Programming in Lua, Fourth Edition

Programming in Lua, Fourth Edition

Roberto Ierusalimschy Copyright ? 2016, 2003 Roberto Ierusalimschy

Feisty Duck Digital Book Distribution

Licensed for the exclusive use of: Eric Taylor

Contents

About the Book ................................................................................................................. ix I. The Basics ...................................................................................................................... 1

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 Generic for .............................................................................................. 60 break, return, and goto ..................................................................................... 61 II. Real Programming ......................................................................................................... 65 9. Closures ............................................................................................................... 68 Functions as First-Class Values ............................................................................ 68 Non-Global Functions ........................................................................................ 69 Lexical Scoping ................................................................................................ 71 A Taste of Functional Programming ..................................................................... 74 10. Pattern Matching .................................................................................................. 77 The Pattern-Matching Functions ........................................................................... 77 The function string.find ...................................................................... 77 The function string.match .................................................................... 77 The function string.gsub ...................................................................... 78 The function string.gmatch .................................................................. 78 Patterns ............................................................................................................ 78 Captures ........................................................................................................... 82 Replacements .................................................................................................... 83 URL encoding .......................................................................................... 84 Tab expansion ........................................................................................... 86 Tricks of the Trade ............................................................................................ 86 11. Interlude: Most Frequent Words ............................................................................. 90 12. Date and Time ..................................................................................................... 92 The Function os.time ..................................................................................... 92 The Function os.date ..................................................................................... 93 Date?Time Manipulation .................................................................................... 95 13. Bits and Bytes ..................................................................................................... 97 Bitwise Operators .............................................................................................. 97 Unsigned Integers .............................................................................................. 97 Packing and Unpacking Binary Data ..................................................................... 99 Binary files ..................................................................................................... 101 14. Data Structures ................................................................................................... 104 Arrays ............................................................................................................ 104 Matrices and Multi-Dimensional Arrays ............................................................... 105 Linked Lists .................................................................................................... 107 Queues and Double-Ended Queues ..................................................................... 107 Reverse Tables ................................................................................................ 108 Sets and Bags ................................................................................................. 109 String Buffers .................................................................................................. 110 Graphs ........................................................................................................... 111 15. Data Files and Serialization .................................................................................. 114 Data Files ....................................................................................................... 114 Serialization .................................................................................................... 116 Saving tables without cycles ...................................................................... 118 Saving tables with cycles .......................................................................... 119 16. Compilation, Execution, and Errors ....................................................................... 122 Compilation .................................................................................................... 122 Precompiled Code ............................................................................................ 125 Errors ............................................................................................................. 126 Error Handling and Exceptions .......................................................................... 127 Error Messages and Tracebacks .......................................................................... 128 17. Modules and Packages ........................................................................................ 131 The Function require .................................................................................... 132

Renaming a module ................................................................................. 133 Path searching ......................................................................................... 133 Searchers ................................................................................................ 135 The Basic Approach for Writing Modules in Lua .................................................. 135 Submodules and Packages ................................................................................. 137 III. Lua-isms ................................................................................................................... 139 18. Iterators and the Generic for ................................................................................ 142 Iterators and Closures ....................................................................................... 142 The Semantics of the Generic for ....................................................................... 143 Stateless Iterators ............................................................................................. 145 Traversing Tables in Order ................................................................................ 146 True Iterators .................................................................................................. 147 19. Interlude: Markov Chain Algorithm ....................................................................... 149 20. Metatables and Metamethods ................................................................................ 152 Arithmetic Metamethods ................................................................................... 152 Relational Metamethods .................................................................................... 155 Library-Defined Metamethods ............................................................................ 155 Table-Access Metamethods ............................................................................... 156 The __index metamethod ....................................................................... 156 The __newindex metamethod ................................................................. 157 Tables with default values ......................................................................... 158 Tracking table accesses ............................................................................. 159 Read-only tables ...................................................................................... 160 21. Object-Oriented Programming .............................................................................. 162 Classes ........................................................................................................... 163 Inheritance ...................................................................................................... 165 Multiple Inheritance ......................................................................................... 166 Privacy ........................................................................................................... 168 The Single-Method Approach ............................................................................ 170 Dual Representation ......................................................................................... 170 22. The Environment ................................................................................................ 173 Global Variables with Dynamic Names ............................................................... 173 Global-Variable Declarations ............................................................................. 174 Non-Global Environments ................................................................................. 176 Using _ENV .................................................................................................... 177 Environments and Modules ............................................................................... 180 _ENV and load .............................................................................................. 181 23. Garbage ............................................................................................................ 183 Weak Tables ................................................................................................... 183 Memorize Functions ......................................................................................... 184 Object Attributes ............................................................................................. 185 Revisiting Tables with Default Values ................................................................. 186 Ephemeron Tables ........................................................................................... 187 Finalizers ........................................................................................................ 188 The Garbage Collector ...................................................................................... 190 Controlling the Pace of Collection ...................................................................... 191 24. Coroutines ......................................................................................................... 194 Coroutine Basics .............................................................................................. 194 Who Is the Boss? ............................................................................................ 196 Coroutines as Iterators ...................................................................................... 198 Event-Driven Programming ............................................................................... 200 25. Reflection .......................................................................................................... 205 Introspective Facilities ...................................................................................... 205 Accessing local variables .......................................................................... 207

Accessing non-local variables .................................................................... 208 Accessing other coroutines ........................................................................ 209 Hooks ............................................................................................................ 210 Profiles .......................................................................................................... 211 Sandboxing ..................................................................................................... 212 26. Interlude: Multithreading with Coroutines ............................................................... 217 IV. The C API ................................................................................................................ 221 27. An Overview of the C API .................................................................................. 223 A First Example .............................................................................................. 223 The Stack ....................................................................................................... 225 Pushing elements ..................................................................................... 226 Querying elements ................................................................................... 227 Other stack operations .............................................................................. 229 Error Handling with the C API .......................................................................... 231 Error handling in application code .............................................................. 232 Error handling in library code .................................................................... 232 Memory Allocation .......................................................................................... 233 28. Extending Your Application ................................................................................. 236 The Basics ...................................................................................................... 236 Table Manipulation .......................................................................................... 237 Some short cuts ....................................................................................... 240 Calling Lua Functions ...................................................................................... 241 A Generic Call Function ................................................................................... 242 29. Calling C from Lua ............................................................................................ 247 C Functions .................................................................................................... 247 Continuations .................................................................................................. 249 C Modules ...................................................................................................... 251 30. Techniques for Writing C Functions ...................................................................... 254 Array Manipulation .......................................................................................... 254 String Manipulation .......................................................................................... 255 Storing State in C Functions .............................................................................. 258 The registry ............................................................................................ 258 Upvalues ................................................................................................ 260 Shared upvalues ....................................................................................... 263 31. User-Defined Types in C ..................................................................................... 265 Userdata ......................................................................................................... 265 Metatables ...................................................................................................... 268 Object-Oriented Access ..................................................................................... 270 Array Access .................................................................................................. 271 Light Userdata ................................................................................................. 272 32. Managing Resources ........................................................................................... 274 A Directory Iterator .......................................................................................... 274 An XML Parser ............................................................................................... 277 33. Threads and States .............................................................................................. 286 Multiple Threads ............................................................................................. 286 Lua States ...................................................................................................... 289

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