From the type of a polymorphic function we can derive a theorem that it satisfies. Every function of the same type satisfies the same theorem. This provides a free source of useful theorems, courtesy of Reynolds' abstraction theorem for the polymorphic lambda calculus.

Several related typed languages for modular programming and data abstraction have been proposed recently, including Pebble, SOL, and ML modules. We review and compare the basic type-theoretic ideas behind these languages and evaluate how they

Abstract not found

Denotational semantics is given for a Java-like language with pointers, subclassing and dynamic dispatch, class oriented visibility control, recursive types and methods, and privilegebased access control. Representation independence (relational parametricity) is proved, using a semantic notion of confinement similar to ones for which static disciplines have been recently proposed.

In computer science we speak of implementing a logic; this is done in a programming language, such as Lisp, called here the implementation language. We also reason about the logic, as in understanding how to search for proofs; these arguments are expressed in the metalanguage and conducted in the metalogic of the object language being implemented. We also reason about the implementation itself, say to know it is correct; this is done in a programming logic. How do all these logics relate? This paper considers that question and more. We show that by taking the view that the metalogic is primary, these other parts are related in standard ways. The metalogic should be suitably rich so that the object logic can be presented as an abstract data type, and it must be suitably computational (or constructive) so that an instance of that type is an implementation. The data type abstractly encodes all that is relevant for metareasoning, i.e., not only the term constructing functions but also the...

Mitchell’s notion of representation independence is a particularly useful application of Reynolds ’ relational parametricity — two different implementations of an abstract data type can be shown contextually equivalent so long as there exists a relation between their type representations that is preserved by their operations. There have been a number of methods proposed for proving representation independence in various pure extensions of System F (where data abstraction is achieved through existential typing), as well as in Algol- or Java-like languages (where data abstraction is achieved through the use of local mutable state). However, none of these approaches addresses the interaction of existential type abstraction and local state. In particular, none allows one to prove representation independence results for generative ADTs — i.e., ADTs that both maintain some local state and define abstract types whose internal

Abstract not found

The Fox project will use an advanced programming language to build software such as operating systems, network protocols, and distributed systems. The goals of the project are to improve the design and construction of real systems software and to further the development of advanced programming languages. We will base our work on Standard ML, a modern functional programming language that provides polymorphism, first-class functions, exception handling, garbage collection, a parameterized module system, static typing, and formal semantics. The Fox project spans a wide range of research interests, from experimental systems building to type theory, and involves several faculty members. This research was sponsored by the Air Force Systems Command and the Defense Advanced Research Projects Agency (DARPA) under Contract F19628-91-C-0128. The views and conclusionscontained in this document are those of the authors and should not be interpreted as representing the official policies, either expr...

Abstract. A properly encapsulated data representation can be revised for refactoring or other purposes without affecting the correctness of client programs and extensions of a class. But encapsulation is difficult to achieve in object-oriented programs owing to heap based structures and reentrant callbacks. This paper shows that it is achieved by a discipline using assertions and auxiliary fields to manage invariants and transferrable ownership. The main result is representation independence: a rule for modular proof of equivalence of class implementations. 1

An overview of past, present and future work on the Extended ML formal program development framework is given, with emphasis on two topics of current active research: the semantics of the Extended ML specification language, and tools to support formal program development.