Normalization by evaluation for call-by-push-value and polarized lambda calculus

We observe that normalization by evaluation for simply-typed lambda-calculus with weak coproducts can be carried out in a weak bi-cartesian closed category of presheaves equipped with a monad that allows us to perform case distinction on neutral terms of sum type. The placement of the monad influences the normal forms we obtain: for instance, placing the monad on coproducts gives us eta-long beta-pi normal forms where pi refers to permutation of case distinctions out of elimination positions. We further observe that placing the monad on every coproduct is rather wasteful, and an optimal placement of the monad can be determined by considering polarized simple types inspired by focalization. Polarization classifies types into positive and negative, and it is sufficient to place the monad at the embedding of positive types into negative ones. We consider two calculi based on polarized types: pure call-by-push-value (CBPV) and polarized lambda-calculus, the natural deduction calculus corresponding to focalized sequent calculus. For these two calculi, we present algorithms for normalization by evaluation. We further discuss different implementations of the monad and their relation to existing normalization proofs for lambda-calculus with sums. Our developments have been partially formalized in the Agda proof assistant

Classical logic, continuation semantics and abstract machines

One of the goals of this paper is to demonstrate that denotational semantics is useful for operational issues like implementation of functional languages by abstract machines. This is exemplified in a tutorial way by studying the case of extensional untyped call-by-name λ-calculus with Felleisen's control operator 𝒞. We derive the transition rules for an abstract machine from a continuation semantics which appears as a generalization of the ¬¬-translation known from logic. The resulting abstract machine appears as an extension of Krivine's machine implementing head reduction. Though the result, namely Krivine's machine, is well known our method of deriving it from continuation semantics is new and applicable to other languages (as e.g. call-by-value variants). Further new results are that Scott's D∞-models are all instances of continuation models. Moreover, we extend our continuation semantics to Parigot's λμ-calculus from which we derive an extension of Krivine's machine for λμ-calculus. The relation between continuation semantics and the abstract machines is made precise by proving computational adequacy results employing an elegant method introduced by Pitts

Automatic Identification of Structural Process Weaknesses – Experiences with Semantic Business Process Modeling in the Financial Sector

Business process reengineering (BPR) has been a core research topic for at least the last twenty years. As banks have realized the need to look on their business in a process-oriented way, they have been engaged in numerous business process reengineering projects to make their organizations more efficient. However, the success of BPR projects in banks varies significantly and it remains a challenge to systematically discover weaknesses in business process landscapes. Based on the Semantic Business Process Modeling Language (SBPML) this paper introduces a new approach for pattern-based automatic process model analysis, with a focus on identifying structural process weaknesses such as organizational process fragmentation, possibly unnecessary process complexity or multiple resource usage or other process inefficiencies. Additionally, this approach also allows for a benchmarking of different process path alternatives in the same process or among different processes. In this article, this approach is applied and evaluated in the financial sector, but it can possibly also be used in other domains. It contributes to a more efficient and more effective identification of possible weaknesses in process models in comparison to today’s manual analysis of process models

The Political Economy of fin-de-siecle Christian Socialism.

The term 'Christian Socialism' carries two meanings: firstly, it denotes an abstract political and theological idea; and secondly, it refers to the various figures and organizations who laid claim to the term throughout history, and who fought for social justice under its banner. It is the latter definition given above that describes the theoretical scope of this thesis, but on the basis of the research some tentative thoughts are offered on Christian Socialism as a political philosophy. Few works of scholarly literature have sought to critically analyse the history of the movement without also explicitly or implicitly advancing particular notions of what the 'essence' of Christian Socialism was, and what it ought to be. This thesis aims to address this historiographical imbalance by investigating the social, political, and economic ideas of the fin-de-siecle Christian Socialists in light of their historical context. To do so, the thesis conceives of Christian Socialist political economy not in terms of its leaders' theories, but as it was expounded by the movement's leading theorists as they engaged with contemporary socialist and economic discourse. These theorists were the editors and authors of the movement's political literature, which comprised numerous sermons, pamphlets, novels, textbooks, and magazines, as well as periodicals such as The Economic Review. These sources have been used to trace the Christian Socialists' attempts to challenge popular conceptions of the poor, of socialism, and of political economy, as well as their attempts to forge a Christian economics based on their understanding of contemporary strands of economic and socialist thought. The thesis uncovers several previously marginalized aspects of the history of Victorian and Edwardian Christian Socialism, such as: the movement's interaction with and use of the ideas of J. A. Hobson, Alfred Marshall, Karl Marx, and the historical school of economics; the movement's popularization of economic theory and secular socialist doctrines; and the movement's promulgation of collectivist economic socialism throughout the late nineteenth century and early twentieth century

Practical Normalization by Evaluation for EDSLs

Embedded domain-specific languages (eDSLs) are typically implemented in a rich host language, such as Haskell, using a combination of deep and shallow embedding techniques. While such a combination enables programmers to exploit the execution mechanism of Haskell to build and specialize eDSL programs, it blurs the distinction between the host language and the eDSL. As a consequence, extension with features such as sums and effects requires a significant amount of ingenuity from the eDSL designer. In this paper, we demonstrate that Normalization by Evaluation (NbE) provides a principled framework for building, extending, and customizing eDSLs. We present a comprehensive treatment of NbE for deeply embedded eDSLs in Haskell that involves a rich set of features such as sums, arrays, exceptions and state, while addressing practical concerns about normalization such as code expansion and the addition of domain-specific features

POPLMark reloaded: Mechanizing proofs by logical relations

We propose a new collection of benchmark problems in mechanizing the metatheory of programming languages, in order to compare and push the state of the art of proof assistants. In particular, we focus on proofs using logical relations (LRs) and propose establishing strong normalization of a simply typed calculus with a proof by Kripke-style LRs as a benchmark. We give a modern view of this well-understood problem by formulating our LR on well-typed terms. Using this case study, we share some of the lessons learned tackling this problem in different dependently typed proof environments. In particular, we consider the mechanization in Beluga, a proof environment that supports higher-order abstract syntax encodings and contrast it to the development and strategies used in general-purpose proof assistants such as Coq and Agda. The goal of this paper is to engage the community in discussions on what support in proof environments is needed to truly bring mechanized metatheory to the masses and engage said community in the crafting of future benchmarks

Learner support services in full-service schools: voices of parents in Uthukela district Kwazulu-Natal

Master Degree.University of KwaZulu-Natal, Durban.Support is regarded as the cornerstone of Full-service schools. The government of South Africa introduced full-service school in order to channel inclusive education. For support to be fully embedded in the full-service school all stakeholders should take their rightful positions and that includes parents. Voices of parents are very limited within South African ambience and it is for this reason that this study’s focus is on what the parents say. This study was conducted to explore learner support services in full-service schools: voices of parents in uThukela district, KwaZulu-Natal. A literature study of international, national and local was done in order to understand the concept not just at our point of departure level but rather nationally. This was the phenomenological study which focused on Thlapeng¹ and Letlokwa¹ full-service schools that are based at KwaZulu-Natal’s uThukela district. A qualitative approach with purposeful sampling was used within an interpretive paradigm. The triangulation of data and theories was done using semi-structured interviews and questionnaires as well as Asset-based theory and Epstein’s theory of overlapping spheres. The three themes that emerged during analysis were; Theme one: Parents understanding of full-service school, theme two: learner support services in full-service schools is kaleidoscopic and theme three: discourses of support. The findings from these themes suggest that parents find the support in these school as kaleidoscopic and it also clear even though parents are the third leg of the three legged pot that forms the basis of proper functionality at these schools are not fully involved in the processes with regards to the support of learners in these schools. Their involvement is very limited or restricted which is in contradiction with what the policy on Full-service schools and SIAS document require

Powder Characterisation, Microstructure, and Mechanical Property Evolution of IN625 and IN718 During Selective Laser Melting and Heat Treatment

Additive layer manufacturing is a blanket term for a wide range of processes operating on the same underlying principle. 3D geometry is created by depositing material, layer by layer to create a final 3D geometry. Selective laser melting (SLM) is a branch of additive layer manufacturing, using a laser to fuse a powder bed of metal into each layer. This thesis investigates the SLM process and its application to nickel based superalloy materials, IN625 and IN718. IN625 and IN718 are similar nickel-based superalloys developed for use in aerospace gas turbine engines. In their conventionally manufactured form, these materials have excellent high temperature mechanical properties which make them idea for use in the hot section of gas turbine engines. The aim of this thesis was to investigate how these materials interact with the SLM process and how the material produced can be optimised to improve the range of applications it can be used for. A gap in knowledge regarding a detailed understanding of how the powders morphological and rheological properties influence its ability to be processed by SLM was identified and investigated. A wide range of characterisation methods were implemented with certain important properties being identified to assess a powders processability, namely the particle size distribution and how a significant content of fine particles below 10 μm in size can be detrimental to processability. There is also a lack of a standard powder characterisation methodology specifically for SLM applications. This is addressed with certain methods and measurements being suggested as most promising for wider SLM application. Avalanche flow testing is found to be most applicable to the critical recoating process in SLM and most able to differentiate suitable and unsuitable SLM powders. Following characterisation of the raw material feedstock powder, this thesis also investigates the influence of processing parameters on the microstructure of the material produced by the SLM process. Significant microstructural changes were observed as a result of process parameter changes. This was identified to potentially enable for in-situ modification of material microstructure to suit a manufactured material to its end application. Of the process parameters investigated, laser scan speed was most interesting, suggesting that a faster laser scan speed was able to create a similar microstructure to a much slower one. This was attributed to the reheating effect of the laser beam returning quickly to the adjacent scan line. The validity of this explanation was investigated using a simple, computational thermal model. The result is a new understanding of laser scan speed SLM and its nonlinear relationship with material temperature and microstructure evolution. Finally, post process heat treatments of SLM manufactured IN718 material were investigated. This investigation was in response to a gap in current knowledge regarding heat treatments designed specifically for SLM material. SLM IN718 has been found to have reduced high temperature mechanical properties, specifically stress rupture, which limits its application in demanding environments. In this thesis a range of post process homogenisation heat treatments were investigated, with treatments between 1030 °C and 1060 °C being found to produce material with characteristics consistent with material with excellent stress rupture properties. This novel heat treatment route could provide a method for SLM IM718, and the increased design and geometric freedoms, to be applied in more demanding applications. An evolution of the grain structure in the material was also observed and measured during high temperature homogenisation treatments. This was investigated in the final chapter, and a novel mechanism is suggested for the process of grain coarsening observed. Previously published literature explains similar evolutions as recrystallisation however this did not fit the observations during this thesis. The evolution of grain structure was observed using a process of quasi in-situ electron back scatter diffraction, and a mechanism of grain boundary length reduction, followed by grain growth, is suggested to better fit the observations. It was determined that grains are preferentially selected for growth based on their proximity to a ‘path of least resistance’ of lower angle grain boundaries. The results of this work should benefit industrial users of SLM in the fabrication of Nickel-Based Superalloy material for aerospace applications. The conclusions on powder characterisation offer an insight into available methods to better control and characterise powder feedstock materials for consistent production. Aerospace users especially may find the work regarding post process heat treatments designed specifically for SLM material, to recover lost stress rupture performance, useful in enabling the use of SLM materials, and the design freedom that brings with it, in mor demanding environments than are currently possible

THE FERRY SERVICE OFFER AN ANALYSIS OF FERRY SERVICES OPERATING FROM AND WITHIN THE UNITED KINGDOM

The objective of this study is to investigate the market offer of passenger-car ferry services within and from the United Kingdom. The study is approached from the pomt of view of the provider of the ferry service offer. Initially, it seeks to analyse the existing ferry services offered within and from the United Kingdom by the various operators, and subsequently undertakes an empirical investigation based on the appropriate marketing and management theory. The role of the consumer is, of course, crucial to an understanding of the marketing of ferry services. However, this particular study focuses on the supply of the ferry offer, and may be seen as complementary to earUer studies of ferry consumers and benefits sought. A comparison of on-board facilities and services on 70 ferries operating in the UK in 1994 resulted in the development of a basehne model explaining differences between services according to a wide range of criteria. This led to the development of a conceptual model of the ferry service offer using concepts from services marketing and corporate culture theory. Using cluster analysis it was concluded that the ferry service offer can be described in terms of core, augmented, and inter-product levels. In addition to these three ferry service offer levels the preferred service provider of each particular ferry service element has been identified. Using multiple discriminant analysis it was concluded that the augmented ferry service offer can be explained by differences among Miles & Snow corporate culture types (prospectors, analysers, and defenders). Combining these results, this study provides an explanation of the ferry service offer in terms of product level, preferred provider, and dominant corporate culture, which should prove of both practical and theoretical value