An overlaying method for the effective organisation of APL systems
Alison Crossley, G R Streeter · ACM SIGAPL APL Quote Quad · 1979
A system has been developed to manage the workspace with an application operating under its control. The system, known as PROGRAMSYSTEM, utilises a novel overlaying technique to limit workspace contents to those which are pertinent to the current processing task. Having been evolved over the past two years, it is currently managing three large operational applications in different organisations, using Sharp APL and Xerox APL. The paper briefly reviews some popular workspace-management methods using program files, and introduces the concept of Sharp-APL 'packages' on which PROGRAMSYSTEM was based. A characteristic of conventional methods is the use of a directory reference table to locate required objects on the program file. PROGRAMSYSTEM dispenses with this relatively expensive approach. Instead, small functions are generated for the application, which directly reference overlays on a program file; by localising overlay contents within these functions, they are automatically removed from the workspace on termination. The methodology is explained in detail, and demonstrated by example. The structure of the program file is described, including the additional facilities supported by PROGRAMSYSTEM, these being: collection of cost statistics, handling of graphics and terminal characteristics, and extensive automatic documentation capabilities.