DOCSLIB.ORG

Programming in Lua, Second Edition by Roberto Ierusalimschy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Programming in Lua, Second Edition by Roberto Ierusalimschy Programming ROBERTO IERUSALIMSCHY in Lua 2nd edition Lua.org Last update: Wed Jan 13 12:07:33 UTC 2010 Programming in Lua Property of Ian Bloss <[email protected]> Property of Ian Bloss <[email protected]> Programming in Lua Second Edition Roberto Ierusalimschy PUC-Rio, Brazil Lua.org Rio de Janeiro Property of Ian Bloss <[email protected]> Programming in Lua, Second Edition by Roberto Ierusalimschy ISBN 85-903798-2-5 Copyright c 2006, 2003 by Roberto Ierusalimschy. All rights reserved. The author can be contacted at [email protected]. Book cover and illustrations by Dimaquina. Lua logo design by Alexandre Nako. Typesetting by the author using LATEX. Although the author used his best efforts preparing this book, he assumes no responsibility for errors or omissions, or for any damage that may result from the use of the information presented here. All product names mentioned in this book are trademarks of their respective owners. CIP – Biblioteca do Departamento de Informatica,´ PUC-Rio Ierusalimschy, Roberto I22 Programming in Lua / Roberto Ierusalimschy. – 2nd ed. – Rio de Janeiro, 2006. xviii, 308 p. : 25 cm. Includes index. ISBN 85-903798-2-5 1. Lua (Programming language). I. Title. 005.133 – dc20 Property of Ian Bloss <[email protected]> to Ida, Noemi, and Ana Lucia Property of Ian Bloss <[email protected]> Property of Ian Bloss <[email protected]> Contents Preface xiii I The Language 1 1 Getting Started 3 1.1 Chunks 4 1.2 Some Lexical Conventions 5 1.3 Global Variables 6 1.4 The Stand-Alone Interpreter 7 2 Types and Values 9 2.1 Nil 10 2.2 Booleans 10 2.3 Numbers 10 2.4 Strings 11 2.5 Tables 13 2.6 Functions 17 2.7 Userdata and Threads 17 3 Expressions 19 3.1 Arithmetic Operators 19 3.2 Relational Operators 20 3.3 Logical Operators 21 3.4 Concatenation 22 3.5 Precedence 22 3.6 Table Constructors 22 vii Property of Ian Bloss <[email protected]> viii Contents 4 Statements 27 4.1 Assignment 27 4.2 Local Variables and Blocks 28 4.3 Control Structures 30 4.4 break and return 34 5 Functions 35 5.1 Multiple Results 36 5.2 Variable Number of Arguments 39 5.3 Named Arguments 42 6 More About Functions 45 6.1 Closures 47 6.2 Non-Global Functions 50 6.3 Proper Tail Calls 52 7 Iterators and the Generic for 55 7.1 Iterators and Closures 55 7.2 The Semantics of the Generic for 57 7.3 Stateless Iterators 58 7.4 Iterators with Complex State 60 7.5 True Iterators 61 8 Compilation, Execution, and Errors 63 8.1 Compilation 63 8.2 C Code 67 8.3 Errors 67 8.4 Error Handling and Exceptions 69 8.5 Error Messages and Tracebacks 70 9 Coroutines 73 9.1 Coroutine Basics 73 9.2 Pipes and Filters 76 9.3 Coroutines as Iterators 79 9.4 Non-Preemptive Multithreading 81 10 Complete Examples 87 10.1 Data Description 87 10.2 Markov Chain Algorithm 91 II Tables and Objects 95 11 Data Structures 97 11.1 Arrays 97 Property of Ian Bloss <[email protected]> ix 11.2 Matrices and Multi-Dimensional Arrays 98 11.3 Linked Lists 100 11.4 Queues and Double Queues 100 11.5 Sets and Bags 101 11.6 String Buffers 103 11.7 Graphs 104 12 Data Files and Persistence 107 12.1 Data Files 107 12.2 Serialization 109 13 Metatables and Metamethods 117 13.1 Arithmetic Metamethods 118 13.2 Relational Metamethods 120 13.3 Library-Defined Metamethods 122 13.4 Table-Access Metamethods 122 14 The Environment 129 14.1 Global Variables with Dynamic Names 129 14.2 Global-Variable Declarations 131 14.3 Non-Global Environments 132 15 Modules and Packages 137 15.1 The require Function 138 15.2 The Basic Approach for Writing Modules 141 15.3 Using Environments 143 15.4 The module Function 144 15.5 Submodules and Packages 145 16 Object-Oriented Programming 149 16.1 Classes 151 16.2 Inheritance 152 16.3 Multiple Inheritance 154 16.4 Privacy 156 16.5 The Single-Method Approach 158 17 Weak Tables 161 17.1 Memoize Functions 163 17.2 Object Attributes 164 17.3 Revisiting Tables with Default Values 165 III The Standard Libraries 167 18 The Mathematical Library 169 Property of Ian Bloss <[email protected]> x Contents 19 The Table Library 171 19.1 Insert and Remove 171 19.2 Sort 172 19.3 Concatenation 173 20 The String Library 175 20.1 Basic String Functions 175 20.2 Pattern-Matching Functions 177 20.3 Patterns 180 20.4 Captures 183 20.5 Replacements 185 20.6 Tricks of the Trade 189 21 The I/O Library 193 21.1 The Simple I/O Model 193 21.2 The Complete I/O Model 196 21.3 Other Operations on Files 199 22 The Operating System Library 201 22.1 Date and Time 201 22.2 Other System Calls 203 23 The Debug Library 205 23.1 Introspective Facilities 205 23.2 Hooks 210 23.3 Profiles 211 IV The C API 215 24 An Overview of the C API 217 24.1 A First Example 218 24.2 The Stack 221 24.3 Error Handling with the C API 225 25 Extending Your Application 229 25.1 The Basics 229 25.2 Table Manipulation 231 25.3 Calling Lua Functions 235 25.4 A Generic Call Function 236 26 Calling C from Lua 241 26.1 C Functions 241 26.2 C Modules 244 Property of Ian Bloss <[email protected]> xi 27 Techniques for Writing C Functions 247 27.1 Array Manipulation 247 27.2 String Manipulation 249 27.3 Storing State in C Functions 251 28 User-Defined Types in C 259 28.1 Userdata 260 28.2 Metatables 262 28.3 Object-Oriented Access 265 28.4 Array Access 267 28.5 Light Userdata 268 29 Managing Resources 269 29.1 A Directory Iterator 269 29.2 An XML Parser 271 30 Threads and States 281 30.1 Multiple Threads 281 30.2 Lua States 285 31 Memory Management 293 31.1 The Allocation Function 293 31.2 The Garbage Collector 295 Index 299 Property of Ian Bloss <[email protected]> Property of Ian Bloss <[email protected]> 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 language for two specific projects, currently Lua is widely used in all areas that can benefit from a simple, extensible, portable, and efficient scripting language, such as embedded systems, mobile devices, web servers, and, of course, games. We designed Lua, from the beginning, to be integrated with software written in 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, ease of testing and debugging. For this, Lua has a safe environment, automatic memory management, and good facilities for handling strings and other kinds of data with dynamic size. A great part of the power of Lua comes from its libraries. This is not by chance. After all, one of the main strengths of Lua is its extensibility. Many fea- tures contribute to this strength. Dynamic typing allows a great degree of poly- morphism. Automatic memory management simplifies interfaces, because there is no need to decide who is responsible for allocating and deallocating memory, or how to handle overflows. Higher-order functions and anonymous functions allow a high degree of parameterization, making functions more versatile. More than an extensible language, Lua is also a glue language. Lua sup- ports a component-based approach to software development, where we create an application by gluing together existing high-level components. These com- ponents are written in a compiled, statically typed language, such as C or C++; Lua is the glue that we use to compose and connect these components. Usually, the components (or objects) represent more concrete, low-level concepts (such as widgets and data structures) that are not subject to many changes during pro- gram development, 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 during 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 xiii Property of Ian Bloss <[email protected]> xiv Preface glue components, but also to adapt and reshape them, and to create whole 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. But Lua offers a set of features that makes it your best choice for many tasks and gives it a unique profile: Extensibility: Lua's extensibility is so remarkable that many people regard Lua not as a language, but as a kit for building domain-specific languages. Lua has been designed 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.
Load more

Recommended publications
  • Ercatons and Organic Programming: Say Good-Bye to Planned Economy
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Dagstuhl Research Online Publication Server Ercatons and Organic Programming: Say Good-Bye to Planned Economy Oliver Imbusch, Falk Langhammer and Guido von Walter Living Pages Research GmbH Kolosseumstrasse 1a, 80469 Munich, Germany {flabes|falk|guido}@livis.com ABSTRACT 1. Motivation Organic programming (OP) is our proposed and already We are going to present an alternative way to develop soft- emerging programming model which overcomes some of ware. We followed this idea starting from some general the limitations of current practice in software development observations all the way down to a reference implementa- in general and of object-oriented programming (OOP) in tion which was then used in projects of sufficient size. This particular. Ercatons provide an implementation of the makes us trust into the initial idea to the point that we may model. In some respects, OP is less than a (new) program- now be obsessed by it. Let us start by sharing some of the ming language, in others, it is more. An “ercato machine” general observations. implements the ideas discussed and has been used to vali- We start with this trivial anecdote. date the concepts described here. “One morning, we noticed some workers tile our office's Organic programming is centered around the concept of a backyard. The day before, piles of square tiles had been true “Thing”. A thing in an executing software system is delivered and the workers now seemed to make good prog- bound to behave the way an autonomous object does in our ress covering the backyard's middle section.
    [Show full text]
  • Dynamic, Instance-Based, Object-Oriented Programming in Max/Msp Using Open Sound Control Message Delegation
    Proceedings of the International Computer Music Conference 2011, University of Huddersfield, UK, 31 July - 5 August 2011 DYNAMIC, INSTANCE-BASED, OBJECT-ORIENTED PROGRAMMING IN MAX/MSP USING OPEN SOUND CONTROL MESSAGE DELEGATION Adrian Freed John MacCallum Andrew Schmeder CNMAT CNMAT CNMAT Dept. of Music Dept. of Music Dept. of Music UC Berkeley, CA 94709 UC Berkeley, CA 94709 UC Berkeley, CA 94709 [email protected] [email protected] [email protected] ABSTRACT oriented programming in Max–presumably because of the hegemony of statically-typed class-based object- A new media programming style is introduced that oriented programming invented in Simula (1962) and brings efficient run-time polymorphism, functional and still active in Objective-C, C++ and Java. instance-based object-oriented programming to Max/MSP and related visual dataflow languages. In 2007 the first author developed a suite of Max/MSP Examples are presented to illustrate new, unusual and patches, called “o.” (pronounced “Oh dot”). These were effective applications of the approach of using OSC specifically designed to exploit generic programming messages for object representations and data flow for (pioneered in Ada in 1980) to simplify and teach gesture method delegation. signal processing in physical computing contexts. This early prototype explored the use of OSC (Sections 2-3 1. INTRODUCTION of this paper), ad-hoc polymorphism and delegation Open Sound Control (OSC) was originally designed as a (Sections 4 and 6) for dynamic class-less object- message-passing format to facilitate exchange of control orientated programming (OOP) based on his experience parameters between programs on different computers developing music programs in prototype-based OOP across a network.
    [Show full text]
  • The Self-4.0 User Interface: Manifesting a System-Wide Vision of Concreteness, Uniformity, and Flexibility
    The Self-4.0 User Interface: Manifesting a System-wide Vision of Concreteness, Uniformity, and Flexibility Randall B. Smith, John Maloney†, and David Ungar Sun Microsystems Laboratories 2550 Casey Ave. MTV29-116 Mountain View, CA 94043 [email protected], [email protected], [email protected] Abstract ming systems seem pretty awkward and abstruse by comparison. Manipulating programs is hard, while manipulating Of course it would be a difficult and dubious objects in the physical world is often easy. Several attributes of the physical world help make it compre- effort to literally replicate the physical world in the hensible and manipulable: concreteness, uniformity, computer. But embodying key elements of our physi- and flexibility. The Self programming system cal reality might bring benefits to the computing attempts to apply these attributes to the world within experience. The rise of object-oriented programming the computer. The semantics of the language, the may be viewed as the outcome of an effort to allow efficiency and fidelity of its implementation, and the computers to more directly model physical systems. architecture of its user interface conspire to make the experience of constructing programs in Self immedi- However, even object-oriented programming sys- ate and tangible. We describe the mechanisms used tems don’t really give you anything like that real- to achieve this goal, and illustrate those mechanisms world sense of obvious straightforwardness, that within the context of an extended programming task. sense of immediacy. We believe something more can be found by reexamining the essence of physical sys- tems. I. Introduction Three important characteristics of physical reality that are not truly present in most program- There is a satisfying directness in working ming systems, even object-oriented ones, are con- with physical objects.
    [Show full text]
  • Comparative Programming Languages CM20253
    We have briefly covered many aspects of language design And there are many more factors we could talk about in making choices of language The End There are many languages out there, both general purpose and specialist And there are many more factors we could talk about in making choices of language The End There are many languages out there, both general purpose and specialist We have briefly covered many aspects of language design The End There are many languages out there, both general purpose and specialist We have briefly covered many aspects of language design And there are many more factors we could talk about in making choices of language Often a single project can use several languages, each suited to its part of the project And then the interopability of languages becomes important For example, can you easily join together code written in Java and C? The End Or languages And then the interopability of languages becomes important For example, can you easily join together code written in Java and C? The End Or languages Often a single project can use several languages, each suited to its part of the project For example, can you easily join together code written in Java and C? The End Or languages Often a single project can use several languages, each suited to its part of the project And then the interopability of languages becomes important The End Or languages Often a single project can use several languages, each suited to its part of the project And then the interopability of languages becomes important For example, can you easily
    [Show full text]
  • The Evolution of Lua
    The Evolution of Lua Roberto Ierusalimschy Luiz Henrique de Figueiredo Waldemar Celes Department of Computer Science, IMPA–Instituto Nacional de Department of Computer Science, PUC-Rio, Rio de Janeiro, Brazil Matematica´ Pura e Aplicada, Brazil PUC-Rio, Rio de Janeiro, Brazil [email protected] [email protected] [email protected] Abstract ing languages offer associative arrays, in no other language We report on the birth and evolution of Lua and discuss how do associative arrays play such a central role. Lua tables it moved from a simple configuration language to a versatile, provide simple and efficient implementations for modules, widely used language that supports extensible semantics, prototype-based objects, class-based objects, records, arrays, anonymous functions, full lexical scoping, proper tail calls, sets, bags, lists, and many other data structures [28]. and coroutines. In this paper, we report on the birth and evolution of Lua. We discuss how Lua moved from a simple configuration Categories and Subject Descriptors K.2 [HISTORY OF language to a powerful (but still simple) language that sup- COMPUTING]: Software; D.3 [PROGRAMMING LAN- ports extensible semantics, anonymous functions, full lexical GUAGES] scoping, proper tail calls, and coroutines. In §2 we give an overview of the main concepts in Lua, which we use in the 1. Introduction other sections to discuss how Lua has evolved. In §3 we re- late the prehistory of Lua, that is, the setting that led to its Lua is a scripting language born in 1993 at PUC-Rio, the creation. In §4 we relate how Lua was born, what its original Pontifical Catholic University of Rio de Janeiro in Brazil.
    [Show full text]
  • 8. Objects and Prototypes
    8. Objects and Prototypes Oscar Nierstrasz Based on material by Adrian Lienhard All examples can be found in the usual git repo, [email protected]:lectures-pl-examples as well as online: http://scg.unibe.ch/download/lectures/pl-examples/JavaScript/ Roadmap > Class- vs. prototype-based languages > Objects, properties and methods > Delegation > Constructors > Closures > Snakes and Ladders with prototypes > The Good, the Bad and the Ugly 2 References > JavaScript: The Definitive Guide, D. Flanagan, O’Reilly, 5th edition > JavaScript: The Good Parts, D. Crockford, O’Reilly > JavaScript Guide & Reference, Mozilla Developer Center, http:// developer.mozilla.org/en/docs/JavaScript > Using Prototypical Objects to Implement Shared Behavior in Object Oriented Systems, H. Lieberman, OOPSLA’86 > ECMAScript Language Specification — 5th edition, http://www.ecma- international.org/publications/standards/Ecma-262.htm > ECMAScript 6 features —http://es6-features.org/#Constants 3 Roadmap > Class- vs. prototype-based languages > Objects, properties and methods > Delegation > Constructors > Closures > Snakes and Ladders with prototypes > The Good, the Bad and the Ugly 4 Class-based vs. Prototype-based languages Class-based: Prototype-based: > Classes share methods and > No classes, only objects define common properties > Objects define their own > Inheritance along class chain properties and methods > Instances have exactly the > Objects delegate to their properties and behavior prototype(s) defined by their class > Any object can be the prototype > Structure typically cannot be of another object changed at runtime Prototype-based languages unify objects and classes 6 In class-based languages, classes may (e.g., in Smalltalk) or may not be (e.g., in Java) be first-class objects.
    [Show full text]
  • Javascript: the First 20 Years
    JavaScript: The First 20 Years ALLEN WIRFS-BROCK, Wirfs-Brock Associates, Inc., USA BRENDAN EICH, Brave Software, Inc., USA Shepherds: Sukyoung Ryu, KAIST, South Korea Richard P. Gabriel: poet, writer, computer scientist How a sidekick scripting language for Java, created at Netscape in a ten-day hack, ships first as a de facto Web standard and eventually becomes the world’s most widely used programming language. This paper tells the story of the creation, design, evolution, and standardization of the JavaScript language over the period of 1995–2015. But the story is not only about the technical details of the language. It is also the story of how people and organizations competed and collaborated to shape the JavaScript language which dominates the Web of 2020. CCS Concepts: • General and reference ! Computing standards, RFCs and guidelines; • Information systems ! World Wide Web; • Social and professional topics ! History of computing; History of programming languages; • Software and its engineering ! General programming languages; Scripting languages. Additional Key Words and Phrases: JavaScript, ECMAScript, Standards, Web browsers, Browser game theory, History of programming languages ACM Reference Format: Allen Wirfs-Brock and Brendan Eich. 2020. JavaScript: The First 20 Years. Proc. ACM Program. Lang. 4, HOPL (June 2020), 190 pages. https://doi.org/10.1145/3386327 1 INTRODUCTION In 2020, the World Wide Web is ubiquitous with over a billion websites accessible from billions of Web-connected devices. Each of those devices runs a Web browser or similar program which is able to process and display pages from those sites. The majority of those pages embed or load source code written in the JavaScript programming language.
    [Show full text]
  • The Newton Application Architecture
    In Proceedings of the 39th IEEE Computer Society International Conference, pp. 156–161, San Francisco, 1994. Copyright 1994 IEEE The Newton Application Architecture Walter R. Smith Apple Computer, Inc. Cupertino, California 95014 [email protected] Abstract tion behavior. Finally, the object store is used by applica- tions to store and retrieve objects. The application architecture of Newton, a technology The other parts of the architecture are more indepen- for supporting Personal Digital Assistants (PDAs), is dent. There is a flexible and extensible communications described. It combines a dynamic, object-oriented lan- system. The recognition architecture, also extensible, guage called NewtonScript with a hierarchical view sys- interprets user input. Add-on software is delivered in the tem and a persistent object store. It also contains form of packages that combine multiple pieces of soft- extensible subsystems for communications and user-input ware into a single unit. recognition. In addition to PDA devices, the portable Most of the implementation is highly portable. We implementation has been used to build supporting tools have re-used parts of the architecture to construct a set of for desktop machines. tools that run on computers using the Microsoft Windows and Macintosh operating environments. These tools are used by end users, programmers, and content developers. 1. Introduction 3. Object system Newton technology was designed to support a new type of computing device, the “personal digital assistant”. The object system is used by other parts of the system PDAs are intended to help people capture, organize, and to represent data. The data model is similar to that found communicate information more effectively.
    [Show full text]
  • Proto: an R Package for Prototype Programming
    proto: An R Package for Prototype Programming Louis Kates Thomas Petzoldt GKX Associates Inc. Technische Universit¨at Dresden Abstract proto is an R package which facilitates a style of programming known as prototype programming. Prototype programming is a type of object oriented programming in which there are no classes. proto is simple yet retains the object oriented features of delegation (the prototype counterpart to inheritance) and object oriented dispatch. proto can be used to organize the concrete data and procedures in statistical studies and other appli- cations without the necessity of defining classes while still providing convenient access to an object oriented style of programming. Furthermore, it can be used in a class-based style as well so that incremental design can begin with defining the concrete objects and later transition to abstract classes, once the general case is understood, without having to change to object-oriented frameworks. The key goals of the package are to integrate into R while providing nothing more than a thin layer on top of it. Keywords: prototype programming, delegation, inheritance, clone, object orientated, S3, R. 1. Introduction 1.1. Object Oriented Programming in R The R system for statistical computing (R Development Core Team 2005, http://www. R-project.org/) ships with two systems for object oriented programming referred to as S3 and S4. With the increased interest in object oriented programming within R over the last years additional object oriented programming packages emerged. These include the R.oo package (Bengtsson 2003) and the OOP package (Chambers and Lang 2001, http: //www.omegahat.net/OOP/).
    [Show full text]
  • Applying Prototype-Based Programming Techniques for the Organization of Mobile Systems
    Vrije Universiteit Brussel Faculty of Sciences In Collaboration with Ecole´ des Mines de Nantes 2001-2002 Applying Prototype-Based Programming Techniques for the Organization of Mobile Systems A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Computer Science (Thesis research conducted in the EMOOSE exchange project funded by the European Community) By: Boris Mej´ıas Promotor: Prof. Theo D’Hondt (VUB) Advisor: Wolfgang De Meuter (VUB) Abstract Agents succeeded as mobile entities that properly solved problems on mobile systems. They can move around the network in a transparent way, and communi- cate with other agents by sending messages. But the relationship between agents does not have a strong structure, and big multi agent systems become hard to maintain and to understand. The primary aim of this work is to provide a way to organize agents in mobile systems. Objects help us to have a structured way of programming, but if we want ob- jects moving around different address spaces, we need them to be self-supporting. When objects depends on a class, we also need to move the class everywhere the object goes, and to have a sophisticated system for type checking. We decided to use Prototype-Based Programming, a paradigm to program without classes, which has a proper way of reasoning about sharing, an important property for our purpose to organize the system. We extend Borg, a language to implement autonomous agents in a wide area network. The extension provides methods to create prototypes that can move and be extended through the network.
    [Show full text]
  • The X in Ajax
    JSON The x in Aja x Douglas Crockford Yahoo! Inc. YAHOO IS HIRING DEVELOPERS Ajax, PHP, DHTML/XHTML, Javascript, CSS, Actionscript / Flash Josie Aguada [email protected] Data Interchange • The key idea in Ajax. • An alternative to page replacement. • Applications delivered as pages. • How should the data be delivered? History of Data Formats • Ad Hoc • Database Model • Document Model • Programming Language Model JSON • JavaScript Object Notation • Minimal • Textual • Subset of JavaScript JSON • A Subset of ECMA-262 Third Edition. • Language Independent. • Text-based. • Light-weight. • Easy to parse. JSON Is Not... • JSON is not a document format. • JSON is not a markup language. • JSON is not a general serialization format. No cyclical/recurring structures. No invisible structures. No functions. History • 1999 ECMAScript Third Edition • 2001 State Software, Inc. • 2002 JSON.org • 2005 Ajax • 2006 RFC 4627 Languages • Chinese • English • French • German • Italian • Japanese • Korean Languages • ActionScript • Perl • C / C++ • Objective-C • C# • Objective CAML • Cold Fusion • PHP • Delphi • Python • E • Rebol • Erlang • Ruby • Java • Scheme • Lisp • Squeak Object Quasi-Literals • JavaScript • Python • NewtonScript Values • Strings • Numbers • Booleans • Objects • Arrays • null Value Strings • Sequence of 0 or more Unicode characters • No separate character type A character is represented as a string with a length of 1 • Wrapped in "double quotes " • Backslash escapement String Numbers • Integer • Real • Scientific • No octal or hex • No NaN or Infinity Use null instead Number Booleans • true • false null • A value that isn't anything Object • Objects are unordered containers of key/value pairs • Objects are wrapped in { } • , separates key/value pairs • : separates keys and values • Keys are strings • Values are JSON values struct, record, hashtable, object Object Object {"name":"Jack B.
    [Show full text]
  • On the Interaction of Method Lookup and Scope with Inheritance and Nesting
    On the Interaction of Method Lookup and Scope with Inheritance and Nesting Gilad Bracha Cadence Design Systems [email protected] Abstract. Languages that support both inheritance and nesting of dec- larations define method lookup to first climb up the inheritance hierar- chy and then recurse up the lexical hierarchy. We discuss weaknesses of this approach, present alternatives, and illustrate a preferred semantics as implemented in Newspeak, a new language in the Smalltalk [GR83] family. 1 Introduction The combination of inheritance and block structure is potentially very powerful, as shown in the language Beta [MMPN93], and later languages such as gBeta [Ern01] and Scala [Ode07]. The idea has gained currency in the mainstream with the introduction of nested classes in JavaTM 1. In all these languages, situations such as the following (illustrated in Java) can arise: class Sup {} class Outer { int m(){ return 91} class Inner extends Sup { int foo(){return m()} // case 1: new Outer.Inner().foo() = 91 } } The expectation is that a call to foo will yield the result 91, because it returns the result of the call to m, which is defined in the enclosing scope. In general, the semantics of a method invocation that has no explicit target (receiver) are that method lookup begins by searching the inheritance hierarchy of self (aka this); if no method is found, then the lookup procedure is repeated recursively at the next enclosing lexical level. This notion is described in detail in the Java Language Specification [GJSB05] and formalized in [SD03]. It is called 1 Java is a trademark of Sun Microsystems.
    [Show full text]