Features
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.'
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 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.
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