Programming Languages 1 (Com S 541)

This page gives access to information about the course offerings of ``Programming Languages 1'' as taught (in Spring 1993) by Gary T. Leavens for the Department of Computer Science at Iowa State University.

This is an old offering of the course. Information about the latest offering and other offerings is also available.

Information is available under the following headings.

Also available are the following.


This offering of the course was an attempt to really focus on progamming language design issues. Students did projects and designed languages in teams.

Course Description

Computer Science 541 studies modern programming languages, with an emphasis on design and semantics. This document specifies the course's general and specific objectives.

The study of programming languages is primarily concerned with the following questions:

Com S 541 addresses all these questions to some extent. In addressing the third question, however, we focus on the costs of programming in terms of human time and effort, not on machine efficiency (time and space costs) or on issues of compilation.

The catalog description of the course is as follows:

Survey of the goals and problems of language design. Formal and informal studies of a wide array of programming language features including type systems, naming, state, and control. Creative use of functional, object-oriented, declarative, concurrent and other programming paradigms. (3 credits).

Com S 541 is distinguished from Com S 342 (Principles of Programming Languages) is that Com S 342 concentrates on essential semantic concepts, studied with the use of interpreters (coded in a functional style). Com S 342 avoids mathematical formalisms, while in Com S 541, we will not shy away from them. In this version of Com S 541, we concentrate on mathematical semantics. In Com S 541 we aim to study modern functional and object-oriented languages, and assume that the graduate students are capable of dealing with the realistic versions of such languages. In Com S 541, we try to use mathematical tools to draw design lessons from our study of semantics, as opposed to simply understanding the features of modern languages.

Com S 541 is distinguished from Com S 641 (Semantics of Programming Languages) in that Com S 641 discusses particular formal semantic description techniques in depth, whereas a broader and less mathematically deep use of semantic description techniques is made in Com S 541; furthermore, an attempt is made in Com S 541 to show how to use these techniques in language design.

The course described here was developed with the help of Kelvin Nilsen. Final exams for similar courses at other universities were provided by Uday Redy (University of Illinois), John Mitchell (Stanford), Dan Friedman and J. Michael Ashley (Indiana), and Dave Gifford and Franklyn Turbak (MIT); these helped provide perspective on what is important for such a course. My early ideas for this course were formed as a teaching assistant in similar graduate courses led by Dave Gifford and John Guttag of MIT. Other ideas have been shaped by Barbara Liskov, Lawrence Flon, Per Brinch-Hansen, and students in previous editions of CS 541.

Administrative Information

Com S 541, ``Principles of Programming Languages,'' is usually taken by first year graduate students (if they have sufficient background). The class has a ``lecture'' that meets 3 times a week, for 50 minutes a time. It also has a discussion section that meets once a week (for 50 minutes) with a teaching assistant. There are usually 44 or 45 lecture meetings in a semester. The course carries 3 credit hours.


The formal prerequisite in the Iowa State catalog is successful completion of Com S 442 (Principles of Compiling); that is, successful completion of an undergraduate course in compiler construction.

The skills taught in Com S 442 relevant to Com S 541 include the ability to:

At Iowa State Com S 342 (Principles of Programming Languages) is a prerequisite for Com S 442, which means that you should already have some understanding of ``language design concepts,'' ``run-time implementation'' techniques, and ``major features of various programming languages.'' These topics are perhaps more directly relevant to Com S 541 than the material in Com S 442, but at many schools some of these topics are covered in a course on compiler construction. The skills of Com S 342 relevant to Com S 541 include the ability to:

If you do not have this background, especially if you are interested in research in programming languages, you should take Com S 342 or Com S 442 (preferably both if you want to do research in this area). Mere reading of texts on these subjects is not enough.


The general objectives for Com S 541 are divided into two parts: a set of essential of objectives and a set of enrichment objectives. The essential objectives will be helpful for your career as a computer scientist, regardless of your particular speciality; hence you are required to master them to some extent. You are not required to master the enrichment objectives, although you are encouraged to explore them both for their own sake and because learning more about those will help deepen your understanding of the essential objectives.

Essential Objectives

In general terms the essential objectives for Com S 541 are that you be able to:

You will be expected to complete all the tasks above without references, except writing programs and formally specifying languages.

Language design is fundamental to mathematics and science because a crucial step in solving a problem is designing an adequate notation for stating the problem (the specification) and expressing the solution. In computer science, unlike mathematics and the traditional sciences, because computers are general purpose tools, we tend to look at widely different problems. Problems from different application domains often come without a familiar or ready-made notation; thus the computer scientist often finds it convenient to develop a special-purpose notation. In developing such a special-purpose notation (e.g., a specification language or programming language) it is helpful to draw on the results of programming language research. These results will help you in generating plausible designs, in avoiding errors made by past language designers, in evaluating alternative designs, and in the detailed specification of your design. Perhaps more important, if your design is to be heavily used, you will need to know how to evaluate it, and what trade-offs exist among competing goals. Such justification of a design is a necessary step in convincing yourself and others that your design is good (or bad).

Notations that are similar to programming languages are found in every area of computer science. Besides specification languages, other similar notation systems include: user-interfaces, program libraries, formal models of computation, database query languages, operating system command languages and system call interfaces, mathematical logics, computer instruction sets, expert system shells, network protocols, and many others.

In addition, language design is challenging. Since it is one step removed from programming (you design notations that are used by programmers to write many different programs), the opportunities for good or ill are multiplied. Because of that, it is great fun!

Knowing how to solve problems using the different paradigms is important for several reasons. You can find solutions to problems more surely if you have many different ways to approach problems. In the twenty-first century you will not necessarily be programming in FORTRAN or C; if you can program in a language such as Smalltalk, C++, or Ada, or other new languages you will be much in demand. As parallel programming becomes more important, the use of functional and logic programming languages may increase. Already the use of object-oriented languages is increasing.

Even if you do not become a programmer, the ideas of the functional paradigm (function abstraction, infinite data structures, continuations, referential transparency) have important applications in all areas of computer science and in many other contexts such as mathematics and engineering. Similar comments hold true of the object-oriented and logic programming paradigms. For example, the idea of data abstraction is certainly a key concept in software engineering and even in contemporary mathematics (category theory). Knowing logic programming can help you in such diverse tasks as using a database query language and in careful specification of problems (which is necessary for problem solving in any domain).

Understanding the semantics of major features of programming languages is necessary to use such features and to design new languages. For example, if you want to program in an object-oriented language you need to understand inheritance and message passing. The better you understand such features, the better you will be able to program, reason about, and debug your programs. Formal methods (specification and verification) are becoming increasingly important in day to day programming at many companies, and a deep understanding of the semantics of programming languages is a great help in using formal methods. Without understanding the semantics of such features, you may also have difficulty discussing programming language ideas with others, and will have difficulty in reading the technical literature. If you are planning in specializing in some other area of computer science, you may someday need to read some of the literature on programming languages, either to use results from programming languages, or to apply ideas from your area to programming language research.

Enrichment Objectives

Enrichment objectives could be multiplied endlessly. Listed here are general statements of those that I tend to teach or that you may wish to investigate. The justification for each objective is included in this list.


In 1993 there were two course texts: David A. Watt's Programming Languages: Concepts and Paradigms (Prentice Hall International Series, 1990), with a supplement of Watt's Programming Languages: Syntax and Semantics (Prentice Hall International Series, 1991).

We also had a course packet with various readings.

Last update $Date: 1999/08/11 17:18:38 $
Gary T. Leavens
229 Atanasoff Hall
Department of Computer Science, Iowa State University
Ames, Iowa 50011-1040 USA