1,721,022 research outputs found
The CakeML Project’s Quest for Ever Stronger Correctness Theorems (Invited Paper)
No full textThe CakeML project has developed a proof-producing code generation mechanism for the HOL4 theorem prover, a verified compiler for ML and, using these, a number of verified application programs that are proved correct down to the machine code that runs them (in some cases, even down to the underlying hardware). The purpose of this extended abstract is to tell the story of the project and to point curious readers to publications where they can read more about specific contributions
Reversible Session-Based Concurrency in Haskell
Full text linkA reversible semantics enables to undo computation steps. Reversing message-passing, concurrent programs is a challenging and delicate task; one typically aims at causally consistent reversible semantics. Prior work has addressed this challenge in the context of a process model of multiparty protocols (or choreographies). In this paper, we describe a Haskell implementation of this reversible operational seman- tics. We exploit algebraic data types to faithfully represent three core ingredients: a process calculus, multiparty session types, and forward and backward reduction semantics. Our implementation bears witness to the convenience of pure functional programming for implementing reversible languages
Colocation of Potential Parallelism in a Distributed Adaptive Run-Time System for Parallel Haskell
No full textThis paper presents a novel variant of work stealing for load balancing in a distributed graph reducer, executing a semi-explicit parallel dialect of Haskell. The key concept of this load-balancer is colocating related sparks (potential parallelism) using maximum prefix matching on the encoding of the spark’s ancestry within the computation tree, reconstructed at run time, in spark selection decisions. We evaluate spark colocation in terms of performance and scalability on a set of five benchmarks on a Beowulf-class cluster of multi-core machines using up to 256 cores. In comparison to the baseline mechanism, we achieve speedup increase of up to 46% for three out of five applications, due to improved locality and load balance throughout the execution as demonstrated by profiling data. For one less scalable program and one program with excessive amounts of very fine-grained parallelism we observe drops in speedup by 17% and 42%, respectively. Overall, spark colocation results in reduced mean time to fetch the required data and in higher degree of parallelism of finer granularity, which is most beneficial on higher PE numbers.</p
High-performance defunctionalisation in futhark
No full textGeneral-purpose massively parallel processors, such as GPUs, have become common, but are difficult to program. Pure functional programming can be a solution, as it guarantees referential transparency, and provides useful combinators for expressing data-parallel computations. Unfortunately, higher-order functions cannot be efficiently implemented on GPUs by the usual means. In this paper, we present a defunctionalisation transformation that relies on type-based restrictions on the use of expressions of functional type, such that we can completely eliminate higher-order functions in all cases, without introducing any branching. We prove the correctness of the transformation and discuss its implementation in Futhark, a data-parallel functional language that generates GPU code. The use of these restricted higher-order functions has no impact on run-time performance, and we argue that we gain many of the benefits of general higher-order functions, without in most practical cases being hindered by the restrictions.</p
A minimalistic verified bootstrapped compiler (proof pearl)
No full text\ua9 2021 ACM. This paper shows how a small verified bootstrapped compiler can be developed inside an interactive theorem prover (ITP). Throughout, emphasis is put on clarity and minimalism
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fast, Verified Computation for Candle
Full text linkThis paper describes how we have added an efficient function for computation to the kernel of the Candle interactive theorem prover. Candle is a CakeML port of HOL Light which we have, in prior work, proved sound w.r.t. the inference rules of the higher-order logic. This paper extends the original implementation and soundness proof with a new kernel function for fast computation. Experiments show that the new computation function is able to speed up certain evaluation proofs by several orders of magnitude
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