22 research outputs found
Tor: modular search with hookable disjunction
Horn Clause Programs have a natural exhaustive depth-first procedural semantics. However, for many programs this semantics is ineffective. In order to compute useful solutions, one needs the ability to modify the search method that explores the alternative execution branches.
Tor, a well-defined hook into Prolog disjunction, provides this ability. It is light-weight thanks to its library approach. Tor supports modular composition of search methods and other hooks. The Tor library is already provided and used as an add-on to SWI-Prolog
Integrating Datalog and Constraint Solving
LP is a common formalism for the field of databases and CSP, both at the
theoretical level and the implementation level in the form of Datalog and CLP.
In the past, close correspondences have been made between both fields at the
theoretical level. Yet correspondence at the implementation level has been much
less explored. In this article we work towards relating them at the
implementation level. Concretely, we show how to derive the efficient Leapfrog
Triejoin execution algorithm of Datalog from a generic CP execution scheme.Comment: Proceedings of the 13th International Colloquium on Implementation of
Constraint LOgic Programming Systems (CICLOPS 2013), Istanbul, Turkey, August
25, 201
Tabling as a Library with Delimited Control
Tabling is probably the most widely studied extension of Prolog. But despite
its importance and practicality, tabling is not implemented by most Prolog
systems. Existing approaches require substantial changes to the Prolog engine,
which is an investment out of reach of most systems. To enable more widespread
adoption, we present a new implementation of tabling in under 600 lines of
Prolog code. Our lightweight approach relies on delimited control and provides
reasonable performance.Comment: 15 pages. To appear in Theory and Practice of Logic Programming
(TPLP), Proceedings of ICLP 201
TOR: modular search with hookable disjunction
Horn Clause Programs have a natural exhaustive depth-first procedural
semantics. However, for many programs this semantics is
ineffective. In order to compute useful solutions, one needs the
ability to modify the search method that explores the alternative
execution branches.
Tor, a well-defined hook into Prolog disjunction, provides this ability.
It is light-weight thanks to its library approach and efficient
because it is based on program transformation.
Tor is general enough to mimic search-modifying
predicates like ECLiPSe's search/6. Moreover, Tor supports
modular composition of search methods and other hooks.
The Tor library is already
provided and used as an add-on to SWI-Prolog.publisher: Elsevier
articletitle: Tor: Modular search with hookable disjunction
journaltitle: Science of Computer Programming
articlelink: http://dx.doi.org/10.1016/j.scico.2013.05.008
content_type: article
copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe
Tabling with Sound Answer Subsumption
Tabling is a powerful resolution mechanism for logic programs that captures
their least fixed point semantics more faithfully than plain Prolog. In many
tabling applications, we are not interested in the set of all answers to a
goal, but only require an aggregation of those answers. Several works have
studied efficient techniques, such as lattice-based answer subsumption and
mode-directed tabling, to do so for various forms of aggregation.
While much attention has been paid to expressivity and efficient
implementation of the different approaches, soundness has not been considered.
This paper shows that the different implementations indeed fail to produce
least fixed points for some programs. As a remedy, we provide a formal
framework that generalises the existing approaches and we establish a soundness
criterion that explains for which programs the approach is sound.
This article is under consideration for acceptance in TPLP.Comment: Paper presented at the 32nd International Conference on Logic
Programming (ICLP 2016), New York City, USA, 16-21 October 2016, 15 pages,
LaTeX, 0 PDF figure
Delimited continuations for Prolog
Delimited continuations are a famous control primitive that originates in the functional programming world. It allows the programmer to suspend and capture the remaining part of a computation in order to resume it later. We put a new Prolog-compatible face on this primitive and specify its semantics by means of a meta-interpreter. Moreover, we establish the power of delimited continuations in Prolog with several example definitions of high-level language features. Finally, we show how to easily and effectively add delimited continuations support to the WAM
Delimited continuations in Prolog: semantics, use, and implementation in the WAM
An implementation of a delimited continuations, known in the functional programming world, is shown in the context of the WAM, and more particular in hProlog. Three new predicates become available to the user: reset/3 and shift/1 for delimiting and capturing the continuation, and call continuation/1 for calling it. The underlying low-level built-ins and modifications to the system are described in detail. While these do not turn continuations into first-class Prolog citizens, their usefulness is shown in a series of examples. The idea behind this implementation can be adapted to other Prolog implementations. The constructs are compared with similar ones in BinProlog and Haskell. Their interaction with other parts of Prolog is discussed
Implementing LP systems with CP techniques
This article gives an overview of my research activities since October 2012. It discusses various areas of logic programming with constraint programming as a common denominator