PASCAL Language Manual Ver 1 Sep83

This document is the "TOPS-20 PASCAL Language Manual" (AA-L315A-TM), published in September 1983. It serves as a reference guide for the PASCAL language elements and the PASDDT debugger implemented on the TOPS-20 operating system (versions V3.1 and V4.1), with PASCAL V1.0, LINK V3.1, and RMS V1.2. It is intended for readers already familiar with the PASCAL language.

The manual covers:

• PASCAL Overview: Introduces the language, program structure, lexical elements (character set, reserved words, identifiers, special symbols, delimiters), documentation, and the %INCLUDE directive.
• Data Types: Details the declaration of scalar (predefined like INTEGER, REAL, BOOLEAN, CHAR; user-defined like enumerated and subrange), structured (arrays, records, sets, files), and pointer types.
• Expressions: Explains arithmetic, relational, logical, and set operators, their precedence, and the scope of identifiers.
• Program Structure & Statements: Describes the program heading, declaration sections (LABEL, CONST, TYPE, VAR, VALUE), and various PASCAL statements, including compound, assignment, conditional (IF-THEN, IF-THEN-ELSE, CASE), repetitive (FOR, REPEAT, WHILE), WITH, GOTO, and procedure calls.
• Procedures and Functions: Covers predeclared and user-declared subprograms, external subprograms, parameters (value, variable, procedure/function, conformant arrays), and modules for separate compilation.
• Input and Output: Provides in-depth information on file characteristics (names, logical names, organization, access, record formats), and specific I/O procedures (CLOSE, FIND, GET, LINELIMIT, OPEN, PAGE, PUT, READ, READLN, RESET, REWRITE, WRITE, WRITELN, and terminal I/O).
• Using PASCAL on TOPS-20: Outlines the program development process (creating, compiling, loading, executing), file specifications, and PASCAL compiler commands and switches.
• PASDDT Debugger: Explains how to run the debugger, use symbolic values and scope, and its commands (ASSIGN, BREAK, CLEAR, DISPLAY, EXIT, HELP, PROCEED, REMOVE, SET, SHOW, TRACE).

PASCAL-20 Extensions: The manual highlights PASCAL-20's extensions to the proposed ISO standard, including:

• Exponentiation operator (**)
• Hexadecimal, octal, and binary integer constants
• Double-precision real data type
• Dollar sign ($) and underline (_) in identifiers
• External procedure and function declarations
• Additional functions: CARD, CLOCK, EXPO, SNGL, UNDEFINED
• REM operator
• OTHERWISE clause in the CASE statement
• File access procedures: OPEN, CLOSE, FIND
• Optional carriage control for output files
• Procedures: DATE, TIME, HALT, LINELIMIT
• Variable initialization
• Separate compilation using MODULE and the %INCLUDE directive
• Support for calling external FORTRAN subroutines.

Appendices offer further details on PASCAL messages, the ASCII character set, a syntax summary in Backus-Naur Form (BNF), a summary of PASCAL-20 extensions, ISO compliance, differences between PASCAL-20 and VAX-11 PASCAL, and procedure/function calling sequences.