2,650 research outputs found
Singular and Plural Functions for Functional Logic Programming
Functional logic programming (FLP) languages use non-terminating and
non-confluent constructor systems (CS's) as programs in order to define
non-strict non-determi-nistic functions. Two semantic alternatives have been
usually considered for parameter passing with this kind of functions: call-time
choice and run-time choice. While the former is the standard choice of modern
FLP languages, the latter lacks some properties---mainly
compositionality---that have prevented its use in practical FLP systems.
Traditionally it has been considered that call-time choice induces a singular
denotational semantics, while run-time choice induces a plural semantics. We
have discovered that this latter identification is wrong when pattern matching
is involved, and thus we propose two novel compositional plural semantics for
CS's that are different from run-time choice.
We study the basic properties of our plural semantics---compositionality,
polarity, monotonicity for substitutions, and a restricted form of the bubbling
property for constructor systems---and the relation between them and to
previous proposals, concluding that these semantics form a hierarchy in the
sense of set inclusion of the set of computed values. We have also identified a
class of programs characterized by a syntactic criterion for which the proposed
plural semantics behave the same, and a program transformation that can be used
to simulate one of them by term rewriting. At the practical level, we study how
to use the expressive capabilities of these semantics for improving the
declarative flavour of programs. We also propose a language which combines
call-time choice and our plural semantics, that we have implemented in Maude.
The resulting interpreter is employed to test several significant examples
showing the capabilities of the combined semantics.
To appear in Theory and Practice of Logic Programming (TPLP)Comment: 53 pages, 5 figure
Reasoning and Improving on Software Resilience against Unanticipated Exceptions
In software, there are the errors anticipated at specification and design
time, those encountered at development and testing time, and those that happen
in production mode yet never anticipated. In this paper, we aim at reasoning on
the ability of software to correctly handle unanticipated exceptions. We
propose an algorithm, called short-circuit testing, which injects exceptions
during test suite execution so as to simulate unanticipated errors. This
algorithm collects data that is used as input for verifying two formal
exception contracts that capture two resilience properties. Our evaluation on 9
test suites, with 78% line coverage in average, analyzes 241 executed catch
blocks, shows that 101 of them expose resilience properties and that 84 can be
transformed to be more resilient
On the Correctness of Pull-Tabbing
Pull-tabbing is an evaluation approach for functional logic computations,
based on a graph transformation recently proposed, which avoids making
irrevocable non-deterministic choices that would jeopardize the completeness of
computations. In contrast to other approaches with this property, it does not
require an upfront cloning of a possibly large portion of the choice's context.
We formally define the pull-tab transformation, characterize the class of
programs for which the transformation is intended, extend the computations in
these programs to include the transformation, and prove the correctness of the
extended computations
Higher derivative terms including the Ramond-Ramond five-form
Superfield methods can be used to determine the precise way the self-dual
five-form couples to the metric in the first non-trivial corrections
to type IIB supergravity. We explicitly compute the exact tensor structure of
these terms. This requires extensive use of computing algorithms to reduce the
complicated expressions that appear to a surprisingly simple form. Along the
way we show a new method of computing Schouten identities. With this result we
clarify under which conditions one may neglect the five-form higher derivative
terms. We comment on corrections to the thermodynamics of charged black holes.Comment: v2 - Numerical typos fixed, small text changes
The influence of particle residence time distribution on the reactivity in fluidized bed reactors
The influence of particle residence time distribution on the average conversion rate (or reactivity) of particles undergoing a non-catalytic gas-solid reaction inside a continuously operated fluidized bed reactor is evaluated. A so called ß-factor is defined as the ratio of the actual reactivity in the reactor and the reactivity of a batch of particles that react under similar circumstances and that all have a conversion extent equal to the average conversion extent in the reactor. The ß-factor concept is elaborated for shrinking core conversion behaviour. According to Heesink et al. (1993), three extreme types of conversion behaviour are distinguished: core reaction limitation, product-layer diffusion limitation and grain reaction limitation. For each type of behaviour a mathematical function is derived that expresses ß as function of average particle conversion, maximum attainable conversion (with regard to pore plugging) and a new-defined expansion factor, which is a measure for the expansion (or shrinking) of the reacting solid during conversion. These functions can be easily incorporated in fluidized bed reactor models
The acquaintance inference with 'seem'-reports
Some assertions give rise to the acquaintance inference: the inference that the speaker is acquainted with some individual. Discussion of the acquaintance inference has previously focused on assertions about aesthetic matters and personal tastes (e.g. 'The cake is tasty'), but it also arises with reports about how things seem (e.g. 'Tom seems like he's cooking'). 'Seem'-reports give rise to puzzling acquaintance behavior, with no analogue in the previously-discussed domains. In particular, these reports call for a distinction between the specific acquaintance inference (that the speaker is acquainted with a specific individual) and the general acquaintance inference (that the speaker is acquainted with something or other of relevance). We frame a novel empirical generalization -- the specific with stage-level generalization -- that systematizes the observed behavior, in terms of the semantics of the embedded 'like'-clause. We present supporting experimental work, and explain why the generalization makes sense given the evidential role of 'seem'-reports. Finally, we discuss the relevance of this result for extant proposals about the semantics of 'seem'-reports. More modestly, it fills a gap in previous theories by identifying which reports get which of two possible interpretations; more radically, it suggests a revision of the kind of explanation that should be given for the acquaintance behavior in question
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