Lua 5.3 教程：Programming in Lua 第四版

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"Programming in Lua 4th Edition with index 是一本专注于Lua编程语言的最新教程，涵盖了Lua 5.3版本的新特性和更新。作者是Roberto Ierusalimschy，由Feisty Duck Digital出版。这本书是学习Lua语言的理想选择，适合初学者和有经验的程序员。" 本文档详细介绍了Lua编程语言的基础知识，分为多个章节，每个章节深入探讨了不同的主题。以下是主要知识点的概述： 1. **Getting Started**：这部分介绍了如何开始使用Lua，讲解了Lua中的"chunks"，即程序的基本组织单元。还讨论了Lua的一些词法约定，如变量声明、全局变量以及不同类型的值。 2. **Some Lexical Conventions**：详细阐述了Lua的词汇规则，包括如何定义变量、常量以及对大小写敏感性的处理。 3. **Numbers**：讲解了Lua中的数值类型，包括数值的表示形式（十进制、十六进制等）、算术运算符、关系运算符，以及`math`库的使用，如随机数生成器、四舍五入函数和数值表示的限制。 4. **Strings**：介绍字符串的概念，包括字面量字符串和长字符串，讨论了字符串的转换和操作，以及`string`库提供的各种函数。此外，还简要提及了Unicode支持。 5. **Tables**：这是Lua的核心特性之一，它是一种关联数组，可以存储任意类型的数据。章节讨论了表的索引、构造函数、数组、列表和序列的实现，以及遍历表的方法和安全导航。同时，还介绍了`table`库的若干实用功能。 6. **Functions**：讲解了函数的定义和使用，包括多返回值、匿名函数（闭包）以及变量作用域的概念。 7. **Interlude: The Eight-Queen Puzzle**：通过八皇后问题这个经典例子，展示了如何用Lua解决实际问题，帮助读者理解并应用前面学到的知识。 8. **其他章节**：虽然没有给出完整的内容，但可以预期，本书后续会涵盖更多高级话题，如元表、模块、错误处理、垃圾回收机制，以及与C语言的交互等。 "Programming in Lua 4th Edition"是一本详尽的Lua语言指南，它不仅涵盖了基本概念，还深入到高级特性和实践应用，是任何希望掌握Lua编程的人不可或缺的参考资料。

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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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