405,372 research outputs found
Foundations for structured programming with GADTs
GADTs are at the cutting edge of functional programming and become more widely used every day. Nevertheless, the semantic foundations underlying GADTs are not well understood. In this paper we solve this problem by showing that the standard theory of data types as carriers of initial algebras of functors can be extended from algebraic and nested data types to GADTs. We then use this observation to derive an initial algebra semantics for GADTs, thus ensuring that all of the accumulated knowledge about initial algebras can be brought to bear on them. Next, we use our initial algebra semantics for GADTs to derive expressive and principled tools — analogous to the well-known and widely-used ones for algebraic and nested data types — for reasoning about, programming with, and improving the performance of programs involving, GADTs; we christen such a collection of tools for a GADT an initial algebra package. Along the way, we give a constructive demonstration that every GADT can be reduced to one which uses only the equality GADT and existential quantification. Although other such reductions exist in the literature, ours is entirely local, is independent of any particular syntactic presentation of GADTs, and can be implemented in the host language, rather than existing solely as a metatheoretical artifact. The main technical ideas underlying our approach are (i) to modify the notion of a higher-order functor so that GADTs can be seen as carriers of initial algebras of higher-order functors, and (ii) to use left Kan extensions to trade arbitrary GADTs for simpler-but-equivalent ones for which initial algebra semantics can be derive
Exhibition Structural Point: Structures Construction Mock-Ups
The exhibition "STRUCTURAL POINT: Structures Construction Mock-Ups” shows a special emphasis on building structures. This exhibition is made up of 50 detailed mock-ups that show every constructive element, joints and specific details in buildings, where different types of materials (metal, wood and reinforced concrete) have been used. This work has been made by the students of the Building Engineering Degree, as a main exercise in the subjects called “Structures Construction I and II”. Moreover, this activity has been complemented by parallel events during its exposure time at the Museum of the University of Alicante in order to open the degree at a university level, using the exhibition as a meeting point of leading professionals, important specialized construction companies and also, as a promotion of the degree for prospective college students. Finally, it is important to consider that many different elements related with constructive techniques play a key role in the building process: the best construction systems must be used, the most efficient solutions must be considered and the materials must be chosen carefully. All these concepts are basic to be included in the exhibition as they consider essential topics in the field of construction for the students of the degree in the Polytechnic School. In conclusion, the realization of this exhibition has served as global meeting point for students, professionals and future college students
On Constructive Axiomatic Method
In this last version of the paper one may find a critical overview of some
recent philosophical literature on Axiomatic Method and Genetic Method.Comment: 25 pages, no figure
Towards a constructive simplicial model of Univalent Foundations
We provide a partial solution to the problem of defining a constructive
version of Voevodsky's simplicial model of univalent foundations. For this, we
prove constructive counterparts of the necessary results of simplicial homotopy
theory, building on the constructive version of the Kan-Quillen model structure
established by the second-named author. In particular, we show that dependent
products along fibrations with cofibrant domains preserve fibrations, establish
the weak equivalence extension property for weak equivalences between
fibrations with cofibrant domain and define a univalent classifying fibration
for small fibrations between bifibrant objects. These results allow us to
define a comprehension category supporting identity types, -types,
-types and a univalent universe, leaving only a coherence question to be
addressed.Comment: v3: changed the definition of the type Weq(U) of weak equivalences to
fix a problem with constructivity. Other Minor changes. 31 page
Constructive set theory and Brouwerian principles
The paper furnishes realizability models of constructive Zermelo-Fraenkel set theory, CZF, which also validate Brouwerian principles such as the axiom of continuous choice (CC), the fan theorem (FT), and monotone bar induction (BIM), and thereby determines the proof-theoretic strength of CZF augmented by these principles. The upshot is that CZF+CC+FT possesses the same strength as CZF, or more precisely, that CZF+CC+FTis conservative over CZF for 02 statements of arithmetic, whereas the addition of a restricted version of bar induction to CZF (called decidable bar induction, BID) leads to greater proof-theoretic strength in that CZF+BID proves the consistency of CZF
A realizability semantics for inductive formal topologies, Church's Thesis and Axiom of Choice
We present a Kleene realizability semantics for the intensional level of the
Minimalist Foundation, for short mtt, extended with inductively generated
formal topologies, Church's thesis and axiom of choice. This semantics is an
extension of the one used to show consistency of the intensional level of the
Minimalist Foundation with the axiom of choice and formal Church's thesis in
previous work. A main novelty here is that such a semantics is formalized in a
constructive theory represented by Aczel's constructive set theory CZF extended
with the regular extension axiom
Linear logic for constructive mathematics
We show that numerous distinctive concepts of constructive mathematics arise
automatically from an interpretation of "linear higher-order logic" into
intuitionistic higher-order logic via a Chu construction. This includes
apartness relations, complemented subsets, anti-subgroups and anti-ideals,
strict and non-strict order pairs, cut-valued metrics, and apartness spaces. We
also explain the constructive bifurcation of classical concepts using the
choice between multiplicative and additive linear connectives. Linear logic
thus systematically "constructivizes" classical definitions and deals
automatically with the resulting bookkeeping, and could potentially be used
directly as a basis for constructive mathematics in place of intuitionistic
logic.Comment: 39 page
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