Erlang编程入门与实践指南

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《Erlang编程指南》是一本由 Francesco Cesarini 和 Simon Thompson 合著的专业级IT书籍，主要聚焦于Erlang编程语言的深入理解和实践。Erlang是一种函数式编程语言，以其并行性和分布式计算能力而闻名，特别适合构建高并发、低延迟的应用程序，如电信系统、金融交易处理和实时系统。这本书旨在为读者提供全面的Erlang语言基础，包括语法特性、并发模型、模块系统以及高级主题，如Erlang OTP（Object-Orientation Programming in Erlang）框架和错误处理。书中涵盖了以下关键知识点： 1. 语言介绍：首先，读者将了解Erlang的历史背景、设计理念和语言特性，如轻量级进程、模式匹配、尾递归优化等，这些都是Erlang高效并发的核心。 2. 并发与分布计算：章节中详细阐述了Erlang的并发模型，包括轻量级进程（gen_server, gen_fsm, gen_event）的使用，以及如何利用Erlang的actor模型实现分布式系统。 3. 模块系统与包管理：书中会介绍Erlang的模块结构和命名空间，以及如何组织和管理大型项目中的代码库。 4. Erlang虚拟机（EVM）：这部分将探讨Erlang运行时环境的工作原理，包括垃圾回收机制、线程池和内存管理。 5. Erlang OTP框架：这是Erlang开发的重要部分，作者会讲解OTP的设计原则、应用架构、常见行为和常见工具，如gen_server行为和Supervisor监控系统。 6. 错误处理与调试：如何在Erlang中有效地处理错误、日志记录和调试，以提高系统的稳定性和可维护性。 7. 实战项目示例：书中包含若干实用的编程示例和项目，帮助读者通过实践加深对Erlang的理解和应用。 8. 扩展与社区支持：最后，本书还会介绍Erlang的生态系统，如Erlang BEAM虚拟机的性能优化，以及如何与其他语言和工具集成，如Node.js、Redis等。《Erlang编程指南》是一本理想的入门指南和参考书，无论是对初学者还是有经验的开发者，都能从中受益匪浅，提升在高并发和分布式环境中编程的能力。无论是希望通过Erlang进行系统开发的工程师，还是想要了解函数式编程思想的读者，都值得阅读和研究这本书。

Preface

What made us start writing this book in the first place is the enthusiasm we share for

Erlang.

We wanted to help get the word out, giving back a little of what the community

has given to us. Although we both got into Erlang for very different reasons, the end

result was the same: lots of fun hours doing lots of fun stuff at a fraction of the effort

it would have taken with other languages. And best of all, it is not a tool we use for

hobby projects, but one we use on a daily basis in our real jobs!

Francesco: Why Erlang?

The year was 1994. While studying computer science at Uppsala University, one of the

courses I took was on parallel programming. The lecturer held up the first edition of

Concurrent Programming in Erlang (Prentice Hall) and said, “Read it.” He then held

up a handout and added, “These are the exercises, do them,” after which Erlang barely

got a mention; it was quickly overshadowed with the theory of threads, shared memory,

semaphores, and deadlocks.

As the main exercise for this course, we had to implement a simulated world inhabited

by carrots, rabbits, and wolves. Rabbits would roam this world eating carrots that grew

in random patches. When they had eaten enough carrots, the rabbits would get fat and

split in two. Wolves ran around eating up the rabbits; if they managed to catch and eat

enough rabbits, they would also get fat and split. Rabbits and wolves within a certain

distance of each other would broadcast information on food and predators. If a rabbit

found a carrot patch, other rabbits would quickly join him. If a wolf found a rabbit,

the pack would start chasing it.

The final result was amusingly fun to watch. The odd rabbit would run straight into a

group of wolves, while others would run in other directions, sometimes stopping to

grab a carrot en route. Every carrot patch, rabbit, and wolf was represented as an Erlang

process communicating through message passing.

The exercise took me about 40 hours to solve. Although I enjoyed using Erlang and

was positively surprised at the simplicity of its concurrency model and lack of OS

threads for every process, I did not think that much of it right there and then. After all,

it was one of the dozen or so languages I had to learn for my degree. Having used ML

in my functional programming courses and ADA in my real-time programming courses,

for me Erlang was just another language in the crowd. That changed a few months later

when I started studying object-oriented programming.

In the object-oriented (OO) programming course, we were given the same simulated

world lab but had to solve it with Eiffel, an OO language our new lecturer insisted was

ideal for simulations. Although I had already solved the same problem and was able to

reuse a good part of the algorithms, it took me and a fellow student 120 man-hours to

solve.

This was the eye-opener that led me to believe the declarative and concurrent features

in Erlang had to be the direction in which software development was heading. At the

time, I was not sure whether the language that would lead the way in this paradigm

shift was going to be Erlang, but I was certain that whatever language it was, it would

be heavily influenced by Erlang and its ancestors. I picked up the phone and called Joe

Armstrong, one of the inventors of Erlang. A week later, I visited the Ericsson Computer

Science Lab for an interview, and I have never looked back.

Simon: Why Erlang?

I have worked in functional programming since the early 1980s, and have known about

Erlang ever since it was first defined about 20 years ago. What I find most attractive

about Erlang is that it’s a language that was designed from the start to solve real and

difficult problems, and to do it in an elegant and powerful way. That’s why we’ve seen

Erlang used in more and more systems in recent years.

It’s also a small language, which makes writing tools for it much more practical than

for a language such as Java, C++, or even Haskell. This, and the quality of the libraries

we’ve been able to build on in our work, has helped the functional programming group

at Kent to be very productive in implementing the Wrangler refactoring tool for Erlang.

Who Should Read This Book?

We have written this book to introduce you to programming in Erlang. We don’t expect

that you have programmed in Erlang before, nor do we assume that you are familiar

with functional programming in other languages.

We do expect you to have programmed in Java, C, Ruby, or another mainstream lan-

guage, and we’ve made sure that we point out to you where Erlang differs from what

you’re used to.

xvi | Preface

How to Read This Book

We wrote this book in two parts, the first to be read sequentially and the second can

be read concurrently (or sequentially in whatever order you like), as the chapters are

independent of each other.

The first 11 chapters of the book cover the core parts of Erlang:

• Chapter 1 gives a high-level introduction to the language, covering its key features

for building high-availability, robust concurrent systems. In doing this, we also

describe how Erlang came to be the way it is, and point out some of its high-profile

success stories, which explain why you may want to adopt Erlang in one of your

projects.

• The basics of sequential programming in Erlang are the subject of Chapters 2 and

3. In these chapters, we cover the central role of recursion in writing Erlang pro-

grams, as well as how single assignment in Erlang is quite different from the way

variables are handled in other languages, such as C and Java.

• While covering sequential programming, we also introduce the basic data types of

Erlang—numbers, atoms, strings, lists, and tuples—comparing them with similar

types in other languages. Other types are covered later: records in Chapter 7, and

function types and binaries in Chapter 9. Large-scale storage in ETS tables is the

topic of Chapter 10.

• Erlang’s distinctiveness comes to the fore in Chapters 4–6, which together cover

the concurrent aspects of Erlang, embodied in message passing communication

between concurrently executing processes running in separate memory spaces.

• It is possible to “hot-swap” code in a system, supporting software upgrades in run-

ning systems: this is the topic of Chapter 8.

• To conclude this part of the book, we cover distributed programming in Chap-

ter 11. This allows different Erlang runtime systems (or nodes), which might be

running on the same or different machines, to work together and interact as a

distributed system.

In the remaining chapters, we cover a variety of different topics largely independent of

each other. These include the following:

• The Open Telecom Platform (OTP) gives a set of libraries and design principles

supporting the construction of robust, scalable systems in Erlang; this is the subject

of Chapter 12.

• The Erlang distribution contains some standard computing applications: we cover

the Mnesia database in Chapter 13 and the wxErlang GUI programming library in

Chapter 14.

Preface | xvii

• Erlang distribution gives one mechanism for linking Erlang systems to each other.

Chapter 15 shows how Erlang supports programming across the Internet using

sockets, and Chapter 16 covers the various ways in which Erlang can interwork

with systems written in C, Java, and Ruby, as well as many other languages.

• The standard Erlang distribution comes with a number of very useful tools, and

we cover some of these next. Chapter 17 explains in depth how all aspects of Erlang

systems can be traced without degrading their performance, and Chapter 18 covers

tools for checking the correctness of programs, and for constructing documenta-

tion for Erlang systems. Unit testing, and how it is supported by EUnit, is the

subject of Chapter 19.

• The last chapter, Chapter 20, looks at how to write programs that are elegant,

readable, and efficient, and pulls together into one place much of the accumulated

experience of the Erlang community.

The Appendix covers how to get started with Erlang, how to use the Erlang shell,

popular tools for Erlang, and how to find out more about Erlang.

Each chapter is accompanied by a set of exercises, and you can download all the code

in this book from its website:

http://www.erlangprogramming.org

The website also has references to further reading as well as links to the major sites

supporting the Erlang community.

wrote this book to be compatible with Erlang Release 13 (R13-B). Most of the

features we describe will work with earlier releases; known incompatibilities with more

recent earlier releases are detailed on our website.

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, filenames, file extensions, and occasionally, emphasis

and keyword phrases.

Constant width

Indicates computer coding in a broad sense. This includes commands, options,

variables, attributes, keys, requests, functions, methods, types, classes, modules,

properties, parameters, values, objects, events, event handlers, XML and XHTML

tags, macros, and keywords.

Constant width bold

Indicates commands or other text that the user should type literally.

xviii | Preface

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