Implications of Structured Programming for Machine Architecture

Based on an empirical study of more than 10,000 lines of program text written in a GOTO-less language, a machine architecture specifically designed for structured programs is proposed. Since assignment, CALL, RETURN, and IF statements together account for 93 percent of all executable statements, special care is given to ensure that these statements can be implemented efficiently. A highly compact instruction encoding scheme is presented, which can reduce program size by a factor of 3. Unlike a Huffman code, which utilizes variable length fields, this method uses only fixed length (1-byte) opcode and address fields. The most frequent instructions consist of a single 1-byte field. As a consequence, instruction decoding time is minimized, and the machine is efficient with respect to both space and time. © 1978, ACM. All rights reserved

Topics in Programming Languages, a Philosophical Analysis through the case of Prolog

[EN]Programming languages seldom find proper anchorage in philosophy of logic, language and science. is more, philosophy of language seems to be restricted to natural languages and linguistics, and even philosophy of logic is rarely framed into programming languages topics. The logic programming paradigm and Prolog are, thus, the most adequate paradigm and programming language to work on this subject, combining natural language processing and linguistics, logic programming and constriction methodology on both algorithms and procedures, on an overall philosophizing declarative status. Not only this, but the dimension of the Fifth Generation Computer system related to strong Al wherein Prolog took a major role. and its historical frame in the very crucial dialectic between procedural and declarative paradigms, structuralist and empiricist biases, serves, in exemplar form, to treat straight ahead philosophy of logic, language and science in the contemporaneous age as well. In recounting Prolog's philosophical, mechanical and algorithmic harbingers, the opportunity is open to various routes. We herein shall exemplify some: - the mechanical-computational background explored by Pascal, Leibniz, Boole, Jacquard, Babbage, Konrad Zuse, until reaching to the ACE (Alan Turing) and EDVAC (von Neumann), offering the backbone in computer architecture, and the work of Turing, Church, Gödel, Kleene, von Neumann, Shannon, and others on computability, in parallel lines, throughly studied in detail, permit us to interpret ahead the evolving realm of programming languages. The proper line from lambda-calculus, to the Algol-family, the declarative and procedural split with the C language and Prolog, and the ensuing branching and programming languages explosion and further delimitation, are thereupon inspected as to relate them with the proper syntax, semantics and philosophical élan of logic programming and Prolog

Introduction to the Literature on Semantics

An introduction to the literature on semantics. Included are pointers to the literature on axiomatic semantics, denotational semantics, operational semantics, and type theory

Recursive structure in computer systems

PhD ThesisStructure plays a important part in the design of large systems. Unstructured programs are difficult to design or test and good structure has been recognized as essential to all but the smallest programs. Similarly, concurrently executing computers must co-operate in a structured way if an uncontrolled growth in complexity is to be avoided. The thesis presented here is that recursive structure can be used to organize and simplify large programs and highly parallel computers. In programming, naming concerns the way names are used to identify objects. Various naming schemes are examined including 'block structured' and 'pathname' naming. A new scheme is presented as a synthesis of these two combining most of their advantages. Recursively structured naming is shown to be an advantage when programs are to be de-composed or combined to an arbitrary degree. Also, a contribution to the UNIX United/Newcastle Connection distributed operating system design is described. This shows how recursive naming was used in a practical system. Computation concerns the progress of execution in a computer. A distinction is made between control driven computation where the programmer has explicit control over sequencing and data driven or demand driven computation where sequencing is implicit. It is shown that recursively structured computation has attractive locality properties. The definition of a recursive structure may itself be cyclic (self-referencing). A new resource management ('garbage collection') algorithm is presented which can manage cyclic structures without costs proportional to the system size. The scheme is an extension of 'reference counting'. Finally the need for structure in program and computer design and the advantages of recursive structure are discussed.The Science and Engineering Research Council of Great Britain