What is most attractive about the Erlang programming language is that from the beginning it was designed to solve real and difficult problems, and to do it in an elegant and powerful way. It is also a small language, which makes writing tools for it much more practical than for larger language such as Java or C++.
This book is written for experienced programmers, but not necessarily those that have any prior exposure to Erlang or even functional programming languages in general. The book consists of two parts. The first should be read sequentially, like a textbook. The second part, however, can be read in any order as you need the informaton. The following is a listing of the chapters and a brief description of what you'll find in each.
The first part of the book consists of the first eleven chapters, and describes the core parts of the Erlang language.
1. Introduction - Gives a high-level overview of the characteristics and features that have made Erlang so successful, provides insight into the context in which the language was designed, and describes how this influenced its current shape. Case studies show how Erlang is actually used, comparing it with other languages and highlighting its strengths.
2. Erlang Basics - Covers the basics of Erlang. Some of this will be elementary for experienced programmers, and some will not, such as the fact that you can assign to each variable only once. The chapter starts with defining the basic Erlang data types, and concludes by showing how to define Erlang functions and place them into modules to create programs.
3. Sequential Erlang - An important topic here is recursion, which is perhaps the most useful and powerful of all techniques usually found in a functional language. It allows a programmer to traverse a data structure via successive calls to the same function. Also exception-handling mechanisms are covered here as is the debugger.
4. Concurrent Programming - Concurrency is when different functions execute in parallel without affecting each other unless explicitly programmed to do so. The ability of the runtime system to scale concurrency to levels such that there can be thousands of processes running in parallel with a small memory footprint differentiates Erlang from other concurrent programming languages. This chapter discusses all of these matters.
5. Process Design Patterns - Many Erlang processes will fall into one of three categories - client/servers, finite state machines, and event handlers. This chapter looks at examples of process design patterns, explaining how they can be used to program each of these three types of processes. The OTP framewor is also part of this topic, but OTP doesn't get discussed until chapter 12.
6. Process Error Handling - Erlang has simple but powerful constructs built into the language's concurrency model. These constructs allow processes to monitor each other's behavior and to recover from software faults, and are discussed here.
7. Records and Macros - In the first part of this chapter you will learn about records, which make code evolution easier to achieve. The key to this is the fact that records provide data abstraction. Macros, the other topic in this chapter, allow you to write abbreviations that are expanded by the Erlang preprocessor. Macros can be used to make programs more readable, to extend the language, and to write debugging code. The chapter concludes by describing the include directive, by which header files containing macro and record definitions are used in Erlang projects.
8. Software Upgrade - The software upgrade mechanism relies on a set of simple but powerful constructs upon which more powerful tools are built. These upgrade tools are used in pretty much every Erlang-based system where downtime has to be reduced to a minimum. These topics are explored here.
9. More data types and high-level constructs - The various language features covered in this chapter, many of them derived from functional programming languages, are tools that will improve the productivity of a working Erlang programmer. The topics are: funs and higher-order functions, list comprehensions, binaries, and serialization.
10. ETS and Dets Tables - To handle fast searches, Erlang provides two mechanisms. This chapter introduces Erlang Term Storage (ETS) and Disk Erlang Term Storage (Dets), two mechanisms for memory and disk-efficient storage and retrieval of large groups of data. Erlang also provides a full database application, Mnesia, which is covered in chapter 13.
11. Distributed Programming in Erlang - This chapter explores the theory behind distributed systems and shows how it is applied to Erlang-based systems. Erlang distribution is built into the language, and can be completely transparent to the user.
The rest of the book can be read in any order as needed:
12. OTP Behaviors - OTP behaviors provide library modules that implement the most common concurrent design patterns. Behind the scenes the library modules insure that errors and special cases are handled in a consistent way. As a result, OTP behaviors provide a set of standardized building blocks. This subject is a large one and this chapter is only an introduction.
13. Introducing Mnesia - Mnesia is a powerful database that is part of the standard Erlang distribution. It merges the efficiency and simplicity of ETS and Dets tables with the Erlang distribution and adds a transaction layer on top. Again, this is a large subject and this chapter acts only as an introduction.
14. GUI Programming with Erlang - GUIs are not one of Erlang's strengths, but it does have a cross-platform GUI programming system, wxErlang, which is a binding of the wxWidgets system. This chapter introduces wxWidgets and explains its Erlang binding. After describing the event-handling mechanism in wxErlang, a scaled-down blog example is presented using it. This chapter concludes with a number of pointers for learning more about wxWidgets and wxErlang, and a series of exercises to improve and extend the running example.
15. Socket Programming - Sockets allow programs written in any language to exchange data on different computers by exchanging byte streams transmitted using the protocols of the Internet Protocol. Sometimes even Erlang programs must rely on such a lower-level mechanism for communication.
16. Interfacing Erlang with Other Programming Languages - Discusses how to link Erlang with a C program, Java program, or the Unix shell.
17. Trace BIFs, the dbg Tracer, and Match Specifications - Explains in depth how all aspects of Erlang systems can be traced without degrading their performance.
18. Types and Documentation - This chapter shows how you can write down the types of functions as a part of their formal documentation in Erlang, using the EDoc documentation framework. In addition, what you write down as the type of a function can be checked for consistency against the function definition using the TypEr tool, which is also discussed here.
19. EUnit and Test-Driven Development - In this chapter, the EUnit tool, which gives you a framework for unit testing in Erlang, is discussed. It is shown in action and there is a discussion on how it supports test-driven development.
20. Styles and Efficiency - Summarizes design guidelines and programming strategies to use when developing Erlang systems. The chapter also covers common mistakes and inefficiencies and looks at memory handling and profiling.
Appendix A - Using Erlang- Recommends tools to help you in Erlang softare development and also lists resources for programmers such as websites and books.
I've spent some considerable time with both Haskell and Erlang, two very good functional languages. When it comes to high concurrency and networking applications, Erlang is probably the best choice. However, I still like Haskell because I've found it easier to handle when writing multimedia applications, which is often my focus. You could take a long time to come to your own conclusions, but I found this book and the recently published book on Haskell,
Real World Haskell, to cut that time down extensively by explaining the features of both languages so well. I therefore highly recommend this book to people trying to make up their minds about Erlang and those that have made up their minds and now need a clear book on the subject.
