86 research outputs found
Transforming floundering into success
We show how logic programs with "delays" can be transformed to programs
without delays in a way which preserves information concerning floundering
(also known as deadlock). This allows a declarative (model-theoretic),
bottom-up or goal independent approach to be used for analysis and debugging of
properties related to floundering. We rely on some previously introduced
restrictions on delay primitives and a key observation which allows properties
such as groundness to be analysed by approximating the (ground) success set.
This paper is to appear in Theory and Practice of Logic Programming (TPLP).
Keywords: Floundering, delays, coroutining, program analysis, abstract
interpretation, program transformation, declarative debuggingComment: Number of pages: 24 Number of figures: 9 Number of tables: non
Inferring Termination Conditions for Logic Programs using Backwards Analysis
This paper focuses on the inference of modes for which a logic program is
guaranteed to terminate. This generalises traditional termination analysis
where an analyser tries to verify termination for a specified mode. Our
contribution is a methodology in which components of traditional termination
analysis are combined with backwards analysis to obtain an analyser for
termination inference. We identify a condition on the components of the
analyser which guarantees that termination inference will infer all modes which
can be checked to terminate. The application of this methodology to enhance a
traditional termination analyser to perform also termination inference is
demonstrated
A generic persistence model for CLP systems (and two useful implementations)
This paper describes a model of persistence in (C)LP languages and two different and practically very useful ways to implement this model in current systems. The fundamental idea is that persistence is a characteristic of certain dynamic predicates (Le., those which encapsulate
state). The main effect of declaring a predicate persistent is that the dynamic changes made to such predicates persist from one execution to the next one. After proposing a syntax for declaring persistent predicates, a simple, file-based implementation of the concept is presented and
some examples shown. An additional implementation is presented which stores persistent predicates in an external datábase. The abstraction of the concept of persistence from its implementation allows developing applications
which can store their persistent predicates alternatively in files or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. The paper presents the model, the implementation approach in both the cases of using files
and relational databases, a number of optimizations of the process (using information obtained from static global analysis and goal clustering), and performance results from an implementation of these ideas
A Polyvariant Binding-Time Analysis for Off-line Partial Deduction
We study the notion of binding-time analysis for logic programs. We formalise
the unfolding aspect of an on-line partial deduction system as a Prolog
program. Using abstract interpretation, we collect information about the
run-time behaviour of the program. We use this information to make the control
decisions about the unfolding at analysis time and to turn the on-line system
into an off-line system. We report on some initial experiments.Comment: 19 pages (including appendix) Paper (without appendix) appeared in
Programming Languages and Systems, Proceedings of the European Symposium on
Programming (ESOP'98), Part of ETAPS'98 (Chris Hankin, eds.), LNCS, vol.
1381, 1998, pp. 27-4
On derived dependencies and connected databases
AbstractThis paper introduces a new class of deductive databases (connected databases) for which SLDNF-resolution never flounders and always computes ground answers. The class of connected databases properly includes that of allowed databases. Moreover the definition of connected databases enables evaluable predicates to be included in a uniform way. An algorithm is described which, for each predicate defined in a normal database, derives a propositional formula (groundness formula) describing dependencies between the arguments of that predicate. Groundness formulae are used to determine whether a database is connected. They are also used to identify goals for which SLDNF-resolution will never flounder and will always compute ground answers on a connected database
A Backward Analysis for Constraint Logic Programs
One recurring problem in program development is that of understanding how to
re-use code developed by a third party. In the context of (constraint) logic
programming, part of this problem reduces to figuring out how to query a
program. If the logic program does not come with any documentation, then the
programmer is forced to either experiment with queries in an ad hoc fashion or
trace the control-flow of the program (backward) to infer the modes in which a
predicate must be called so as to avoid an instantiation error. This paper
presents an abstract interpretation scheme that automates the latter technique.
The analysis presented in this paper can infer moding properties which if
satisfied by the initial query, come with the guarantee that the program and
query can never generate any moding or instantiation errors. Other applications
of the analysis are discussed. The paper explains how abstract domains with
certain computational properties (they condense) can be used to trace
control-flow backward (right-to-left) to infer useful properties of initial
queries. A correctness argument is presented and an implementation is reported.Comment: 32 page
RedAlert: Determinacy Inference for Prolog
This paper revisits the problem of determinacy inference addressing the
problem of how to uniformly handle cut. To this end a new semantics is
introduced for cut, which is abstracted to systematically derive a backward
analysis that derives conditions sufficient for a goal to succeed at most once.
The method is conceptionally simpler and easier to implement than existing
techniques, whilst improving the latter's handling of cut. Formal arguments
substantiate correctness and experimental work, and a tool called 'RedAlert'
demonstrates the method's generality and applicability.Comment: Theory and Practice of Logic Programming, 2011, 27th Int'l.
Conference on Logic Programming (ICLP'11) Special Issue, volume 11, issue 4-
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