Stephen White authored the first MOO Server and language in 1990 using C. Over the course of the year, Pavel Curtis joined the project, releasing the first version of the LambdaMOO Server. LambdaMOO is run and maintained entirely on a volunteer basis, and now has its own SourceForge project. Although the last packaged release was in 2001, development is still active in the project's CVS, on Sourceforge.net Some follow-on code is also available on Github.net White describes MOO as "a mishmash of c-like operators and Ada-like control structures, combined with prototype-style single-inheritance."
Features
The language has explicit exception handlingcontrol 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. MOO programs are orthogonally persistent through periodic checkpoints. Objects are identified by a unique integer identifier. Unused program data is eliminated through automatic garbage collection. However, MOO objects themselves are not garbage collected and are manually deleted by their owners or superusers through a process called 'recycling.' MOO is explicitly a multi-user system and programs are contributed by any number of connected users. A distinction is made between the 'driver' and 'core' 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 is used to communicate with client sockets, each of which is identified with a 'player' in the Virtual reality 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. 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. 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.
Syntax
Control Structures
MOO has a very basic set of control structures, with for-in-list being the only "fancy" feature.
if ... else
if ; elseif ; else ; endif
for
for in ; endfor
for in ; endfor
while
while ; endwhile
try ... except
try ; except ; endtry
Example Programs
The classic Hello World Program can be written in MOO as: @program hello:run player:tell;
A more interesting example: @program toy:wind if if this.wound = this.wound + 2; player:tell; player.location:announce; if player:tell; endif else player:tell; endif else player:tell; endif .
