A Program Development Environment Based on Persistence and Abstract Data Types

Abstract

This paper describes the design of a program development system used for teaching undergraduate students. The system started life as an experiment with ideas associated with a type domain designed as part of a persistent [1] programming environment [11]. The aim of the experiment was to apply these ideas to the description of facilities usually associated with file-based operating systems, and to find out how well ideas designed to cope with “fine grain” persistent objects, would cope with the kind of “coarse grain” persistent objects usually represented by “files”.

In this paper, objects of type program are defined by an abstract data type supporting the operations, edit, parse, make executable and run. The program development process is controlled through the notion of abstract states which constrain the order of application of the available operations. In addition, the type program may be parametrised by objects of type language.

A more complex type called system is provided. Systems support the same operations as simple programs, but are represented by hierarchies of programs and modules. A set of navigation operations are supported and the abstract state of a system or subsystem is a composition of the abstract states of its components. Users interact with systems as if they were using an interactive, incremental version of the UNIX make command [3].

In addition to the predefined object types described above, the environment supports user defined object types through a mechanism which formalises the concept of a suite of programs, e.g. the new type document might be installed and described by an appropriate set of operations and abstract states.

The system is described in terms of the type domain supported by the Paradox persistent machine [11]. A version of the programming environment has been used by classes of 100 or more students at UMIST since October 1987.