Modula-2 is a simple yet powerful programming language that is suitable for a wide variety of applications. It is based on Pascal, a successful programming language that was introduced in 1970 by Niklaus Wirth. During the 1970's Pascal became the most widely taught programming language and it gained acceptance in science and industry. In 1980 Dr. Wirth released the Modula-2 program ming language. Modula-2 is an evolution of Pascal. It improves on the successes of Pascal while adding the MODULE - a tool for ex pressing the relations between the major parts of programs. In ad dition Modula-2 contains low-level features for systems program ming and coroutines for concurrent programming. Programming languages are important because they are used to express ideas. Some programming languages are so limited that certain ideas can't be easily expressed. For example languages that lac k floating point arithmetic are inappropriate for scientific com putations. Languages such as Basic and Fortran that lack recur sion are unsuitable for text processing or systems programming. Sometimes a programming language is useable for a certain appli cation but it is far from ideal. A good example is the difficulty of writing large programs in pure Pascal. Pascal is a poor language for large jobs because it lacks facilities for partitioning a program viii Preface 6

This book is intended for the novice as well as for the experienced programmer who wants to learn Modula-2. We do not limit ourselves to just a description of Modula-2. Instead, we seek to familiarize the reader with the concept of algorithms and to show him/her how to implement algorithms in Modula-2. The programming language Modula-2 was developed by Niklaus Wirth (also the father of world-famous Pascal) and made public in 1978. Compared to other programming languages such as Ada, COBOL or PL/!, Modula-2 is a compact language, which makes it easy to learn. Nevertheless, Modula-2 contains all important language elements necessary for formulating complicated algorithms and for implementing the modern concepts of software engineering. Modula-2 is distinguished by a systematic structure that makes it possible to write easily readable programs. The language supports many of the principles of modern software engineering. All this makes Modula-2 a useful instrument for an introduction to the basics of programming. This textbook strives to establish a solid foundation in the techniques of programming with up-to-date methods of program development. Use of the programming language Modula-2 is reinforced with numerous hands-on exercises. This book does not presuppose any knowledge of programming, but it does require a certain ability in the realm of abstract thinking, some pleasure in problem solving, and a desire to come to terms with complex interrelationships.

This book is meant to be both an introduction to Modula-2 and a reference for that language. It is assumed that the reader is familiar with the mechanics of using text editors and compilers and has at least a nodding acquaintance with the use of pointers in simple data structures such as linked lists and trees. It is further assumed that once the basic facts associated with a given data type are clear, the reader will be able to decide which type is appropriate in a particular set of circumstances. To assist readers who have little previous programming experience, the material is presented in a easiest-to-hardest sequence.