The productivity of polymorphic stream equations and the composition of circular traversals

This thesis has two independent parts concerned with different aspects of laziness in functional programs. The first part is a theoretical study of productivity for very restricted stream programs. In the second part we define a programming abstraction over a recursive pattern for defining circular traversals modularly. Productivity is in general undecidable. By restricting ourselves to mutually recursive polymorphic stream equations having only three basic operations, namely "head", "tail", and "cons", we aim to prove interesting properties about productivity. Still undecidable for this restricted class of programs, productivity of polymorphic stream functions is equivalent to the totality of their indexing function, which characterise their behaviour in terms of operations on indices. We prove that our equations generate all possible polymorphic stream functions, and therefore their indexing functions are all the computable functions, whose totality problem is indeed undecidable. We then further restrict our language by reducing the numbers of equations and parameters, but despite those constraints the equations retain their expressiveness. In the end we establish that even two non-mutually recursive equations on unary stream functions are undecidable with complexity $Π_2^0$. However, the productivity of a single unary equation is decidable. Circular traversals have been used in the eighties as an optimisation to combine multiple traversals in a single traversal. In particular they provide more opportunities for applying deforestation techniques since it is the case that an intermediate datastructure can only be eliminated if it is consumed only once. Another use of circular programs is in the implementation of attribute grammars in lazy functional languages. There is a systematic transformation to define a circular traversal equivalent to multiple traversals. Programming with this technique is not modular since the individual traversals are merged together. Some tools exist to transform programs automatically and attribute grammars have been suggested as a way to describe the circular traversals modularly. Going to the root of the problem, we identify a recursive pattern that allows us to define circular programs modularly in a functional style. We give two successive implementations, the first one is based on algebras and has limited scope: not all circular traversals can be defined this way. We show that the recursive scheme underlying attribute grammars computation rules is essential to combine circular programs. We implement a generic recursive operation on a novel attribute grammar abstraction, using containers as a parametric generic representation of recursive datatypes. The abstraction makes attribute grammars first-class objects. Such a strongly typed implementation is novel and make it possible to implement a high level embedded language for defining attribute grammars, with many interesting new features promoting modularity

The productivity of polymorphic stream equations and the composition of circular traversals

This thesis has two independent parts concerned with different aspects of laziness in functional programs. The first part is a theoretical study of productivity for very restricted stream programs. In the second part we define a programming abstraction over a recursive pattern for defining circular traversals modularly. Productivity is in general undecidable. By restricting ourselves to mutually recursive polymorphic stream equations having only three basic operations, namely "head", "tail", and "cons", we aim to prove interesting properties about productivity. Still undecidable for this restricted class of programs, productivity of polymorphic stream functions is equivalent to the totality of their indexing function, which characterise their behaviour in terms of operations on indices. We prove that our equations generate all possible polymorphic stream functions, and therefore their indexing functions are all the computable functions, whose totality problem is indeed undecidable. We then further restrict our language by reducing the numbers of equations and parameters, but despite those constraints the equations retain their expressiveness. In the end we establish that even two non-mutually recursive equations on unary stream functions are undecidable with complexity $Π_2^0$. However, the productivity of a single unary equation is decidable. Circular traversals have been used in the eighties as an optimisation to combine multiple traversals in a single traversal. In particular they provide more opportunities for applying deforestation techniques since it is the case that an intermediate datastructure can only be eliminated if it is consumed only once. Another use of circular programs is in the implementation of attribute grammars in lazy functional languages. There is a systematic transformation to define a circular traversal equivalent to multiple traversals. Programming with this technique is not modular since the individual traversals are merged together. Some tools exist to transform programs automatically and attribute grammars have been suggested as a way to describe the circular traversals modularly. Going to the root of the problem, we identify a recursive pattern that allows us to define circular programs modularly in a functional style. We give two successive implementations, the first one is based on algebras and has limited scope: not all circular traversals can be defined this way. We show that the recursive scheme underlying attribute grammars computation rules is essential to combine circular programs. We implement a generic recursive operation on a novel attribute grammar abstraction, using containers as a parametric generic representation of recursive datatypes. The abstraction makes attribute grammars first-class objects. Such a strongly typed implementation is novel and make it possible to implement a high level embedded language for defining attribute grammars, with many interesting new features promoting modularity

An Anthropology of Well-Being: Local Perspectives and Cultural Constructions in the Bolivian Altiplano

This thesis focuses on individual and collective definitions of 'the good life' in the Bolivian plateau. Drawing on ethnographic research conducted in the urban area of EI Alto, the thesis explores potential contradictions between different orientations and models of well-being. The increasing interest amongst a group of Aymara intellectuals (GTZ) in an indigenous perspective on this topic provides the point of departure for an exploration of the complexity of ideas relating to this issue and an account of different definitions of 'the good life' among Aymara people. The thesis makes a contribution to debates regarding poverty and well-being and the problems attached to universal definitions, which tend to be based on simplified and economic criteria. By considering what different people value and prioritise in terms of their own well-being and, where applicable, their children's well-being and happiness, the thesis offers a contribution to Andean anthropology and to the understanding of 'poverty'. This entails an exploration of the moments of tension and synergy that exist between Aymara and Bolivian identity. It offers a detailed analysis of different collective and individual actions adopted for the achievement of well-being. In particular, these include social protests, moments of fiesta, household cooperation, and the resort to supernatural forces and 'making of luck (suerte), with a specific focus on gender and generational differences

Threads of virtue : the ethical lives of Syrian textile traders

This thesis is an ethnographic study of ethical concepts and practices among contemporary Muslim textile traders and entrepreneurs in Aleppo, Syria. It draws on Lambek's perspective that ethics is 'ordinary': an inherent and pervasive aspect of exchange transactions, such as visits, hospitality, retail transactions and the negotiations leading up to them. Three ethnographic settings are explored - a textile factory in the north of Aleppo; a wholesale yarn market in the centre of Aleppo's old city markets that is also the site for speculative futures-trading; and a retail fabric shop where young salesmen are employed to get the best price they can from their mainly female customers. The moral processes, concepts and accomplishments that emerge in these different settings include affection and generosity; intention and pure-heartedness; substance and trustworthiness; autonomy, dignity and worth; and obligation and moral reasoning. The thesis describes the different ways that exchanges mediate these processes. This thesis approaches ethics as a function of life lived with others: an aspect of how one should be involved with others, and how one should manage, limit, extend and orient oneself in that involvement. One theme that emerges is how the relationship between autonomy and generosity is managed in these settings, by actors with differential access to resources. Another is what 'sincerity' means: is virtue simply a question of mastering the protocols that govern these exchanges, or is it a matter of the heart? How can social actors tell the difference? Why and when does it matter to them to be able to do so? This thesis also explores the connections between power relationships and ethical practice, arguing that ethics can never be isolated from power, but nor can it be collapsed into it. Moral accomplishments such as generosity, sincerity or affection can be ways of making and organising claims to social status and capital, and of course depend on these things too. However, they also define types of sociality – such as 'intimacy' and 'continuity' - that are seen as having intrinsic worth

From Centre to Margin: Memory, Mobility and Social Change in a Bolivian Town

This thesis addresses social change in Tapacarí, a small rural town in Cochabamba, Bolivia. Tapacarí, which was once an important colonial town and home to an elite controlling the peasant population around it, is now largely empty due to high levels of migration to urban centres. The town retains symbolic and ritual importance for indigenous peasant people and former townspeople in different ways, but becomes more economically marginalised as the economic and kin relationships between these groups changes. The thesis proposes that the town now be seen as one point on a wider array of multiple residences used by indigenous and peasant people as they respond flexibly to unpredictable economic conditions and build autonomy. At the same time the town exists as a place of memory and history for the people who no longer live there, and who come once a year for the fiesta. Based on long-term multi-sited ethnographic fieldwork, the thesis locates small-scale processes of cultural production, discrimination and resistance within larger national and international political and cultural narratives. Through examination of spatial divisions, ritual and local government bureaucracy, a depiction of the fractures and tensions of small town life emerges. It engages with the elasticity of ‘the local’ and the different ways of belonging to a place where few people now live, in the context of a wider conversation about indigeneity, identity and memory arising from political and social change in Bolivia in the early years of the 21st century, including the election of Evo Morales. Through discussion of religious and civic events as well as everyday life, this research shows that those who belong to the town form intimate and contradictory relationships which both fracture along and cross over barriers of class, location and ethnicity

African Studies Abstracts Online: number 18, 2007

ASA Online provides a quarterly overview of journal articles and edited works on Africa in the field of the social sciences and the humanities available in the ASC library. Issue 18 (2007). African Studies Centre, Leiden.ASC – Publicaties niet-programma gebonde