MOO (programming language)

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The MOO programming language is a relatively simple programming language used to support the MOO Server. It is dynamically typed and uses a prototype based object oriented system, with syntax roughly derived from the Algol school of programming languages.



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 2000, development is still active in the project's CVS.[1]

White describes MOO as "a mishmash of c-like operators and ada-like control structures, combined with prototype-style single-inheritance."


The language has explicit exception handling 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.

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 (implemented by reference counting). 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.'

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