Programming in Lua

343 Pages·2013·0.921 MB·english

by  Roberto Ierusalimschy

Programming in Lua
Third Edition
Roberto Ierusalimschy
PUC-Rio, Brazil
Lua.org
Rio de Janeiro
Programming in Lua, Third Edition
byRobertoIerusalimschy
ISBN978-85-903798-5-0
Copyright(cid:13)c 2013,2003byRobertoIerusalimschy. Allrightsreserved.
[email protected].
CIP–BibliotecadoDepartamentodeInformática,PUC-Rio
Ierusalimschy,Roberto
I22 ProgramminginLua/RobertoIerusalimschy. –3thed.
–RiodeJaneiro,2013.
xviii,348p. : 25cm.
Includesindex.
ISBN978-85-903798-5-0
1. Lua(Programminglanguage). I.Title.
005.133–dc20
Feisty Duck Digital
Book Distribution
www.feistyduck.com
Contents
Preface xiii
I The Language 1
1 GettingStarted 3
1.1 Chunks 4
1.2 SomeLexicalConventions 5
1.3 GlobalVariables 6
1.4 TheStand-AloneInterpreter 6
Exercises 8
2 TypesandValues 9
2.1 Nil 10
2.2 Booleans 10
2.3 Numbers 10
2.4 Strings 11
2.5 Tables 15
2.6 Functions 18
2.7 UserdataandThreads 18
Exercises 18
3 Expressions 21
3.1 ArithmeticOperators 21
3.2 RelationalOperators 22
3.3 LogicalOperators 23
3.4 Concatenation 23
3.5 TheLengthOperator 24
3.6 Precedence 25
3.7 TableConstructors 26
Exercises 28
4 Statements 29
4.1 Assignment 29
4.2 LocalVariablesandBlocks 30
4.3 ControlStructures 32
4.4 break,return,andgoto 36
Exercises 38
5 Functions 41
5.1 MultipleResults 42
5.2 VariadicFunctions 46
5.3 NamedArguments 48
Exercises 49
6 MoreaboutFunctions 51
6.1 Closures 53
6.2 Non-GlobalFunctions 56
6.3 ProperTailCalls 58
Exercises 59
7 IteratorsandtheGenericfor 61
7.1 IteratorsandClosures 61
7.2 TheSemanticsoftheGenericfor 63
7.3 StatelessIterators 64
7.4 IteratorswithComplexState 66
7.5 TrueIterators 67
Exercises 68
8 Compilation,Execution,andErrors 71
8.1 Compilation 71
8.2 PrecompiledCode 75
8.3 CCode 76
8.4 Errors 77
8.5 ErrorHandlingandExceptions 79
8.6 ErrorMessagesandTracebacks 79
Exercises 81
9 Coroutines 83
9.1 CoroutineBasics 83
9.2 PipesandFilters 86
9.3 CoroutinesasIterators 89
9.4 Non-PreemptiveMultithreading 91
Exercises 95
10 CompleteExamples 97
10.1 TheEight-QueenPuzzle 97
10.2 MostFrequentWords 99
10.3 MarkovChainAlgorithm 101
Exercises 102
II Tables and Objects 105
11 DataStructures 107
11.1 Arrays 107
11.2 MatricesandMulti-DimensionalArrays 108
11.3 LinkedLists 110
11.4 QueuesandDoubleQueues 110
11.5 SetsandBags 111
11.6 StringBuffers 113
11.7 Graphs 114
Exercises 116
12 DataFilesandPersistence 117
12.1 DataFiles 117
12.2 Serialization 119
Exercises 125
13 MetatablesandMetamethods 127
13.1 ArithmeticMetamethods 128
13.2 RelationalMetamethods 131
13.3 Library-DefinedMetamethods 132
13.4 Table-AccessMetamethods 133
Exercises 138
14 TheEnvironment 139
14.1 GlobalVariableswithDynamicNames 139
14.2 Global-VariableDeclarations 141
14.3 Non-GlobalEnvironments 142
14.4 Using_ENV 144
14.5 _ENVandload 147
Exercises 148
15 ModulesandPackages 151
15.1 TherequireFunction 153
15.2 TheBasicApproachforWritingModulesinLua 156
15.3 UsingEnvironments 158
15.4 SubmodulesandPackages 159
Exercises 161
16 Object-OrientedProgramming 163
16.1 Classes 165
16.2 Inheritance 166
16.3 MultipleInheritance 168
16.4 Privacy 170
16.5 TheSingle-MethodApproach 172
Exercises 173
17 WeakTablesandFinalizers 175
17.1 WeakTables 175
17.2 MemoizeFunctions 177
17.3 ObjectAttributes 179
17.4 RevisitingTableswithDefaultValues 179
17.5 EphemeronTables 180
17.6 Finalizers 181
Exercises 185
III The Standard Libraries 187
18 TheMathematicalLibrary 189
Exercises 190
19 TheBitwiseLibrary 191
Exercises 194
20 TheTableLibrary 195
20.1 InsertandRemove 195
20.2 Sort 196
20.3 Concatenation 197
Exercises 198
21 TheStringLibrary 199
21.1 BasicStringFunctions 199
21.2 Pattern-MatchingFunctions 201
21.3 Patterns 204
21.4 Captures 208
21.5 Replacements 209
21.6 TricksoftheTrade 213
21.7 Unicode 216
Exercises 218
22 TheI/OLibrary 221
22.1 TheSimpleI/OModel 221
22.2 TheCompleteI/OModel 224
22.3 OtherOperationsonFiles 228
Exercises 229
23 TheOperatingSystemLibrary 231
23.1 DateandTime 231
23.2 OtherSystemCalls 233
Exercises 235
24 TheDebugLibrary 237
24.1 IntrospectiveFacilities 237
24.2 Hooks 242
24.3 Profiles 243
Exercises 245
IV The C API 247
25 AnOverviewoftheCAPI 249
25.1 AFirstExample 250
25.2 TheStack 253
25.3 ErrorHandlingwiththeCAPI 258
Exercises 260
26 ExtendingYourApplication 261
26.1 TheBasics 261
26.2 TableManipulation 263
26.3 CallingLuaFunctions 267
26.4 AGenericCallFunction 269
Exercises 270
27 CallingCfromLua 273
27.1 CFunctions 273
27.2 Continuations 275
27.3 CModules 278
Exercises 280
28 TechniquesforWritingCFunctions 281
28.1 ArrayManipulation 281
28.2 StringManipulation 283
28.3 StoringStateinCFunctions 286
Exercises 292
29 User-DefinedTypesinC 293
29.1 Userdata 294
29.2 Metatables 296
29.3 Object-OrientedAccess 299
29.4 ArrayAccess 300
29.5 LightUserdata 301
Exercises 302
30 ManagingResources 305
30.1 ADirectoryIterator 305
30.2 AnXMLParser 307
Exercises 316
31 ThreadsandStates 319
31.1 MultipleThreads 319
31.2 LuaStates 323
Exercises 331
32 MemoryManagement 333
32.1 TheAllocationFunction 333
32.2 TheGarbageCollector 335
Exercises 338
Index 339
Preface
When Waldemar, Luiz, and I started the development of Lua, back in 1993, we
could hardly imagine that it would spread as it did. Started as an in-house
languagefortwospecificprojects,currentlyLuaiswidelyusedinallareasthat
canbenefitfromasimple,extensible,portable,andefficientscriptinglanguage,
suchasembeddedsystems,mobiledevices,and,ofcourse,games.
WedesignedLua,fromthebeginning,tobeintegratedwithsoftwarewritten
in C/C++ and other conventional languages. This integration brings many
benefits. Lua is a tiny and simple language, partly because it does not try to
do what C is already good for, such as sheer performance, low-level operations,
and interface with third-party software. Lua relies on C for these tasks. What
Lua does offer is what C is not good for: a good distance from the hardware,
dynamic structures, no redundancies, and ease of testing and debugging. For
these goals, Lua has a safe environment, automatic memory management, and
goodfacilitiesforhandlingstringsandotherkindsofdatawithdynamicsize.
PartofthepowerofLuacomesfromitslibraries. Thisisnotbychance. After
all, one of the main strengths of Lua is its extensibility. Many features con-
tributetothisstrength. Dynamictypingallowsagreatdegreeofpolymorphism.
Automaticmemorymanagementsimplifiesinterfaces, becausethereisnoneed
to decide who is responsible for allocating and deallocating memory, or how to
handleoverflows. Higher-orderfunctionsandanonymousfunctionsallowahigh
degreeofparameterization,makingfunctionsmoreversatile.
Morethananextensiblelanguage,Luaisalsoagluelanguage. Luasupports
a component-based approach to software development, where we create an ap-
plication by gluing together existing high-level components. These components
arewritteninacompiled,staticallytypedlanguage,suchasCorC++;Luaisthe
gluethatweusetocomposeandconnectthesecomponents. Usually,thecompo-
nents (or objects) represent more concrete, low-level concepts (such as widgets
and data structures) that are not subject to many changes during program de-
velopment, and that take the bulk of the CPU time of the final program. Lua
gives the final shape of the application, which will probably change a lot dur-
ing the life cycle of the product. However, unlike other glue technologies, Lua
is a full-fledged language as well. Therefore, we can use Lua not only to glue
xiv Preface
components, but also to adapt and reshape them, and to create completely new
components.
Of course, Lua is not the only scripting language around. There are other
languages that you can use for more or less the same purposes. Nevertheless,
Lua offers a set of features that makes it your best choice for many tasks and
givesitauniqueprofile:
Extensibility: Lua’sextensibilityissoremarkablethatmanypeopleregardLua
notasalanguage,butasakitforbuildingdomain-specificlanguages. We
designed Lua from scratch to be extended, both through Lua code and
through external C code. As a proof of concept, Lua implements most of
its own basic functionality through external libraries. It is really easy to
interfaceLuawithC/C++,andLuahasbeenusedintegratedwithseveral
other languages as well, such as Fortran, Java, Smalltalk, Ada, C#, and
evenwithotherscriptinglanguages,suchasPerlandPython.
Simplicity: Lua is a simple and small language. It has few (but powerful)
concepts. This simplicity makes Lua easy to learn and contributes to its
small size. Its complete distribution (source code, manual, plus binaries
forsomeplatforms)fitscomfortablyinafloppydisk.
Efficiency: Luahasaquiteefficientimplementation. Independentbenchmarks
show Lua as one of the fastest languages in the realm of scripting lan-
guages.
Portability: Whenwetalkaboutportability,wearetalkingaboutrunningLua
on all platforms we have ever heard about: all flavors of UNIX and Win-
dows,PlayStation,Xbox,MacOSXandiOS,Android,KindleFire,NOOK,
Haiku,QUALCOMMBrew,IBMmainframes,RISCOS,SymbianOS,Rab-
bitprocessors,RaspberryPi,Arduino,andmanymore. Thesourcecodefor
eachoftheseplatformsisvirtuallythesame. Luadoesnotuseconditional
compilation to adapt its code to different machines; instead, it sticks to
the standard ANSI (ISO) C. This way, you do not usually need to adapt it
to a new environment: if you have an ANSI C compiler, you just have to
compileLua,outofthebox.
Audience
Lua users typically fall into three broad groups: those that use Lua already
embeddedinanapplicationprogram,thosethatuseLuastandalone,andthose
thatuseLuaandCtogether.
Many people use Lua embedded in an application program, such as Adobe
Lightroom,Nmap,orWorldofWarcraft. TheseapplicationsusetheLua–CAPI
to register new functions, to create new types, and to change the behavior of
some language operations, configuring Lua for their specific domains. Fre-
quently, the users of such applications do not even know that Lua is an inde-
pendent language adapted for a particular domain. For instance, many devel-
opers of plug-ins for Lightroom do not know about other uses of the language;