽  
One To One

An algebraic approach to the theory of regular languages of finite and infinite words (∞-languages) is presented. It extends the algebraic theory of regular languages of finite words, which is based on finite semigroups. Their role is taken over by a structure called right binoid. A variety theorem is proved: there is a one-to-one correspondence between varieties of ∞-languages and pseudovarieties of right binoids. The class of locally threshold testable languages and several natural subclasses (such as the class of locally testable languages) as well as classes of the Borel hierarchy over the Cantor space (restricted to regular languages) are investigated as examples for varieties of ∞-languages. The corresponding pseudovarieties of right binoids are characterized and in some cases defining equations are derived. The connections with the algebraic description and classification of regular languages of infinite words in terms of finite semigroups are pointed out.

scholarly journals Primitive recursive algebraic theories and program schemes

1977 ◽  
Vol 17 (2) ◽  
pp. 207-233 ◽  
Author(s):  
W. Kühnel ◽  
J. Meseguer ◽  
M. Pfender ◽  
I. Sols
Keyword(s):  
Programming Language ◽  
Generation Process ◽  
Recursive Functions ◽  
Algebraic Theories ◽  
Primitive Recursion ◽  
Recursive Theory ◽  
Carry Over ◽  
Primitive Recursive

We introduce primitive recursion as a generation process for arrows of algebraic theories in the sense of Lawvere and carry over important results on algebraic theories and functorial semantics to the enriched setting of “primitive recursive algebra”: existence of free primitive recursive theories and of theories presented by operations and equations on primitive recursive functions; existence of free models presented by generators and equations. Finally semantical correctness of translations is reduced to correctness for the basic operations. There is a connection to the theory of program schemes: program schemes involving primitive recursion correspond to arrows of a primitive recursive theory freely generated over a graph of basic operations. This theory T can be viewed as a programming language with “arithmetics” given by the basic operations and with DO-loops. A machine loaded with a compiler for T can be interpreted as a T-model in Lawvere's sense, preserving primitive recursion.

scholarly journals Contextual modal types for algebraic effects and handlers

2021 ◽  
Vol 5 (ICFP) ◽  
pp. 1-29
Author(s):  
Nikita Zyuzin ◽  
Aleksandar Nanevski
Keyword(s):  
Programming Languages ◽  
Type Theory ◽  
Operational Semantics ◽  
Algebraic Theory ◽  
Type System ◽  
Effect Theory ◽  
Explicit Substitutions ◽  
Type And Effect Systems ◽  
Modal Type ◽  
Modal Types

Programming languages with algebraic effects often track the computations’ effects using type-and-effect systems. In this paper, we propose to view an algebraic effect theory of a computation as a variable context; consequently, we propose to track algebraic effects of a computation with contextual modal types . We develop ECMTT, a novel calculus which tracks algebraic effects by a contextualized variant of the modal □ (necessity) operator, that it inherits from Contextual Modal Type Theory (CMTT). Whereas type-and-effect systems add effect annotations on top of a prior programming language, the effect annotations in ECMTT are inherent to the language, as they are managed by programming constructs corresponding to the logical introduction and elimination forms for the □ modality. Thus, the type-and-effect system of ECMTT is actually just a type system. Our design obtains the properties of local soundness and completeness, and determines the operational semantics solely by β-reduction, as customary in other logic-based calculi. In this view, effect handlers arise naturally as a witness that one context (i.e., algebraic theory) can be reached from another, generalizing explicit substitutions from CMTT. To the best of our knowledge, ECMTT is the first system to relate algebraic effects to modal types. We also see it as a step towards providing a correspondence in the style of Curry and Howard that may transfer a number of results from the fields of modal logic and modal type theory to that of algebraic effects.

scholarly journals The costructure–cosemantics adjunction for comodels for computational effects

2021 ◽  
pp. 1-46
Author(s):  
Richard Garner
Keyword(s):  
Dynamic Properties ◽  
Algebraic Theory ◽  
The Other ◽  
Algebraic Theories ◽  
And Mathematics ◽  
The One ◽  
Suitable Environment ◽  
The Way

Abstract It is well established that equational algebraic theories and the monads they generate can be used to encode computational effects. An important insight of Power and Shkaravska is that comodels of an algebraic theory $\mathbb{T}$ – i.e., models in the opposite category $\mathcal{S}\mathrm{et}^{\mathrm{op}}$ – provide a suitable environment for evaluating the computational effects encoded by $\mathbb{T}$ . As already noted by Power and Shkaravska, taking comodels yields a functor from accessible monads to accessible comonads on $\mathcal{S}\mathrm{et}$ . In this paper, we show that this functor is part of an adjunction – the “costructure–cosemantics adjunction” of the title – and undertake a thorough investigation of its properties. We show that, on the one hand, the cosemantics functor takes its image in what we term the presheaf comonads induced by small categories; and that, on the other, costructure takes its image in the presheaf monads induced by small categories. In particular, the cosemantics comonad of an accessible monad will be induced by an explicitly-described category called its behaviour category that encodes the static and dynamic properties of the comodels. Similarly, the costructure monad of an accessible comonad will be induced by a behaviour category encoding static and dynamic properties of the comonad coalgebras. We tie these results together by showing that the costructure–cosemantics adjunction is idempotent, with fixpoints to either side given precisely by the presheaf monads and comonads. Along the way, we illustrate the value of our results with numerous examples drawn from computation and mathematics.

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