V.PROGRAMMING RESEARCH

A.Cedar

Activities

The basic Cedar system has been transferred from the Alto operating environment to Pilot which now runs on both Dolphin and Dorado processors. Several new langauge features, including run-time types, have appeared; and the performance of automatic storage management has been improved. Basic subsystems for interactive programming and system management have been written and are in regular use, though not on Pilot. We have made extensive use of software from SDD and ISL.

Kernel: We have made modifications to the Pilot operating system and related utilities to enable them to execute on the Dorado processor. These involve changes to support a different input/output configuration, most notably, a different kind of rigid disk. There has been extensive work on Dorado and Dolphin microcode to support Pilot and various special input/output devices. [Taft, Levin, Fiala]

Cascade: We have constructed a system called Cascade, which represents the first stage in the transition to a Pilot-based program development environment. Cascade provides the facilities to edit, compile, bind, execute and debug Mesa programs under Pilot without resorting to Alto emulation. To reach this point, we converted the standard SDD Alto/Mesa compiler and binder to run in the CoPilot environment, and built an Executive and other utilities to control the program development cycle. Cascade is presently in use by Cedar implementers as well as the Mesa group in SDD. [Levin, Atkinson, Schmidt]

Language: We have continued to make progress on the conceptual foundations of the Abstract Machine. The aspects of the machine dealing with Mesa values have been implemented and are being used to support the executive and debugging facilities discussed below.

We have improved the compiler, runtime, and Dorado microcode to make incremental collection run faster and semi-concurrently with its clients. We designed modifications that allow the collector to safely and efficiently trace the stacks of processes which deal with collectible storage. A trace-and-sweep garbage collector has been designed and an exploratory implementation has been tested. We wrote a facility for finalization of collectible objects.

New language features were implemented: variable sized arrays, better default initialization, support for dynamic types, LISP-like atoms, and lists. Progress was made on the Cedar/Mesa Primer and Reference manual. An exploratory remote procedure call facility was designed and built. A design for rapid turnaround for minor program changes was completed. An exploratory implementation of an automatic type inference scheme was done. [Rovner, Atkinson, Haugeland, Horning, McKeeman, Satterthwaite, Wells]

User Facilities: Facilities for user terminal input have been written. The client sees an input stream of events such as keystrokes, mouse clicks and chords. The interface also provides a procedure for repositioning the stream as a function of time.

Based on the graphics package provided by ISL, Document classes for file and stream documents have been written. As an exercise, a Document class for displaying LSI layouts was implemented. Scrolling and partial refresh of the screen are operational. A facility for attaching a stream, e.g. the keyboard stream, to a document has been provided.

Based on input streams we wrote a programmable scanner that accepts a sequence of characters from a stream, and returns a dynamically typed Mesa value. An inverse function takes a value delivers a sequence of characters to a stream. Based upon these procedures and Documents, a user executive patterned after Interlisp’s has been written. It accepts inputs of procedure names and argument values, applies the procedure to the arguments, and prints the result. Spelling correction and a REDO facility have been implemented.

Some progress has been made on the design of a comprehensive set of debugging capabilities. A number of special Document types will be used to display understandable representations of the program sources and active data for an instance of an application. Operations available through menus related to these Documents will allow modification of data values and program control state. It will be possible to have one or more independent debugging environments for each simultaneously active application.
[Teitelman, Swinehart, Crowther]

System Models: We wrote programs that will recompile a system of Mesa modules, and will transport consistent versions of systems between machines. These systems operate on an as-needed basis to avoid gratuitous compilaltion and file transfer. We built a database, using the Database package (see elswhere), that contains information about Mesa modules, their dependencies, and their whereabouts on remote file servers. This effort helped discover bugs in the Database package and Juniper.

The design of the system modelling language was refined. A program to convert from the existing descriptions—configuration descriptions and other existing Mesa files—to system models is largely complete. A program that takes these models and determines what needs to be compiled and transferred is partially implemented. [Lampson, Schmidt]

Library: We instituted CedarLib, a facility for user-maintained modules, and distributed many new packages, including a widely-used random number package, IEEE floating point support, a general cache package, support for strings, and initial system modeling software. Software for automatically maintaining CedarLib abstracts and user lists was written. [Atkinson]