Jiapi: A Type Checker Generator for Statically Typed Languages

Type systems are a key characteristic in the context of the study of programming languages. They frequently offer a simple, intuitive way of expressing and testing the fundamental structure of programs. This is especially true when types are used to provide formal, machine-checked documentation for an implementation. For example, the absence of type errors in code prior to execution is what type systems for static programming languages are designed to assure, and in the literature, type systems that satisfy this requirement are referred to as sound type systems. Types also define module interfaces, making them essential for achieving and maintaining consistency in large software systems. On these accounts, type systems can enable early detection of program errors and vastly improve the process of understanding unfamiliar code. However, even for verification professionals, creating mechanized type soundness proofs using the tools and procedures readily available today is a difficult undertaking. Given this result, it is only logical to wonder if we can capture and check more of the program structure, so the next two questions concern type checking. Once a type system has been specified, how can we implement a type checker for the language? Another common question concerns the operational semantics, that is, once the type system is specified, how can we take advantage of this specification to obtain a type checker for the language? In each of these cases, type systems are often too complex to allow for a practical and reasonable approach to specifying many common language features in a natural fashion; therefore, the crux here is: What is the bare minimum set of constructs required to write a type checker specification for any domain-specific language (DSL)? We believe that sets (including tests for memberships, subsets, size, and other properties) as well as first-order logic and an expression grammar can be used to do this. In addition, we will need the ability to apply some form of filter on sets, as well as possibly a reduction and map. The primary goal of this thesis is to raise the degree of automation for type checking, so we present Jiapi, an automatic type checker generation tool. The tool generates a type checker based on a description of a language’s type system expressed in set notation and first-order logic, allowing types to be interpreted as propositions and values to be interpreted as proofs of these propositions, which we can then reduce to a small number of easily-reviewable predicates. Consequently, we can have a completely spelled-out model of a language’s type system that is free of inconsistencies or ambiguities, and we can mathematically demonstrate features of the language and programs written in it. We use two languages as case studies: a somewhat large and more general, and a more domain-specific. The first one is a true subset of Java (an object-oriented language) called Espresso, and the second one is a pedagogical language like C/C++ called C-Minor. Also, there is a declarative type system description extension for the first language, and parts of the specification for the second one. Finally, our approach is evaluated to demonstrate that the generated type checker can check automatically the full functional correctness of an Espresso and C-Minor program

Groupware design : principles, prototypes, and systems

Computers are valuable tools for a wide range of work tasks. A substantial limitation on their value, however, is the predominant focus on enhancing the work of individuals. This fails to account for the issues of collaboration that affect almost all work. Research into computer supported cooperative work (CSCW) aims to eliminate this deficiency, but the promise of computer systems for group work has not been met. This thesis presents four design principles that promote the development of successful groupware. The principles identify the particular problems encountered by groupware, and provide guidelines and strategies to avoid, overcome, or minimise their impact. Derived from several sources, the major influence on the principles development is an investigation into the relationship between factors affecting groupware failure. They are stimulated by observations of groupware use, and by design insights arising from the development of two groupware applications and their prototypes: Mona and TELEFREEK. Mona provides conversation-based email management. Several groupware applications allow similar functionality, but the design principles result in Mona using different mechanisms to achieve its user-support. TELEFREEK provides a platform for accessing computer-supported communication and collaboration facilities. It attends to the problems of initiating interaction, and supports an adaptable and extendible set of "social awareness" assistants. TELEFREEK offers a broader range of facilities than other groupware, and avoids the use of prohibitively high-bandwidth communication networks. TELEFREEK demonstrates that much can be achieved through current and widely accessible technology. Together, Mona and TELEFREEK forcefully demonstrate the use of the design principles, and substantiate the claim of their utility

Universal semantic communication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 325-334).Is meaningful communication possible between two intelligent parties who share no common language or background? We propose that this problem can be rigorously addressed by explicitly focusing on the goals of the communication. We propose a theoretical framework in which we can address when and to what extent such semantic communication is possible. Our starting point is a mathematical definition of a generic goal for communication, that is pursued by agents of bounded computational complexity. We then model a "lack of common language or background" by considering a class of potential partners for communication; in general, this formalism is rich enough to handle varying degrees of common language and backgrounds, but the complete lack of knowledge is modeled by simply considering the class of all partners with which some agent of similar power could achieve our goal. In this formalism, we will find that for many goals (but not all), communication without any common language or background is possible. We call the strategies for achieving goals without relying on such background universal protocols. The main intermediate notions introduced by our theory are formal notions of feedback that we call sensing. We show that sensing captures the essence of whether or not reliable universal protocols can be constructed in many natural settings of interest: we find that across settings, sensing is almost always sufficient, usually necessary, and generally a useful design principle for the construction of universal protocols. We support this last point by developing a number of examples of protocols for specific goals. Notably, we show that universal delegation of computation from a space-efficient client to a general-purpose server is possible, and we show how a variant of TCP can allow end-users on a packet network to automatically adapt to small changes in the packet format (e.g., changes in IP). The latter example above alludes to our main motivation for considering such problems, which is to develop techniques for modeling and constructing computer systems that do not require that their components strictly adhere to protocols: said differently, we hope to be able to design components that function properly with a sufficiently wide range of other components to permit a rich space of "backwards-compatible" designs for those components. We expect that in the long run, this paradigm will lead to simpler systems because "backwards compatibility" is no longer such a severe constraint, and we expect it to lead to more robust systems, partially because the components should be simpler, and partially because such components are inherently robust to deviations from any fixed protocol. Unfortunately, we find that the techniques for communication under the complete absence of any common background suffer from overhead that is too severe for such practical purposes, so we consider two natural approaches for introducing some assumed common background between components while retaining some nontrivial amount of flexibility. The first approach supposes that the designer of a component has some "belief" about what protocols would be "natural" to use to interact with other components; we show that, given sensing and some sufficient "agreement" between the beliefs of the designers of two components, the components can be made universal with some relatively modest overhead. The second approach supposes that the protocols are taken from some restricted class of functions, and we will see that for certain classes of functions and simple goals, efficient universal protocols can again be constructed from sensing. Actually, we show more: the special case of our model described in the second approach above corresponds precisely to the well-known model of mistake-bounded on-line learning first studied by Barzdirs and Frievalds, and later considered in more depth by Littlestone. This connection provides a reasonably complete picture of the conditions under which we can apply the second approach. Furthermore, it also seems that the first approach is closely related to the problem of designing good user interfaces in Human-Computer Interaction. We conclude by briefly sketching the connection, and suggest that further development of this connection may be a potentially fruitful direction for future work.by Brendan Juba.Ph.D

Maritime expressions:a corpus based exploration of maritime metaphors

This study uses a purpose-built corpus to explore the linguistic legacy of Britain’s maritime history found in the form of hundreds of specialised ‘Maritime Expressions’ (MEs), such as TAKEN ABACK, ANCHOR and ALOOF, that permeate modern English. Selecting just those expressions commencing with ’A’, it analyses 61 MEs in detail and describes the processes by which these technical expressions, from a highly specialised occupational discourse community, have made their way into modern English. The Maritime Text Corpus (MTC) comprises 8.8 million words, encompassing a range of text types and registers, selected to provide a cross-section of ‘maritime’ writing. It is analysed using WordSmith analytical software (Scott, 2010), with the 100 million-word British National Corpus (BNC) as a reference corpus. Using the MTC, a list of keywords of specific salience within the maritime discourse has been compiled and, using frequency data, concordances and collocations, these MEs are described in detail and their use and form in the MTC and the BNC is compared. The study examines the transformation from ME to figurative use in the general discourse, in terms of form and metaphoricity. MEs are classified according to their metaphorical strength and their transference from maritime usage into new registers and domains such as those of business, politics, sports and reportage etc. A revised model of metaphoricity is developed and a new category of figurative expression, the ‘resonator’, is proposed. Additionally, developing the work of Lakov and Johnson, Kovesces and others on Conceptual Metaphor Theory (CMT), a number of Maritime Conceptual Metaphors are identified and their cultural significance is discussed

Massachusetts Domestic and Foreign Corporations Subject to an Excise: For the Use of Assessors (2004)

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