. Any multiprocessing facility must include three features: elementary exclusion, data protection, and process saving. While elementary exclusion must rest on some hardware facility (e.g., a test-and-set instruction), the other two requirements are fulfilled by features already present in applicative languages. Data protection may be obtained through the use of procedures (closures or funargs), and process saving may be obtained through the use of the catch operator. The use of catch, in particular, allows an elegant treatment of process saving. We demonstrate these techniques by writing the kernel and some modules for a multiprocessing system. The kernel is very small. Many functions which one would normally expect to find inside the kernel are completely decentralized. We consider the implementation of other schedulers, interrupts, and the implications of these ideas for language design. 1. Introduction In the past few years, researchers have made progress in understanding the mecha...

The very success and breadth of reflective techniques underscores the need for a general theory of reflection. At present what we have is a wide-ranging variety of reflective systems, each explained in its own idiosyncratic terms. Metalogical foundations can allow us to capture the essential aspects of reflective systems in a formalismindependent way. This paper proposes metalogical axioms for reflective logics and declarative languages based on the theory of general logics [34]. In this way, several strands of work in reflection, including functional, equational, Horn logic, and rewriting logic reflective languages, as well as a variety of reflective theorem proving systems are placed within a common theoretical framework. General axioms for computational strategies, and for the internalization of those strategies in a reflective logic are also given. 1 Introduction Reflection is a fundamental idea. In logic it has been vigorously pursued by many researchers since the fundamental wor...

We describe a programming language called Symmetric Lisp that treats environments as first­class objects. Symmetric Lisp allows programmers to write expressions that evaluate to environments, and to create and denote variables and constants of type environment as well. One consequence is that the roles filled in other languages by a variety of limited, special purpose environment forms like records, structures, closures, modules, classes and abstract data types are filled instead by a single versatile and powerful structure. In addition to being its fundamental structuring tool, environments also serve as the basic functional object in the language. Because the elements of an environment are evaluated in parallel, Symmetric Lisp is a parallel programming language; because they may be assembled dyamically as well as statically, Symmetric Lisp accomodates an unusually flexible and simple (parallel) interpreter as well as other history­sensitive applications requiring dynamic environments. We show that first­class environments bring about fundamental changes in a language's structure: conventional distinctions between declarations and expressions, data structures and program structures, passive modules and active processes disappear. We argue that the resulting language is clean, simple and powerful.

Namespace management is fundamental (in a practical sense) to the design of any programming language: how are naming environments built, and how are they used? Modern programming languages come equipped with a variety of mechanisms to create and manipulate naming environments. These mechanisms fall into two broad categories: program structures and data structures. Program structures and data structures are treated differently in modern programming languages. Program structures are not considered to be data structures: they cannot be examined, nor can they be used as components of other data structures. Nor are data structures considered to be programs: they do not specify a scope, nor can they contain expressions as primitive components. This thesis presents a new programming model called the symmetric model in which the representation of programs is identical to the representation of data: to specify a computation, one defines a data structure. This data structure possesses the seman...

this paper I briefly sketch recent work on meta-logical foundations that seems promising as a conceptual basis on which to achieve the goal of formal interoperability. Specificaly, I will briefly discuss:

this paper applications of reflection in rewriting logic and Maude to the following areas:

The goal of achieving powerful problem solving capabilities leads to the "advice taker" form of program and the associated problem of control. This proposal outlines an approach to this problem based on the construction of problem solvers with advanced self-knowledge and introspection capabilities. 1 The Problem of Control Self-reverence, self-knowledge, self-control, These three alone lead life to sovereign power. Alfred, Lord Tennyson, OEnone Know prudent cautious self-control is wisdom's root. Robert Burns, A Bard's Epitath The woman that deliberates is lost. Joseph Addison, Cato A major goal of Artificial Intelligence is to construct an "advice taker", 1 a program which can be told new knowledge and advised about how that knowledge may be useful. Many of the approaches towards this goal have proposed constructing additive formalisms for transmitting knowledge to the problem solver. 2 In spite of considerable work along these lines, formalisms for advising problem solvers ab...

1.1 What is a compiler?....................... 1 1.2 The phases of a compiler.................... 2 1.3 Interpreters........................... 3