Inform

Inform is a design system and programming language for creating interactive fiction — the text adventures and narrative parser games descended from classics like Zork and Adventure. Created by the British mathematician and IF author Graham Nelson, Inform is unusual among programming languages in that a single name covers two radically different systems: the C-like, object-oriented Inform 6, and the natural-language, rule-based Inform 7. Both compile games down to portable virtual-machine bytecode that runs on interpreters across nearly every platform.

History & Origins

Inform first appeared in 1993, when Graham Nelson built it to write his own game, Curses — itself one of the earliest works of interactive fiction to match the craftsmanship of the commercial games Infocom had produced in the 1980s. Nelson’s goal was deliberately archaeological: rather than invent a new runtime, he targeted Infocom’s existing Z-machine, the virtual machine Infocom had developed in 1979 so that its games could run on the era’s many incompatible home computers. By compiling to Z-code, Inform games could immediately play on the large installed base of Z-machine interpreters.

The early versions (Inform 1 through 5) appeared across 1993–1996, steadily refining the language. In 1996, Nelson rewrote the compiler from first principles to create Inform 6, which introduced the mature object-oriented model that would dominate amateur and noncommercial IF for the next decade. The conceptual debt to Infocom ran deep: Inform was, in spirit, a modern reimplementation of the toolchain behind ZIL (the Zork Implementation Language), aimed at a new generation of authors.

Design Philosophy

Inform 6: code that builds a world

Inform 6 looks like a conventional programming language. It is procedural and object-oriented, with a syntax full of braces and semicolons that will feel familiar to C programmers. The game world is modeled as a hierarchy of objects — rooms, items, characters — each with properties and attributes, and behavior expressed in routines. An author defines what things are, where they sit, and how they respond to the player’s typed commands.

Object  Kitchen "Kitchen"
  with  description "A cramped kitchen. A door leads north.",
  has   light;

Object  apple "red apple" Kitchen
  with  name 'apple' 'red',
        description "A shiny red apple.",
  has   edible;

Inform 7: prose as source code

In 2006, Graham Nelson — working closely with the prominent IF author Emily Short — released Inform 7, which took an entirely different approach. Rather than evolve Inform 6’s syntax, Inform 7 is a declarative, rule-based language whose source code reads like English prose. The author writes assertions about the world and rules that govern it:

The Kitchen is a room. "A cramped kitchen. A door leads north."

The red apple is an edible thing in the Kitchen.
The description of the apple is "A shiny red apple."

Instead of eating the apple:
    say "It is far too perfect to eat."

This natural-language model is one of the most prominent real-world examples of natural-language programming. Crucially, Inform 7 is not a fork of Inform 6 — it is a separate language that, under the hood, translates source into Inform 6 code, which the Inform 6 compiler then turns into the final story file.

Key Features

• Two complementary languages. Inform 6 offers low-level, explicit control; Inform 7 offers high-level, readable rules. Inform 7 can even drop down to embedded Inform 6 when fine-grained control is needed.
• Virtual-machine targets. Games compile to the Z-machine (Infocom’s original format) or to Glulx, a more capacious VM created by Andrew Plotkin to escape the Z-machine’s tight memory ceiling. Glulx support arrived in Inform 6 around 2004 and is now the default target.
• A standard world model. Inform ships with a rich library of default behavior — rooms, containers, doors, light, scenery, conversation — so authors describe their world rather than reimplement parser plumbing.
• A dedicated IDE. Inform 7 is bundled with a graphical development environment built around a book-and-publishing metaphor: source on one side, the compiled game, an index, and a testing “skein” on the other. The IDE is available for Windows, macOS, and Linux (the Linux build is distributed via Flathub).
• Web playback. Compiled games can be played in the browser through bundled JavaScript interpreters — Parchment for the Z-machine and Quixe for Glulx.

Evolution

Inform’s history breaks cleanly into two generations. The Inform 6 generation (1993–2006) established the language as the standard tool of the IF revival, a precise, programmer-friendly system that rewarded careful engineering. The Inform 7 generation (2006–present) reframed authoring around natural language, lowering the barrier for writers without a programming background while keeping the full power of Inform 6 underneath.

A landmark moment came in April 2022, when Inform 7 was open-sourced under the Artistic License 2.0 with release v10.1.0 — ending sixteen years as freeware and opening the compiler internals to the community. Development continues actively on the public GitHub repository, and the classic Inform 6 compiler, now maintained by David Kinder, remains current as well, reaching version 6.42 in early 2024.

Current Relevance

Inform is the dominant authoring system for noncommercial interactive fiction. A large share of entries in the annual Interactive Fiction Competition and other community events are built with it, and many of the form’s most celebrated works — Emily Short’s Counterfeit Monkey, Michael Gentry’s Anchorhead, Adam Cadre’s Photopia — were written in Inform. The open-sourcing of Inform 7 has given the project renewed momentum, with a transparent toolchain and an engaged community on forums such as intfiction.org.

While no official Docker images are published, community-maintained containers exist for headless compilation, and the command-line tools (inform7, inform6, and the blorb packagers) make automated builds straightforward for those who prefer working outside the IDE.

Why It Matters

Inform matters on two distinct levels. As a piece of cultural and technical preservation, it kept Infocom’s Z-machine — and with it an entire genre of storytelling — alive and runnable on modern machines, proving that a 1970s virtual machine could host a thriving creative community decades later. As a language-design experiment, Inform 7 stands as one of the most ambitious and successful attempts at natural-language programming ever shipped, demonstrating that a declarative, prose-like syntax can be both expressive enough for serious authors and approachable enough for newcomers. Few languages straddle the worlds of software engineering and literature as deliberately as Inform.