Something about Interactive Fiction
Complex Entrance You are standing at the entrance to what appears to be some sort of military complex. This room consists of thick metal walls that are covered in a fine, brown rust, and lumpy metal floors. Directly in front of you is a big hazardous materials canister. To your right is a pillar, containing several monitors that appear to be painted on. There is a corridor leading deeper into the complex to the west, and a door leading back out into the yard to the south.
The above is an excerpt from IF Quake, an interactive fiction game by Jason Bergman. IF Quake doesn’t port the id classic, but it is a playable representation of Quake and, more importantly, a parody. In the example, the main character (the “you” referred to) is in a room called “Complex Entrance.” Interactive fiction games have environments created by a linked series of rooms. The term “room” is used regardless of being an interior or exterior location and, descriptively, can be any shape or size.
The room provides a structural framework. The descriptions of rooms are often painted on, like the monitors in the example. Color text provides dressing for the room, but often isn’t directly important to the playing of the game. For instance, the command >look at rust, brings back the text: You can’t see any such thing. Of more concern are the Grunt, the Rottweiler, the hazardous materials canister, and the medkit. These are the only objects in the room that the player can interact with. However, this isn’t necessarily the case for all interactive fiction games. Some have more depth regarding their creation of a world; others support interactions with characters beyond blowing the bejeezus out of them, and still others have a focus beyond the exploration/combat seen in IF Quake.
The last thing to note is the most important: Interactive fiction games respond to natural language input. In his book Twisty Little Passages: An Approach to Interactive Fiction, Nick Montfort points out that interactive fiction games recognize player input on two levels: Within the game world, and within the realm of the game as a program (saving your game or restoring it, for example). In the example above, the program is recognizing the command to investigate the medkit as well as the command to attack the canister. (Actually, the program seeks to disambiguate what I am shooting the canister with. In some ways, disambiguation works like a helpful Dungeon Master and, in other ways, disambiguation acts as a spoiler: Apparently I will be acquiring more firearms.)
Back to the parser: Early interactive fiction games recognized two-word commands. Later innovations increased the input length, leading to modern day parsers which can often interpret sentences. Parsers diagram the user’s input, extracting direct objects, indirect objects, and verbs. One sophisticated parser (put forth by Magnetic Scrolls) mentioned in Montfort’s book understood the phrase, “plant the plant in the plant pot.” The development of commercial interactive fiction was often distinguished by the growing sophistication of the parser, the growth of the game world, and the improvement of the writing and complexity of game play.