Although “Concepts, Techniques, and Models of Computer Programming” by Peter Van Roy and Seif Haridi looks intimidatingly big at around 900 pages, I found it surprisingly easy to read. It has a good balance of theoretical and practical descriptions of the concepts covered by it. It has a cohesive overview of the major programming styles in a manner that I have not seen in any other book. I would rank it as a must-read for the serious programmer along with classics like “The Art of Computer Programming” and “Structure and Interpretation of Computer Programming”.
The authors introduce various models of computation that cover the declarative and imperative styles of programming, including concurrent variants of each style. The declarative (or stateless) models include functional and logic programming while the imperative (or stateful) models include object-oriented programming. The authors also introduce some specialised models, for example, for distributed programming and constraint programming. All of these models are introduced using a single multi-paradigm programming language named “Oz”, that was developed by the research groups that the authors belong to and that is implemented by the Mozart programming system. Oz defines a small kernel language that provides the minimal support needed for each model and then defines linguistic abstractions and provides syntactic sugar that makes it convenient to programme in that model. In addition, the authors also provide an overview of a representative programming language for some of the models, including Haskell, Erlang, Java and Prolog.
It is obvious that the authors prefer the declarative computational model over the others, but they are honest and pragmatic enough to admit that for at least some programmes, explicit state simplifies the code and makes it more efficient. This is a refreshing change from some authors who insist that functional programming, say, is all that you should ever need and scoff at the mention of having the need to use explicit state for some programming needs. I fully agree with the authors that while explicit state cannot be avoided in some cases, one should try to write as much code as possible using the declarative model since it makes it easier to reason about the programme and presents more opportunities for optimisation to the compiler or interpreter.
One of the neat things I learnt from the declarative model presented by the authors is the concept of a “data-flow variable”. A variable is allowed to be unbound in addition to being bound to a single value - if a part of a programme tries to access the value of such an unbound variable in an expression, it is suspended till the time that some other part of the computation binds a value to the variable. This allows simple and reliable concurrency to be programmed in a very neat manner. Another new thing for me was the concept of a “secure variable”.
The authors make concurrent programming look much less intimidating and more reliable using data-flow variables and message-passing, though they also cover the kind of shared-state concurrent programming using monitors provided by programming languages like Java. The book also covers determining the space and time efficiency of procedures, proving programme correctness, creating secure ADTs (Abstract Data Types), implementing transactions, providing fault tolerance, etc. You have to read the book to see how expansive the coverage really is and how extensive the bibliography is (should you get curious and decide to explore more about a given topic). This book is not for the complete newcomer to programming though - you have to have had some experience in programming and preferably some prior exposure to different styles of programming to fully appreciate the material presented in the book. As always for such a book, you should definitely try out and play with the given examples in Mozart and at least attempt some of the exercises to really benefit from the book.
There are some minor irritants in the book. For example, in the preface and throughout the book the authors keep referring to “the book's web site” but I could not find a single place where the URL of the web site is provided! You have to use a search engine to find out that this page is most likely the intended place. The interactive development environment of the Mozart programming system is based on Emacs and I had to first download and install this beast (that I had managed to avoid all these years) before I could use Mozart. I am not sure if it is the fault of LaTeX or the way the authors have used this tool, but most of the figures are not close to the places from where they are referenced, making you flip back and forth unnecessarily between pages. Lastly, I personally thought that for at least some of the models (notably explicit-state and object-oriented), the support in Oz looks awkward unlike that for the other models.
All of these irritants can easily be overcome and I would therefore recommend this book to anyone seriously interested in computer programming.