Lua编程语言第四版精华指南

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"Programming.in.Lua第四版.pdf" 本书是关于编程语言Lua的第四版，作者是Roberto Ierusalimschy。这本书旨在帮助读者快速掌握Lua编程，虽然英文版可能需要一定的阅读耐心。该书涵盖了Lua的基础知识，包括变量、类型、数值、字符串、表和函数等核心概念。在“Getting Started”章节中，介绍了如何开始使用Lua，讲解了块（Chunks）的概念，这是Lua程序的基本结构单位。同时，书中也提到了一些词法约定，如变量的声明和使用。全局变量在Lua中占有重要地位，因为它们默认是全局的，但同时也存在一些潜在的问题需要注意。 “Numbers”章节深入探讨了Lua中的数值类型，包括数值表示（Numerals）、算术运算符、关系运算符以及数学库，如随机数生成器、舍入函数以及数值表示的限制。作者还讨论了Lua在处理整数上的历史变化。在“Strings”部分，作者解释了Lua中的字符串表示，包括字面量字符串和长字符串，以及字符串与数字之间的转换。此外，还介绍了字符串库的一些常用功能，如字符串操作函数。书中还提到了Unicode支持，这对于处理多语言文本非常重要。 “Tables”章节是Lua的一大特色，它是一种灵活的数据结构，可以作为数组、列表或序列使用。这里详细解释了表的索引、构造器以及数组的实现。表的遍历方法和安全导航技巧也进行了阐述，同时提到了Lua的表库，提供了许多实用的表操作函数。 “Functions”章节则介绍了Lua中的函数，包括函数定义、参数传递和返回值。Lua支持多返回值，这在其他语言中并不常见，这一特性使得函数更加灵活。此外，书中还涉及了闭包和匿名函数的概念。这只是《Programming in Lua》第四版的一部分内容概述，全书详细地介绍了Lua的所有主要特性和用法，对于想要深入理解或学习Lua的读者来说，是一份宝贵的资源。通过阅读本书，读者不仅可以了解Lua的基础知识，还能学习到高级特性和最佳实践，从而在实际项目中更有效地利用Lua。

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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