Table Of ContentSpringer Books on Professional Computing
Edited by Henry Ledgard
Springer Books on Professional Computing
Computer Confidence: A Human Approach to Computers
Bruce D. Sanders. viii, 90 pages. 23 figures. 1984. ISBN 0-387-90917-6
The Unix System Guidebook: An Introductory Guide for Serious Users
Peter P. Sylvester. xi, 207 pages. 6 figures. 1984. ISBN 0-387-90906-0
The American Pascal Standard: With Annotations
Henry Ledgard. vii, 97 pages. 1984. ISBN 0-387-91248-7
Modula-2 for Pascal Programmers
Richard Gleaves. x, 145 pages. 18 figures. 1984. ISBN 0-387-96051-1
Richard Gleaves
Modula-2 for Pascal Programmers
Springer-Verlag
New York Berlin Heidelberg Tokyo
Series Editor
Henry Ledgard
Human Factors Ltd.
Leverett, MA 01054
U.S.A.
Computing Review Classification: D.3
Library of Congress Cataloging in Publication Data
Gleaves, Richard.
(Springer books on professional computing)
Modula-2 for Pascal programmers.
Includes index.
1. Modula-2 (Computer program language)
2. PASCAL (Computer program language) I. Title.
n. Title: Modula-Two for Pascal programmers.
QA76.73.M63G54 1984 001.64'24 84-13888
With 18 Figures.
© 1984 by Springer-Verlag New York Inc.
All rights reserved. No part of this book may be translated or reproduced in any form
without written permission from Springer-Verlag, 175 Fifth Avenue, New York, New
York 10010, U.S.A.
The use of general descriptive names, trade names, trademarks, etc., in this publication,
even if the former are not especially identified, is not to be taken as a sign that such
names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly
be used freely by anyone.
Media conversion by Scenic Computer Systems Corp., Redmond, Washington.
9 8 7 654 3 2 I
lSBN-13: 978-0-387-96051-7 e-lSBN-13: 978-1-4613-8531-8
DOl: 10.1007/978-1-4613-8531-8
Preface
This book describes the programming language Modula-2. It is written
for people who know the Pascal language and who wish to learn
Modula-2 in terms of their knowledge of Pascal.
The text is divided into three parts. Part 1 introduces concepts unique
to Modula-2 and thus new to Pascal programmers. Part 2 describes
differences from Pascal. Part 3 defines modules which provide basic
programming facilities. The appendices include a glossary and syntax
diagrams.
Please note that this book does not offer a complete description of the
Modula-2 language; it is intended to complement Niklaus Wirth's
definitive book Programming in Modula-2 (Springer-Verlag, 1983).
Some readers will recognize this book as being based upon the Volition
Systems Modula-2 User's Manual. Enough has changed to merit its
reappearance in this more dignified form: existing material has been
reorganized to improve clarity; new material has been added to improve
content.
This book was written with the ASE text editor. The text was
produced in camera-ready form on the Scenic LaserTezt composition
system.
I wish to thank the following people and organizations for their
contributions to the development of this book: Volition Systems, for
giving me the opportunity to write about Modula-2; Jim Merritt, for
reviewing an early draft; the Institut far Informatik, ETH Zarich, for
publishing a series of informative technical papers on Modula-2; and
finally, all the pioneer users of Volition Systems Modula-2, for their
patience and foresight and support.
Richard Gleaves
Del Mar, California
November 1983
Contents
Preface ............................................... v
Introduction ........................................ ix
Part 1 New Concepts ........................................ 1
1. Modules .............................................. 3
2. Separately Compiled Modules.................. 13
3. Program and Subprogram Modules ............ 21
4. Utility Modules .................................... 24
5. The Module Library .............................. 26
6. Low-level Programming ........................ 29
7. Coroutines and Interrupts ....................... 34
8. Procedure Variables .............................. 41
Part 2 Differences From Pascal ......................... 45
9. Vocabulary ......................................... 47
Identifiers ........................................ 47
Symbols & Reserved Words ...................... 48
Comments ........................................ 49
10. Constants .......................................... 50
Integers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50
Reals ............................................. 51
Characters........ . . . .. .. . .......... . .. .... ...... 51
Strings ........................................... 52
Sets .............................................. 53
11. Types ............................................... 54
Integers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54
Cardinals ......................................... 54
Reals ............................................. 55
Booleans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56
Characters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56
Enumerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 57
Subranges ....... , .............................. " 57
Arrays ........................................... 58
Records .......................................... 58
Vlll Contents
Sets .............................................. 59
Pointers .......................................... 60
12. Expressions ........................................ 61
Function Calls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62
Operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63
13. Statements ......................................... 64
Assignment ....................................... 65
Procedure Calls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 66
WHILE Statements ............................... 67
IF Statements .................................... 67
REPEAT Statements ............................. 68
FOR Statements........ . . . . . . . . . . . . . . . . . . . . . . . .. 68
WITH Statements ................................ 69
CASE Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69
LOOP jEXIT Statements ......................... 70
RETURN Statements.. . . . . . . . . . . . . . . . . . . . . . . . . .. 71
14. Procedures and Functions ....................... 73
Function Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 73
Open Array Parameters .......................... 74
15. Standard Procedures ............................. 76
16. Blocks ............................................... 79
Part 3 Utility Modules ..................................... 83
17. Standard I/O ...................................... 85
18. Text I/O ........................................... 89
19. File I/O ............................................. 96
20. Terminal I/O ..................................... 105
21. Storage Management ............................ 106
22. Subprogram Calls ............................... 107
, 23. Strings ............................................. 113
24. Format Conversion .............................. 116
25. Math Functions.................................. 118
App. A Glossary ............................................... 119
App. B Syntax Diagrams ..................................... 122
App. C Reserved Words and Symbols..................... 139
App. D Standard Identifiers ................................. 140
App. E ASCII Character Set................................ 141
Index ............................................... 143
Introduction
Modula-2 is a general-purpose language designed primarily for writing
software systems. The name Modula is short for "modular language".
Modula-2 is the third in a family of languages created by the Swiss
computer scientist Niklaus Wirth. The first language, Pascal, was
conceived as a teaching language, but achieved widespread use. The
second, Modula, was a special-purpose language designed for
programming small real-time control systems. Modula-2 emerged as a
synthesis of the systems programming capabilities of Modula and the
general utility of Pascal.
While it includes most of Pascal's features, Modula-2 differs from
Pascal in three ways:
• It extends Pascal upwards to encompass system design. Modula-2
is capable of expressing large software systems without requiring
support from an underlying operating system.
• It extends Pascal downwards to allow machine-level programming.
Modula-2 eliminates the need for assembly language in the lowest
levels of a computer system.
• It introduces minor changes to Pascal which simplify programming
and improve program readability and efficiency.
Modula-2, as its name suggests, is based on the concept of modules. A
module is a group of related procedures and data collectively known as
obiuu. A module allows some of its objects to be accessible outside the
module, but hides the existence of other objects from the rest of the
program.
Though conceptually simple, modules have a surprisingly wide scope of
application:
• Modules allow large programs to be structured in a more readable
fashion than is possible with languages like Pascal: small collections
of modules (sharing relatively few objects) replace the traditional
army of procedures interconnected by pages of global declarations.
• The ability of modules to separate a program into well-defined
parts provides a basis for separate compilation. Modula-2 defines
a special form of module which is compiled separately from a
program. Large programs can be divided into collections of
separately compiled modules; alternatively, separately compiled
modules can be placed in a library for use by different programs.
x In trod uction
• The ability of modules to contain and hide objects allows portable
programs to contain machine-dependent programming. Machine
level objects can be encapsulated in specific modules and thus
isolated to small parts of a program. These modules present only a
high-level interface - direct access to machine-level objects is
prevented. Therefore, when programs are moved to different
computers, the bulk of the software remains unchanged; only the
machine-dependent modules need rewriting.
• The ability of modules to define data types which hide their
internal structure encourages the use of a programming concept
known as "abstract data types". All operations on abstract data
types are performed via procedure calls; their data (or "state")
cannot be accessed directly. A familiar example of an abstract data
type is Pascal's predefined file type; however, Pascal is unable to
define new abstract data types.
Part 1 of this book presents modules and other concepts unique to
Modula-2 and thus new to Pascal programmers. Because it introduces
key language concepts, part 1 is organized as a tutorial.
Part 2 is comparatively light reading - it describes Modula-2's
differences from Pascal. Because it covers finer points in the language,
part 2 is organized for ease of reference.
Part 3 presents a set of utility modules which provides basic
programming facilities for Modula-2 programs. Example programs are
included to show how the modules are used.
Part 1. New Concepts
Part 1 introduces language concepts which are unique to Modula-2. It is
divided into eight chapters: Modules, Separately Compiled
Modules, Program and Subprogram Modules, Utility Modules,
The Module Library, Low-level Programming, Coroutines and
Interrupts, and Procedure Variables.
Modules are obviously the key concept in Modula-2: separate
compilation is accomplished with special forms· of modules; basic
programming facilities are provided by utility modules; facilities for
machine-level programming and interrupt handling are provided by
predefined modules. Of the new concepts, only procedure variables are
unrelated to modules; they follow from a new data type known as the
ftprocedure type".
Part 1 uses small Modula-2 programs to illustrate the new language
concepts; in doing so, it reveals syntactical differences from Pascal that
are not described until part 2. Fortunately, the new syntax differs only
slightly - you should have no problems understanding the programs.
