What’s new in Inform 7?

Inform 7 was released on 30 April 2006, ten years to the day since the last major upgrade of the Interactive Fiction authoring system. And it’s an exciting leap forward.

But first, what is Inform 6?

Inform 6 is one of the most popular IF authoring systems. It was released on 30 April 1996 and has been more-or-less stable since then. The complete system consists of two parts: the compiler and the library. As with any programming language, the compiler is the practical implementation of the language. But more significant is the library, which itself has two parts: the parser and the world model. The parser contains the procedures for “understanding” the player’s English language instructions. The world model includes all of the rules for making the game world work consistently (e.g. objects stay where they are put, descriptions of the game world reflect the changing events in the story) and preventing ludicrous things from happening (e.g. the player can’t eat a table) unless specifically programmed otherwise. Together the compiler and library convert valid source code into Inform story files that can be read by any Z-machine interpreter.

The architecture of Inform is extensible, allowing reusable packages of extra rules to be added to the standard library to bring more sophisticated “behaviour” to IF stories. An abundance of third-party extensions has been contributed to the IF archive over the years, including some that completely replace the standard library.

Inform 7

Unlike most software upgrades, Inform 6 is not superseded by Inform 7. In fact Graham Nelson says that Inform 6 remains “an essential part of the inner workings of Inform 7.” The new version of Inform includes an Integrated Development Environment (IDE), currently available for Windows and OS X, and a “natural language” dialect.

It’s got some IDE

Graham Nelson deliberately avoids using the term IDE in reference to Inform 7; he prefers to think of it as an application with a book metaphor, saying in his announcement on r.a.i.f.:

The Inform user interface is based on a writer’s manuscript book, opened to show facing pages. The author writes on one page, Inform replies on the other. This dialogue is not carried out in the traditional form of computer programs, but in natural language.

screen capture of Inform 7 in action
Inform 7’s book metaphor: code on the left, game play on the right

Nevertheless, it most definitely is a new IDE that includes a source editor with syntax highlighting, system documentation, integrated Z-machine interpreter, and tools for recording activity in the interpreter (transcript and skein). Features of the IDE include single step compile and run, the ability to replay the previous sequence of instructions on a newly compiled game, detailed (and often even helpful) error messages, an index that allows various views on the structure of the story (including a graphical world map), and automatic packaging of stories for public release.

screen capture of Inform 7 in action
Inform 7’s transcript feature

It’s worth expanding a bit about the skein. While play-testing a game in Inform 7, all commands issued are recorded for later possible playback. The skein represents those commands as a tree, showing common threads and diversions in paths that have previously been taken through the story. Along with the transcript, the skein is a powerful debugging tool, allowing a bit of tinkering with the command history and the ability to replay a specific sequence of commands to a given point. All good stuff when sorting out what’s going on (and wrong) in a story.

screen capture of Inform 7 in action
The skein is a tree representation of all moves made in the game

It’s only natural

Many would think the IDE alone would be improvement enough, but the addition of a kind of natural language programming is a pretty exciting innovation too. Here’s an example - a small section of the classic Colossal Cave, taken from the Inform 7 documentation:

“Cave Entrance”

The Cobble Crawl is a room. “You are crawling over cobbles in a low passage. There is a dim light at the east end of the passage.”

A wicker cage is here. “There is a small wicker cage discarded nearby.”

The Debris Room is west of the Crawl. “You are in a debris room filled with stuff washed in from the surface. A low wide passage with cobbles becomes plugged with mud and debris here, but an awkward canyon leads upward and west. A note on the wall says, ‘Magic word XYZZY’.”

The black rod is here. “A three foot black rod with a rusty star on one end lies nearby.”

Above the Debris Room is the Sloping E/W Canyon. West of the Canyon is the Orange River Chamber.

Yes programmers, that is a code listing. Not a particularly exciting story as it stands, but it’s valid Inform 7 code that compiles and runs. Some programmers will hate this verbose, pseudo-English style of programming and others will love it. The possible benefits and drawbacks for inexperienced programmers are being actively debated on r.a.i.f. and the jury is still out. After absorbing the Inform 7 documentation, I think beginners would be well advised to skim through the Inform Designer’s Manual (which covers Inform 6) to get a better feel for what’s going on behind the scenes.

screen capture of Inform 7 in action
Inform 7 automatically built this graphical world map from the above code


Inform 6 remains the underlying compiler, so the natural language aspect of Inform 7 is essentially “syntactic sugar” - a pleasant layer over the mundane details of Inform 6 code. Of course Inform 7 code isn’t really prose and the compiler doesn’t really understand natural language: the grammar rules are stricter than normal English and you can’t just say anything and Inform 7 will understand - it still needs to be programmed. In my initial dabbling with Inform 7 I’ve found that I can’t follow if-then and repeat loops without indentation, so my code doesn’t look much like ordinary written language.

Possibly the best thing about the natural language approach is not immediately obvious - the ease of writing new rules for the game world. To my mind, it’s easier and more “human” to write your rules out in English than in the more formal logic of unsweetened Inform 6 code. For example, something like this (from Emily Short’s worked example “Bronze”):

Instead of taking the jigsaw puzzle: say “If you took it, the pieces would fall apart.”

Or this (from the Inform 7 documentation):

Instead of eating something in the presence of Lady Bracknell, say “Lady Bracknell disapproves thoroughly of gentlemen who snack between meals, and there are few disapprovals in this world quite so thorough as Lady Bracknell’s.”

These are pretty shallow examples but the same idea is easily extended to do some really sophisticated things in the game world.

Time will tell if this natural language approach is a practical way to write programs, but it seems like fun and the ability to phrase simulation rules in recognisable English is powerful.

Polished performer

Graham Nelson and his team have been working on Inform 7 for three years; and the effort has been well worth it. At the time of writing Inform 7 is in public beta release, so a few rough edges are to be expected but it is a polished and professional offering. The new tools in the IDE are incredible and incredibly useful and they can only help speed the IF development process in Inform. And the natural language implementation is an exciting initiative. Sure it’s not “real” natural language but it has the potential to attract new authors to Interactive Fiction and rekindle the interest of those who have put IF on the backburner.

Now if you’ll excuse me, I’ve got to go and dust-off some long-abandoned IF projects…

First published: PC Update June 2006