Welcome to Inform, a design system for interactive fiction based on natural language.
Interactive fiction is a literary form which involves programming a computer so that it presents a reader with a text which can be explored. Inform aims to make the burden of learning to program such texts as light as possible. It is a tool for writers intrigued by computing, and computer programmers intrigued by writing. Perhaps these are not so very different pursuits, in their rewards and pleasures.
The sheer joy of making things... the fascination of fashioning complex puzzle-like objects of interlocking moving parts and watching them work in subtle cycles... the delight of working in such a tractable medium. The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds his castles in the air, from air, creating by exertion of the imagination. (Frederick P. Brooks, "The Mythical Man-Month", 1972)
Writing with Inform is one of two interlinked books included with Inform: a concise but complete guide to the system. The other book is The Inform Recipe Book, a comprehensive collection of examples, showing its practical use.
These notes are arranged so that the reader can, in principle, write whole works of fiction as early as the end of Chapter 3. Each subsequent chapter then extends the range of techniques available to make livelier and more intriguing situations.
Today's Inform language (sometimes called "Inform 7") is very different from its 20th-century predecessor, which was called Inform 6. A few advanced sections of this book show how unusual effects can be achieved by mixing low-level coding in Inform 6 notation with more usual Inform text. However, most users will never need this. For information about Inform 6, see inform-fiction.org.
This book is also a guide to the Inform language, rather than a manual on how to use its supporting tools. Those tools, when used at the command line rather than inside the Inform app, have numerous features not covered here. Manuals for them are all available online: see github.com/ganelson/inform.
Programming is best regarded as the process of creating works of literature, which are meant to be read... so we ought to address them to people, not to machines. (Donald Knuth, "Literate Programming", 1981)
Inform 7 is dedicated to Emily Short and Andrew Plotkin, whose shrewd and sceptical suggestions made a contribution which can hardly be overstated. A long email correspondence with Andrew entirely subverted my original thoughts about natural-language IF, as he convinced me that the "new model" of rule-based IF was a truer foundation; while Emily's wry, witty analysis and how-about-this? cheered me at low moments, besides providing the impetus and often the specifics for a lot of the best ideas.
From the outset, I have thought of Inform 7 as no longer being a command-line compiler, but a compiler in combination with a humanising user interface. All credit for the reference implementation under Mac OS X belongs to Andrew Hunter. How simple the metaphor of an interactive book with facing pages may seem, but the coding was an enormous challenge. In 2014 Toby Nelson, my brother, put months of time into the project by rewriting and modernising the Mac OS X application: sandboxing it for the Mac App Store, giving it a more contemporary design, and much more. He continues to maintain it today.
Though David Kinder's Windows application does indeed visually follow the OS X original, the two programs were coded independently, and the programming task taken up by David was formidable indeed. Philip Chimento's Gnome-based user interface for Linux became officially part of the project in November 2007, when the first easy-to-install packages for Ubuntu and Fedora were offered. Adam Thornton gave invaluable assistance in the closed-source age of Inform to make generic Unix binaries available, too.
While Inform is not strictly speaking a project of the Interactive Fiction Technology Foundation (IFTF), it benefits enormously from the Foundation's good work. In particular, the Narrascope conferences were invaluable in the period 2017-2022, and I thank Judith Pintar and Andrew Plotkin for arranging speaking slots at them.
Inform in its widest sense incorporates work by so many people that it's simply impossible to thank all of them, but Zed Lopez, Dannii Willis, Mark Musante, Brian Rushton, Dan Fabulich, Hugo Labrande, Erik Temple, Ron Newcomb, Eric Eve, Justin de Vesine and Juhana Leinonen all deserve special mention. Many hundreds of users have filed patient and careful bug reports, keeping us on the straight and narrow. They're contributors, too.
The original development of Inform 7 was a long haul, and I would particularly like to thank Sonja Kesserich, David Cornelson and other volunteers for their early testing of a then-fragile system. The final months before the Public Beta release of Inform 7 were made more enjoyable, as well as more productive, by fruitful discussions leading to a cross-platform standard for bibliographic data and cover art. Special mentions to L. Ross Raszewski, who wrote frighteningly efficient reference software in frighteningly little time; the librarians of the IF-Archive, Andrew Plotkin, David Kinder and Paul Mazaitis; and my fellow authors of IF design systems - Mike Roberts (of the Text Adventure Development System); Kent Tessman (of Hugo); and Campbell Wild (of ADRIFT).
At the start the only panels available are a blank space in which to write the first lines of a new interactive fiction - the Source panel - and this one, the Documentation. Clicking on the other choices will do nothing.
The exception is the Settings panel, which contains some preference settings for the individual project - not the whole application. This is always available, but it controls settings which can be left alone almost all of the time.
Clicking the Go button translates the text in the Source panel into a computer program which enacts the interactive fiction, and automatically sets it going (in the Story panel, which opens as needed).
If the Source is empty of text, Inform will be unable to create anything: it needs at least one name of a location where the drama can unfold. For reasons of tradition, such locations are normally called "rooms", though people have used them to represent anything from grassy fields to states of mind and other metaphorical places.
"Midsummer Day"
The Gazebo is a room.
Clicking Go with this text in the Source panel will result in a short delay, after which the Story panel will appear, from which we can explore this newly created world: an interactive fiction called "Midsummer Day". It will not be very exciting, since Inform has only five words to go on, but we can add more detail to the source at any point and then click Go again to try out the changes. (Note that there is no need to "quit" these explorations in the Story panel. When Go is clicked, any story already in progress is discarded in favour of the new version.)
Replay works identically to Go, except that it does something further: once the story is created, it automatically plays through the same commands as were typed into the previous version. For instance: suppose we click Go to bring Midsummer Day into being, and find ourselves playing the story. We type "look" and find that there is not much to see. Going back to the source, we add
"A white canvas parasol raised up on stakes driven into the grass."
so that the source now reads
"Midsummer Day"
The Gazebo is a room. "A white canvas parasol raised up on stakes driven into the grass."
Instead of clicking Go, we click Replay, and can sit back and watch what has changed. In this example, it only saves us the trouble of typing "look", but once stories become long and elaborate, Replay is invaluable: and especially when we notice in play that something very minor is wrong - a spelling error, say - and want to fix it immediately, without fuss.
If, when Go! is clicked, the text in the Source panel is not fully understood, then Inform will generate a report of the problems it found, which will open in the "Errors" panel. (Other information is also available in "Errors", but most of it is used for debugging Inform, and can be ignored.)
On the other hand, if the text was fully understood then another new panel will become available: the "Index". This is a cross-referenced index of the source, or rather, of the interactive fiction which has been generated. The Index is only an optional convenience, but becomes more and more helpful as the fiction grows larger. Its exact format does not matter for now.
The icon always denotes a reference to a particular line in the Source text, that is, to something written in the source: clicking it opens the Source panel and jumps to that position.
The icon indicates that more detailed information can be read further down the text in the same panel: clicking it jumps down to this more detailed report.
Lastly, the icon hints that there is a relevant page of this manual: clicking this opens the Documentation panel and switches to it.
The Replay button demonstrates that Inform must be quietly remembering the commands typed into the last run through the story. In fact it remembers, and automatically organises, every previous run.
Inform's approach to testing interactive fiction is to treat it as being like the analysis of other turn-based games, such as chess. It would be prohibitively difficult to work out every possible combination of moves: instead, we analyse those which go somewhere, and look for significant choices. Every Queen's Gambit begins with the same first three moves (1. d4, d5; 2. c4), but then there is a choice, as the next move decides whether we have a Queen's Gambit Accepted (dxc4) or Declined (e6). Books about chess often contain great tables of such openings, which run together for a while but eventually diverge. To learn chess, one must explore all of these variations.
Inform's Skein panel is just such a table, built automatically. If we think of the list of typed commands as a thread, then the skein is (as the name suggests) braided together from all these threads. In the display, time begins at the top, with the start knot, and the threads of different play-throughs hang downwards from it.
Double-clicking on a command translates the source afresh and replays the story from start down to that command, and then stops. We are then free to continue play by typing commands into the Story panel, of course, and these commands will automatically be recorded in the Skein as a new variation of play, diverging from the previous threads.
The user interface for the Skein looks slightly different on different versions of the Inform apps (that is, the MacOS version is not quite the same as the Windows version, and so on), so this manual is not the best place to describe it. In any case, the best way to find out about it is probably to experiment.
always denotes a reference to a particular line in the Source text, that is, to something written in the source: clicking it opens the Source panel and jumps to that position.
indicates that more detailed information can be read further down the text in the same panel: clicking it jumps down to this more detailed report.
hints that there is a relevant page of this manual: clicking this opens the Documentation panel and switches to it.