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<HTML><HEAD><TITLE>Introduction</TITLE></HEAD>
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<TABLE><TR><TD Valign="top"><A HREF="contents.html">Contents</A><BR><A HREF="contents.html">Back</A><BR><A HREF="chapter1.html">Forward</A><TD bgcolor="#F5DEB3"><BLOCKQUOTE><H3>Introduction</H3>
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</BLOCKQUOTE><TR><TD><TD>
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<BR>I will build myself a copper tower
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<BR>With four ways out and no way in
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<BR>But mine the glory, mine the power...
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<BR><P>...Louis MacNeice (<B>1907</B>--<B>1963</B>), <I>Flight of the Heart</I></BLOCKQUOTE>
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Inform is a system for creating adventure games, and this is the book to
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Infocom format 'story files' (adventure games, that is) can be played on
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almost any computer, from personal organisers to mainframes, with the aid of
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'interpreter' programs. The task of the Inform 'compiler' is to translate a
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textual description of a game into a story file. The result will play
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identically on any machine of any model.
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Inform is a suite of software, called the 'library', as well as a compiler.
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Without the library, it would be a major undertaking to write a description
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of even the smallest game. The library has two ingredients: the parser, a
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program for translating written English inputs into a form games can more
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easily understand, and the "world model'', a complex web of rules common
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to all adventure games. Given these, the designer only needs to describe
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things and give any exceptional rules that apply. ("There is a bird here,
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which is a normal item except that you can't pick it up.'')
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The library is rich in detail. The parser recognises over 80 distinct verbs
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and a vocabulary of about 300 words even before any rooms or objects are
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created, and is programmable and highly flexible. It can handle ambiguities,
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clarify its input by asking questions ("Which key do you mean...?'') and can
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cope properly with plurals, vagueness, conversation, pronouns and the player
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becoming someone else in mid-game. It can be configured to languages other
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than English. The world-model includes rooms, items, vehicles, duplicates,
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containers, doors, things on top of other things, light and darkness,
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switching things on and off, opening, closing and locking things, looking
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up information in books, entering things, scoring and so forth.
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Just as Inform has two strands -- compiler and library -- so this manual has
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two parts: Programming and Designing. In Book One, small computer programs
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are written to perform simple calculations, never using the library. Subsections
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listed <I> in slanted text</I> on the detailed contents page become technical
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but the rest is pitched at newcomers and can be skim-read by anyone with
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prior experience of a programming language such as C or Pascal. Book Two
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is entirely about making games.
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Newcomers are invited to work through <A HREF="section1.html">Section 1</A> and <A HREF="section7.html">Section 7</A>, the "getting started''
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sections in Books One and Two, before reading much more of either.
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In trying to be both a tutorial and reference work, this book aims itself
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in style halfway between the two extremes of manual, Tedium and Gnawfinger's
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<I> Elements of Batch Processing in COBOL-66</I>, third edition, and Mr Blobby's
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<I> Blobby Book of Computer Fun</I>. (This makes some sections both leaden
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<I> and</I> patronising.)
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<P><TR><TD Valign="top"><IMG SRC="icons/dbend.gif" ALT="/\"><TD bgcolor="#EEEEEE"><SMALL> Passages which divert the main story, usually to
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tell an unexpurgated truth which may confuse or bore a newcomer, are marked
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with a warning triangle <IMG SRC="icons/dbend.gif" ALT="/\"> or two, and set in smaller type.
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Examples of program are set in <TT>typewriter</TT> font.
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Mundane or irrelevant passages in
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longer examples are sometimes replaced with a line reading just "<TT>...</TT>''
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To keep Book Two from clogging up with examples, many are set as
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"exercises'', with "answers'' given in full at the back of the book.
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Harder exercises are marked with triangles and some are very hard indeed.
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I emphasize that the exercises are often intended as a way of presenting answers
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to deliberately difficult questions, to assist experts: the curse of Adventure
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design-languages is the feature which is ideal for the simple but too inflexible
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to cope with the complicated. For a list of exercises with page references to
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question and answer, see under "exercises'' in the Index.
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A better tutorial than attempting the exercises, then, is probably to make
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a simple game, as demonstrated in Chapter III, and then add an example of each
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new feature as you work through Chapters IV and V.
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Many sections end with a 'References' paragraph referring to yet
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more examples which can be found in Inform's demonstration games. All of these
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have publically available source code (see the Inform home page): those most
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frequently referred to are 'Advent' (a full version of the original
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mainframe 'Adventure', which contains a good deal of "everyday Inform''),
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'Adventureland' (a version of Scott Adams's primitive classic),
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'Alice Through The Looking-Glass' (a heavily annotated game, developed in
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the course of Gareth Rees's WWW tutorial for Inform), 'Balances' (a short
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story consisting of puzzles which stretch the parser's abilities) and
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'Toyshop' (hardly a game: more an incoherent collection of unusual
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objects). In addition, the little game 'Ruins' is developed
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in the course of Chapters III and IV of this manual.
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Finally, the "game'' called 'Museum of Inform' simulates a museum whose
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exhibits are solutions to the exercises in this manual.
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Copyright on Inform, the program and its source code, its example games
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and documentation (including this book) is retained by Graham Nelson, who
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asserts the moral right to be identified as the author under the Copyrights,
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Designs and Patents Act 1988. Having said this, I am happy for it to be freely
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distributed to anybody who wants a copy, provided that: (a) distributed copies
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are not substantially different from those archived by the author, (b) this and
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other copyright messages are always retained in full, and (c) no profit is
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involved. (Exceptions to these rules must be negotiated directly with the
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author.) However, a story file produced with the Inform compiler (and
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libraries) then belongs to its author, and may be sold for profit if desired,
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provided that its game banner contains the information that it was compiled by
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Inform, and the Inform version number.
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The Internet source for Inform material (executables of the compiler for
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different machines, source code, the library files and example games)
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is the German National Research Centre for Computer Science, where Volker
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Blasius maintains an archive at the anonymous FTP site <TT>ftp.gmd.de</TT>.
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Inform can be found at:
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<BLOCKQUOTE><A HREF="ftp://ftp.gmd.de/if-archive/infocom/compilers/inform"><TT>ftp://ftp.gmd.de/if-archive/infocom/compilers/inform6</TT></A></BLOCKQUOTE>
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Another useful resource is the Inform 6 home page on the 'World Wide Web',
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which includes Gareth Rees's 'Alice' tutorial, located at:
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<BLOCKQUOTE><A HREF="http://www.gnelson.demon.co.uk/inform.html"><TT>http://www.gnelson.demon.co.uk/inform.html</TT></A></BLOCKQUOTE>
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This manual describes Inform release 6.13 (or later), using
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library release 6/5 (or later). Earlier Inform 6 compilers and
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libraries are very similar but Inform 5.5 and 5/12 are very different.
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This manual has evolved from seven earlier publications, once rather makeshift
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and sometimes defensive ("Inform is an easel, not a painting''). There were
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specifications of the run-time code format and literary critiques of games
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gone by: like an oven manual padded out with both a cookery book and a
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detailed plan of the gas mains. This book contains just the instructions
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So there are four 'companion volumes'. <I> The Craft of Adventure</I> is
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an essay on the design of adventure games; <I> The Z-Machine Standards
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Document</I> minutely covers the run-time format and Inform assembly
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language, its lowest level; and <I> The Inform Technical Manual</I> documents
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Inform's internal working in great detail, and includes a formal context-free
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grammar for the Inform language. The <I> Inform Translator's Manual</I>
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describes how to write a language definition file for games which speak
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languages other than English.
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Some of the ideas of Inform came from an incremental multi-player
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game called Tera, on the Cambridge University mainframe, written by
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Dilip Sequeira and the author in 1990 (whose compiler was called Teraform);
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in turn, this stole a little from David Seal and Jonathan Thackray's
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game assembler; which dates back to the close of the 1970s and was written for
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'Acheton', perhaps the first worthwhile game written outside America.
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Still, much of the Inform kernel derives ultimately from the <I> IEEE Computer</I>
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article 'Zork: A Computerized Fantasy Simulation Game' by P. David Lebling,
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Marc S. Blank and Timothy A. Anderson; and more was suggested by
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Richard Tucker and Gareth Rees, among others.
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The list of those who have helped the project along is legion: I should like
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to thank them all, porters, users and critics alike, but especially Volker
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Blasius, Paul David Doherty, Mark Howell, the ever avuncular Bob Newell, Robert
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Dilip Sequeira, Richard Tucker,
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Christopher Wichura and John Wood.
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One final word. I should like to dedicate this book, impertinently perhaps,
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to our illustrious predecessors: Will Crowther, Don Woods and
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the authors of Infocom, Inc.
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<TR><TD><TD align="right"><I>Graham Nelson</I>
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<TR><TD><TD align="right"><I>Oxford</I>
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<TR><TD><TD align="right"><I>April 1993 -- May 1997</I>
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<BR>And if no piece of chronicle we prove,
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<BR>We'll build in sonnets pretty rooms;
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<BR>As well a well wrought urn becomes
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<BR>The greatest ashes, as half-acre tombs.
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<BR><P>...John Donne (<B>1571</B>?--<B>1631</B>), <I>The Canonization</I></BLOCKQUOTE>
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<HR><A HREF="contents.html">Contents</A> / <A HREF="contents.html">Back</A> / <A HREF="chapter1.html">Forward</A> <BR>
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<A HREF="chapter1.html">Chapter I</A> / <A HREF="chapter2.html">Chapter II</A> / <A HREF="chapter3.html">Chapter III</A> / <A HREF="chapter4.html">Chapter IV</A> / <A HREF="chapter5.html">Chapter V</A> / <A HREF="chapter6.html">Chapter VI</A> / <A HREF="chapterA.html">Appendix</A><HR><SMALL><I>Mechanically translated to HTML from third edition as revised 16 May 1997. Copyright © Graham Nelson 1993, 1994, 1995, 1996, 1997: all rights reserved.</I></SMALL></BODY></HTML>
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