The Waterloo Pascal Compiler

Software Description

The Waterloo Pascal compiler is a debugging-oriented, "load-and-go" compiler designed for use in multi-user timesharing environments. It features a complete implementation of ANSI/IEEE 777X3.97-1983 standard Pascal, as well as several extensions to the language.

Design Goals

Since Waterloo Pascal is primarily a "debugging" compiler, it is most applicable in environments where undebugged programs are to be turned into working programs. Such a compiler has a particular set of design objectives:

• a fast compilation rate;
• a comprehensive set of readily-understandable compile-time diagnostics in full English text (as opposed to error codes or numbers);
• a run-time environment that ensures that all run-time violations are detected and meaningfully diagnosed; and
• facilities which enable the user to debug programs quickly and efficiently.

Waterloo Pascal is equally useful as a teaching tool in classroom situations, or as a "checkout" compiler in industry.

Features

• The language accepted by Waterloo Pascal is the full ANSI standard Pascal (which is equivalent to ISO Level 0 Pascal), plus the extensions noted below.
• An integral part of Waterloo Pascal is an interactive debugger which may be used to monitor the execution of a program, or to perform a post-mortem examination of the program state after an execution-time error.
• The run-time diagnostics detect such errors as: attempts to use uninitialized variables; incorrect use of subrange values; array subscripting errors; attempts to use nil pointer values or previously "disposed" memory; variant record semantics; and control statement semantics.
• In the event of a run-time error, Waterloo Pascal issues an error message stating at which line in the source program the error occurred, the name of any variables involved in the error, plus a procedure/function activation traceback, with a display of the scalar and string variables at each level.
• The compiler contains safeguards against "run-away" programs. Each installation may tailor this support to its own needs.
• The compiler produces two output files: a listing file and a diagnostics file. The listing file contains a list of the source program statements, plus the program output (the Pascal standard output file). If there were any compile-time errors, the error messages are inserted into the source listing at the appropriate place. The diagnostics file contains a summary of all diagnostic messages, plus a log of all interactive debugger output (if applicable).

Extensions to Pascal

• The Waterloo Pascal string extension consists of several new procedures and functions, combined with modifications to the type-compatibility rules in Pascal. The extension allows variable-length string data to be manipulated conveniently.
• The multiple concurrent process extension permits the simulation of multiprocessing directly in Pascal. The extension employs a message-passing abstraction (using Start, Send, Receive and Reply) similar to the one used in several real-time operating systems.
• The standard procedures reset and rewrite are extended to permit the specification of a system-dependent filename.
• There are numerous minor extensions to the Pascal language, including: extensions to the character set to accommodate systems on which the character set may not contain all required characters; additional general-purpose standard functions and procedures such as arcsin, arccos, arctan2, tan, RtoS ("Real to String") and StoR ("String to Real"); and the non-interactive debugging procedures TraceOn and TraceOff.

Documentation

The Waterloo Pascal Primer and Reference (Boswell, Grove and Mackie; ISBN 0-919884-45-8; WATCOM Publications Ltd., 1984) is the primary reference for the Waterloo Pascal compiler. In addition to being a reference manual, this book may also be used as a self-instruction manual or a course textbook. Each of the chapters in the Primer introduces a new topic in Pascal, and contains many examples and exercises.

Copies of this book may be purchased from WATCOM Publications Ltd. at the address shown below.

Availability

The Waterloo Pascal compiler is available in the following environments:

• IBM 370 architecture machines, under the VM/SP CMS and MVS (including TSO) operating systems