Programming Language Pragmatics 4th Edition

Book Preface

A course in computer programming provides the typical student’s first exposure to the field of computer science. Most students in such a course will have used computers all their lives, for social networking, email, games, web browsing, word processing, and a host of other tasks, but it is not until they write their first programs that they begin to appreciate how applications work. After gaining a certain level of facility as programmers (presumably with the help of a good course in data structures and algorithms), the natural next step is to wonder how programming languages work. This book provides an explanation. It aims, quite simply, to be the most comprehensive and accurate languages text available, in a style that is engaging and accessible to the typical undergraduate. This aim reflects my conviction that students will understand more, and enjoy the material more, if we explain what is really going on.

In the conventional “systems” curriculum, the material beyond data structures (and possibly computer organization) tends to be compartmentalized into a host of separate subjects, including programming languages, compiler construction, computer architecture, operating systems, networks, parallel and distributed computing, database management systems, and possibly software engineering, object-oriented design, graphics, or user interface systems. One problem with this compartmentalization is that the list of subjects keeps growing, but the number of semesters in a Bachelor’s program does not. More important, perhaps, many of the most interesting discoveries in computer science occur at the boundaries between subjects. Computer architecture and compiler construction, for example, have inspired each other for over 50 years, through generations of supercomputers, pipelined microprocessors, multicore chips, and modern GPUs.

Over the past decade, advances in virtualization have blurred boundaries among the hardware, operating system, compiler, and language run-time system, and have spurred the explosion in cloud computing. Programming language technology is now routinely embedded in everything from dynamic web content, to gaming and entertainment, to security and finance.

Increasingly, both educators and practitioners have come to emphasize these sorts of interactions. Within higher education in particular, there is a growing trend toward integration in the core curriculum. Rather than give the typical student an in-depth look at two or three narrow subjects, leaving holes in all the others, many schools have revised the programming languages and computer organization courses to cover a wider range of topics, with follow-on electives in various specializations. This trend is very much in keeping with the ACM/IEEECS Computer Science Curricula 2013 guidelines [SR13], which emphasize the need to manage the size of the curriculum and to cultivate both a “system-level perspective” and an appreciation of the interplay between theory and practice. In particular, the authors write,

Graduates of a computer science program need to think at multiple levels of detail and abstraction. This understanding should transcend the implementation details of the various components to encompass an appreciation for the structure of computer systems and the processes involved in their construction and analysis [p. 24]. On the specific subject of this text, they write Programming languages are themedium through which programmers precisely describe concepts, formulate algorithms, and reason about solutions. In the course of a career, a computer scientist will work with many different languages, separately or together. Software developers must understand the programming models underlying different languages and make informed design choices in languages supporting multiple complementary approaches. Computer scientists will often need to learn new languages and programming constructs, and must understand the principles underlying how programming language features are defined, composed, and implemented. The effective use of programming languages, and appreciation of their limitations, also requires a basic knowledge of programming language translation and static program analysis, as well as run-time components such as memory management [p. 155]. The first three editions of Programming Language Pragmatics (PLP) had the good fortune of riding the trend toward integrated understanding. This fourth edition continues and strengthens the “systems perspective” while preserving the central focus on programming language design.

At its core, PLP is a book about how programming languages work. Rather than enumerate the details of many different languages, it focuses on concepts that underlie all the languages the student is likely to encounter, illustrating those concepts with a variety of concrete examples, and exploring the tradeoffs that explain why different languages were designed in different ways. Similarly, rather than explain how to build a compiler or interpreter (a task few programmers will undertake in its entirety), PLP focuses on what a compiler does to an input program, and why. Language design and implementation are