A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
A MOO is a text-based online virtual reality system to which multiple users are connected at the same time.The term MOO is used in two distinct, but related, senses...
Prototype-based programming is a style of object-oriented programming in which classes are not present, and behavior reuse is performed via a process of cloning existing objects that serve as prototypes. This model can also be known as classless, prototype-oriented or instance-based programming...
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
In computer science, the syntax of a programming language is the set of rules that define the combinations of symbols that are considered to be correctly structured programs in that language. The syntax of a language defines its surface form...
roughly derived from the Algol school of programming languages.
History
Stephen White authored the first MOO Server and language in 1990 using C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
. Over the course of the year, Pavel Curtis joined the project, releasing the first version of the LambdaMOO
LambdaMOO
LambdaMOO is an online community of the variety called a MOO. It is the oldest MOO today.LambdaMOO was founded in late 1990 or early 1991 by Pavel Curtis at Xerox PARC. Now hosted in the state of Washington, it is operated and administered entirely on a volunteer basis...
Server. LambdaMOO is run and maintained entirely on a volunteer basis, and now has its own SourceForge
SourceForge.net
SourceForge is a web-based source code repository. It acts as a centralized location for software developers to control and manage open source software development. The website runs a version of SourceForge Enterprise Edition, forked from the last open-source version available...
project. Although the last packaged release was in 2000, development is still active in the project's CVS.
White describes MOO as "a mishmash of c-like operators and ada-like control structures, combined with prototype-style single-inheritance."
Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of exceptions, special conditions that change the normal flow of program execution....
control flow, as well as traditional looping constructs. A verb and property hierarchy provides default values to prototype objects, with over-riding values lower in the hierarchy. This hierarchy of objects is maintained through delegation to an object's "parent" property, resulting in a form of single inheritance. Special security-related attributes of objects, verbs, and properties include ownership, and read, write and execute flags. MOO programs are byte-code compiled, with implicit decompilation when editing, providing a canonical form of programs.
Persistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
through periodic checkpoints. Objects are identified by a unique integer identifier. Unused program data is eliminated through automatic garbage collection
Garbage collection (computer science)
In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program...
In computer science, reference counting is a technique of storing the number of references, pointers, or handles to a resource such as an object, block of memory, disk space or other resource...
). However, MOO objects themselves are not garbage collected and are manually deleted by their owners or superusers (aka wizards) through a process called 'recycling.'
MOO is explicitly a multi-user system and programs (verbs) are contributed by any number of connected users. A distinction is made between the 'driver' (runtime) and 'core' (programs written in the MOO language.) The vast majority of the functionality of a running MOO is handled 'in-core.'
The runtime supports multi-tasking using a retribution based time slicing method. Verbs run with exclusive access to the database, so no explicit locking is necessary to maintain synchronization. Simple TCP/IP messaging (telnet compatible) is used to communicate with client sockets, each of which is identified with a 'player' in the Virtual reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...
representation system.
The language supports weak references to objects by number, and to properties and verbs through strings. Built-in functions to retrieve lists of properties and verbs exist, giving the language runtime facilities for reflection
Reflection (computer science)
In computer science, reflection is the process by which a computer program can observe and modify its own structure and behavior at runtime....
. The server also contains support for wildcard verb matching, so the same code can easily be used to handle multiple commands with similar names and functions.
Available sequence types in MOO are lists and strings. Both support random access, as well as head and tail operations similar to those available in Lisp
Lisp programming language
Lisp is a family of computer programming languages with a long history and a distinctive, fully parenthesized syntax. Originally specified in 1958, Lisp is the second-oldest high-level programming language in widespread use today; only Fortran is older...
. All operations on lists and strings are non-destructive, and all non-object datatypes are immutable. Built-in functions and libraries allow lists to also be used as associative arrays and ordered and unordered sets.
Control Structures
MOO has a very basic set of control structures, with for-in-list being the only "fancy" feature.
A "Hello world" program is a computer program that outputs "Hello world" on a display device. Because it is typically one of the simplest programs possible in most programming languages, it is by tradition often used to illustrate to beginners the most basic syntax of a programming language, or to...
can be written in MOO as:
@program hello:run
player:tell("Hello to the world of MOO!");
.
A more interesting example:
@program toy:wind
if (this.location player)
if (this.wound < this.maximum)
this.wound = this.wound + 2;
player:tell("You wind up the ", this.name,".");
player.location:announce(player.name, " winds up the ", this.name,".");
if (this.wound >= this.maximum)
player:tell("The knob comes to a stop while winding.");
endif
else
player:tell("The ",this.name," is already fully wound.");
endif
else
player:tell("You have to be holding the ", this.name,".");
endif
.
The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.
