Inform is a programming language and design system for interactive fiction, created in 1993 by Graham Nelson.

=Overview=

The Inform system properly consists of two major components: the Inform compiler, which generates story files from Inform source code, and the Inform library, a suite of software which handles the most difficult work of parsing the player s input and keeping track of the world model. The name Inform also refers to the Inform programming language that the compiler understands.

=The compiler=

The Inform Compiler generates files in Z-machine (also called story files) from Inform sourcecode. These files can then be run by any Z-code interpreter -- that is, by any program which properly emulates the Z-code virtual machine. Because there is at least one such interpreter for nearly every major and minor platform, this means that the same Z-code file can be run on a multitude of platforms with no alterations.

Andrew Plotkin created an unofficial version of Inform that is capable of generating files for the Glulx virtual machine, which removes many of the limitations of the Z-machine. He also created a compiler for both the Z-machine and Glulx. However, the Glulx virtual machine is not as widely ported. Inform 6.3, released February 29, 2004, includes official support for both virtual machines, based on Andrew Plotkin s work.

Although Inform and the Z-Machine were originally designed with interactive fiction in mind, a large number of other programs have been developed, including a BASIC programming language interpreter, a Tetris game, and a version of the game Snake.

=The programming language=

The Inform programming language is object-oriented and procedural programming. A key element of the language is objects. Objects are maintained in an object tree which lists the parent child relationships between objects. Since the parent-child relationship is often used to represent location, an object which is the parent of another object is often said to hold it. Objects can be moved throughout the tree. Typically top level objects represent rooms and other locations within the game, which may hold objects representing the rooms contents, be they physical items, non-player characters, the player s character, or background effects. All objects can hold other objects, so a livingroom object might hold an insurancesaleman object which is holding a briefcase object which contains the insurancepaperwork object.

In early versions of Inform, objects were different from the notion from object-oriented programming, in that there was no such thing as a class. Later versions added support for class definitions and allowed objects to be members of classes. Objects and classes could inherit from multiple classes. Interactive fiction games typically contain many unique objects. Because of this, many objects in Inform do not inherit from any class, other than the metaclass Object. However, objects very frequently have attributes (boolean properties, such as scenery or edible) that are recognized by the Inform library. In other languages this would normally be implemented via inheritance.

Here is a simple example of Inform source code.

[ Main; print Hello World^ ; ];

=The library=

The Inform system also contains the Inform library, which automates nearly all of the most difficult work involved in programming interactive fiction; specifically, it includes a parser that makes sense of the player s input, and a world model that keeps track of such things as objects (and their properties), rooms, doors, the player s inventory, etc.

Here is an example of Inform source code that makes use of the Inform library:

Include Parser ; Include VerbLib ; [ Initialise; print Hello World^ ; location = livingroom; ]; Object livingroom Living Room with description A comfortably furnished living room. , n_to kitchen, s_to frontdoor, has light; Object salesman insurance salesman livingroom with name insurance salesman man , description An insurance salesman in a tacky polyester suit. He seems eager to speak to you. , before [; Listen: move insurancepaperwork to player; The salesman bores you with a discussion of life insurance policies. From his briefcase he pulls some paperwork which he hands to you. ; ], has animate; Object briefcase briefcase salesman with name briefcase case , description A slightly worn, black briefcase. , has container; Object insurancepaperwork insurance paperwork briefcase with name paperwork papers insurance documents forms , description Page after page of small legalese. ; Include Grammar ;

The Inform compiler does not require the use of the Inform library. At least one replacement library, [http://www.elvwood.org/InteractiveFiction/Platypus/ Platypus], is available.

=Notable games developed in Inform=

=Further reading=

=External links=