lua编程第四版书签版：快速查阅指南

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《Programming in Lua 4th Edition》是一本由Roberto Ierusalimschy编著的专业级编程指南，专为Lua语言的开发者设计。这本书是第四版更新，最新版本日期为2017年3月18日（build 21），提供给Eric Taylor，邮箱地址为jdslkgjf.iapgjflksfg@yandex.com，具有独家使用权。此书装帧简洁，旨在帮助读者掌握Lua语言的基础知识与实践技巧。本书分为多个章节，旨在逐步引导学习者进入Lua的世界。首先，"Getting Started"部分介绍了如何开始编程，包括如何理解和处理Lua中的"Chunks"（代码块）。书中详细解释了Lua的一些基本语法规则，比如全局变量的使用、不同类型和值的概念，以及对"Nil"类型的介绍。接着，作者深入探讨了逻辑运算，包括布尔值和比较运算符，还提及了Lua内置的数学库，如随机数生成器和数值处理函数，以及处理数值转换和运算优先级的问题。特别提到了Lua在处理整数之前的一些特性。 "Strings"章节涵盖了字符串处理的各个方面，包括如何创建和处理字符串，不同类型的字符串表示方法，以及字符串库的使用。此外，书中还讲解了Unicode字符集在Lua中的支持。 "Tables"是Lua的核心数据结构之一，书中讲解了如何使用表作为索引、构造数组和列表，以及如何遍历和安全地访问表中的元素。此外，还介绍了Lua的表格库，以增强表的操作功能。 "Functions"是编程语言的重要组成部分，书中讨论了如何定义、调用和理解函数，以及在Lua中实现多返回值和函数式编程的概念。这对于理解和实现复杂程序逻辑至关重要。在"Interlude: The Eight-Queen Puzzle"这一插曲中，作者可能会通过一个经典问题来演示Lua的实际应用和解决问题的能力，让读者更好地理解和运用所学知识。《Programming in Lua 4th Edition》是一本实用且深入的教程，适合想要学习或提升Lua技能的程序员，无论是初学者还是经验丰富的开发者，都能从中找到有价值的内容。书中丰富的例子和深入的理论结合，确保了学习者能够扎实地掌握Lua语言。

Table of Contents

1. Getting Started ................................................................................................................ 4

Chunks ...................................................................................................................... 4

Some Lexical Conventions ........................................................................................... 6

Global Variables ......................................................................................................... 7

Types and Values ........................................................................................................ 7

Nil .................................................................................................................... 8

Booleans ............................................................................................................ 8

The Stand-Alone Interpreter .......................................................................................... 9

2. Interlude: The Eight-Queen Puzzle .................................................................................... 12

3. Numbers ....................................................................................................................... 15

Numerals .................................................................................................................. 15

Arithmetic Operators .................................................................................................. 16

Relational Operators .................................................................................................. 17

The Mathematical Library ........................................................................................... 18

Random-number generator .................................................................................. 18

Rounding functions ............................................................................................ 18

Representation Limits ................................................................................................. 19

Conversions .............................................................................................................. 21

Precedence ............................................................................................................... 22

Lua Before Integers ................................................................................................... 22

4. Strings ......................................................................................................................... 24

Literal strings ............................................................................................................ 24

Long strings ............................................................................................................. 25

Coercions ................................................................................................................. 26

The String Library ..................................................................................................... 27

Unicode ................................................................................................................... 29

5. Tables .......................................................................................................................... 33

Table Indices ............................................................................................................ 33

Table Constructors ..................................................................................................... 35

Arrays, Lists, and Sequences ....................................................................................... 36

Table Traversal ......................................................................................................... 38

Safe Navigation ......................................................................................................... 38

The Table Library ..................................................................................................... 39

6. Functions ...................................................................................................................... 42

Multiple Results ........................................................................................................ 43

Variadic Functions ..................................................................................................... 45

The function table.unpack .................................................................................... 47

Proper Tail Calls ....................................................................................................... 48

7. The External World ........................................................................................................ 50

The Simple I/O Model ............................................................................................... 50

The Complete I/O Model ............................................................................................ 53

Other Operations on Files ........................................................................................... 54

Other System Calls .................................................................................................... 55

Running system commands ................................................................................. 55

8. Filling some Gaps .......................................................................................................... 57

Local Variables and Blocks ......................................................................................... 57

Control Structures ...................................................................................................... 58

if then else ....................................................................................................... 58

while ............................................................................................................... 59

repeat ............................................................................................................. 59

Numerical for ................................................................................................... 60

Chapter 1. Getting Started

To keep with tradition, our first program in Lua just prints "Hello World":

print("Hello World")

If you are using the stand-alone Lua interpreter, all you have to do to run your first program is to call the

interpreter —usually named lua or lua5.3— with the name of the text file that contains your program.

If you save the above program in a file hello.lua, the following command should run it:

% lua hello.lua

As a more complex example, the next program defines a function to compute the factorial of a given

number, asks the user for a number, and prints its factorial:

-- defines a factorial function

function fact (n)

if n == 0 then

return 1

else

return n * fact(n - 1)

end

print("enter a number:")

a = io.read("*n") -- reads a number

print(fact(a))

Chunks

We call each piece of code that Lua executes, such as a file or a single line in interactive mode, a chunk.

A chunk is simply a sequence of commands (or statements).

A chunk can be as simple as a single statement, such as in the “Hello World” example, or it can be composed

of a mix of statements and function definitions (which are actually assignments, as we will see later), such

as the factorial example. A chunk can be as large as we wish. Because Lua is used also as a data-description

language, chunks with several megabytes are not uncommon. The Lua interpreter has no problems at all

with large chunks.

Instead of writing your program to a file, you can run the stand-alone interpreter in interactive mode. If

you call lua without any arguments, you will get its prompt:

% lua

Thereafter, each command that you type (such as print "Hello World") executes immediately after

you enter it. To exit the interactive mode and the interpreter, just type the end-of-file control character

(ctrl-D in POSIX, ctrl-Z in Windows), or call the function os.exit, from the Operating System

library —you have to type os.exit().

Starting in version 5.3, we can enter expressions directly in the interactive mode, and Lua will print their

values:

Getting Started

% lua

> math.pi / 4 --> 0.78539816339745

> a = 15

> a^2 --> 225

> a + 2 --> 17

In older versions, we need to precede these expressions with an equals sign:

% lua5.2

> a = 15

> = a^2 --> 225

For compatibility, Lua 5.3 still accepts these equals signs.

To run that code as a chunk (not in interactive mode), we must enclose the expressions inside calls to

print:

print(math.pi / 4)

a = 15

print(a^2)

print(a + 2)

Lua usually interprets each line that we type in interactive mode as a complete chunk or expression. How-

ever, if it detects that the line is not complete, it waits for more input, until it has a complete chunk. This

way, we can enter a multi-line definition, such as the factorial function, directly in interactive mode. How-

ever, it is usually more convenient to put such definitions in a file and then call Lua to run the file.

We can use the -i option to instruct Lua to start an interactive session after running a given chunk:

% lua -i prog

A command line like this one will run the chunk in the file prog and then prompt for interaction. This is

especially useful for debugging and manual testing. At the end of this chapter, we will see other options

for the stand-alone interpreter.

Another way to run chunks is with the function dofile, which immediately executes a file. For instance,

suppose we have a file lib1.lua with the following code:

function norm (x, y)

return math.sqrt(x^2 + y^2)

end

function twice (x)

return 2.0 * x

end

Then, in interactive mode, we can type this code:

> dofile("lib1.lua") -- load our library

> n = norm(3.4, 1.0)

> twice(n) --> 7.0880180586677

The function dofile is useful also when we are testing a piece of code. We can work with two windows:

one is a text editor with our program (in a file prog.lua, say) and the other is a console running Lua

Getting Started

in interactive mode. After saving a modification in our program, we execute dofile("prog.lua")

in the Lua console to load the new code; then we can exercise the new code, calling its functions and

printing the results.

Some Lexical Conventions

Identifiers (or names) in Lua can be any string of letters, digits, and underscores, not beginning with a

digit; for instance

i j i10 _ij

aSomewhatLongName _INPUT

You should avoid identifiers starting with an underscore followed by one or more upper-case letters (e.g.,

_VERSION); they are reserved for special uses in Lua. Usually, I reserve the identifier _ (a single under-

score) for dummy variables.

The following words are reserved; we cannot use them as identifiers:

and break do else elseif

end false for function goto

if in local nil not

or repeat return then true

until while

Lua is case-sensitive: and is a reserved word, but And and AND are two different identifiers.

A comment starts anywhere with two consecutive hyphens (--) and runs until the end of the line. Lua

also offers long comments, which start with two hyphens followed by two opening square brackets and

run until the first occurrence of two consecutive closing square brackets, like here:

--[[A multi-line

long comment

]]

A common trick that we use to comment out a piece of code is to enclose the code between --[[ and

--]], like here:

--[[

print(10) -- no action (commented out)

--]]

To reactivate the code, we add a single hyphen to the first line:

---[[

print(10) --> 10

--]]

In the first example, the --[[ in the first line starts a long comment, and the two hyphens in the last line

are still inside that comment. In the second example, the sequence ---[[ starts an ordinary, single-line

comment, so that the first and the last lines become independent comments. In this case, the print is

outside comments.

Lua needs no separator between consecutive statements, but we can use a semicolon if we wish. Line

breaks play no role in Lua's syntax; for instance, the following four chunks are all valid and equivalent:

Long comments can be more complex than that, as we will see in the section called “Long strings”.

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