Then in Section 4 we see a relatively new trend in pro­ Even on "A Grand Tour" one cannot afford to visit gramming languages, the abstract data type. The lan­ all of the interesting spots. So too with an anthology on guages CLU and Euclid were designed (in part) to in­ programming languages, I could not afford to include corporate this concept of good software design into a all of the interesting articles. The arena of program­ programming language. Both languages are imple­ ming languages is a marvelously rich and diverse field. mented and are actively being used. Another major The objective of this work is to present an organized trend in programming languages today is the notion of collection of readable articles and language reference concurrent execution which is the subject of Section S. materials for the student of programming languages. Advances in hardware have made this concept a reality. My original purpose in creating this book was to use it Now we are beginning to see how programming lan­ for a university course on programming languages. guages are adapting to the need to express concurrency. Since then I've discovered that professional computer Concurrent-Pascal is one such language which takes scientists will also find it useful and entertaining.