7 .. image:: /images/picA.png
14 lmost as rarely as an alchemist producing gold from base metal, the
15 compilation process turns your source file into a story file (though the
16 more usual outcome is a reproachful explanation of why -- *again* --
17 that hasn't happened). The magic is performed by the compiler program,
18 which takes your more or less comprehensible code and translates it into
19 a binary file: a collection of numbers following a specific format
20 understood only by Z-code interpreters.
22 On the surface, compilation is a very simple trick. You just run the
23 compiler program, indicating which is the source file from which you
24 wish to generate a game and presto! The magic is done.
26 However, the ingredients for the spell must be carefully prepared. The
27 compiler "reads" your source code, but not as flexibly as a human would.
28 It needs the syntax to follow some very precise rules, or it will
29 complain that it cannot do its job under these conditions. The compiler
30 cares little for meaning, and a lot about orthography, like a most
31 inflexible teacher; no moist Bambi eyes are going to save you here.
33 Although the spell made by the compiler is always the same one, you can
34 indicate up to a point how you want the magic to happen. There are a few
35 options to affect the process of compilation; some you define in the
36 source code, some with ``switches`` and certain commands when you run
37 the program. The compiler will work with some default options if you
38 don’t define any, but you may change these if you need to. Many of these
39 options are provided "just in case" special conditions apply; others are
40 meant for use of experienced designers with advanced and complex
41 requirements, and are best left (for now) to those proficient in the
47 If the source file is not written correctly the compiler will protest,
48 issuing either a *warning* message or an *error* message. Warnings are
49 there to tell you that there may be a mistake that could affect the
50 behaviour of the game at run-time; that won't stop the compiler from
51 finishing the process and producing a story file. Errors, on the other
52 hand, reflect mistakes that make it impossible for the compiler to
53 output such a file. Of these, *fatal* errors stop compilation
54 immediately, while *non-fatal* errors allow the compiler to continue
55 reading the source file. (As you’ll see in a minute, this is perhaps a
56 mixed blessing: while it can be useful to have the compiler tell you
57 about as many non-fatal errors as it can, you'll often find that many of
58 them are caused by the one simple slip-up.)
60 .. rubric:: Fatal errors
62 It's difficult – but not impossible – to cause a fatal error. If you
64 file name as source file, the compiler won’t even be able to start,
67 :samp:`Couldn't open source file {filename}`
69 If the compiler detects a large number of non-fatal errors, it may
70 abandon the whole process with:
72 :samp:`Too many errors: giving up`
74 Otherwise, fatal errors most commonly occur when the compiler runs out
75 of memory or disk space; with today's computers, that's pretty unusual.
76 However, you may hit problems if the story file, which must fit within
77 the fairly limited resources specified by the Z-machine, becomes too
78 large. Normally, Inform compiles your source code into a Version 5 file
79 (that’s what the ``.z5`` extension you see in the output file
80 indicates), with a maximum size of 256 Kbytes. If your game is larger
81 than this, you’ll have to compile into Version 8 file (``.z8``), which
82 can grow up to 512 Kbytes (and you do this very simply by setting the
83 ``-v8`` switch; more on that in a minute). It takes a surprising amount
84 of code to exceed these limits; you won’t have to worry about game size
85 for the next few months, if ever.
88 .. rubric:: Non-fatal errors
90 Non-fatal errors are much more common. You'll learn to be friends with:
92 :samp:`Expected {something} but found {something else}`
94 This is the standard way of reporting a punctuation or syntax mistake.
95 If you type a comma instead of a semicolon, Inform will be looking for
96 something in vain. The good news is that you are pointed to the
97 offending line of code:
99 .. code-block:: transcript
101 Tell.inf(76): Error: Expected directive, '[' or class name but found found_in
103 Compiled with 1 error (no output)
105 You see the line number (76) and what was found there, so you run to the
106 source file and take a look; any decent editor will display numbers
107 alongside your lines if you wish, and will usually let you jump to a
108 given line number. In this case, the error was caused by a semicolon
109 after the description string, instead of a comma:
111 .. code-block:: inform
113 Prop "assorted stalls"
114 with name 'assorted' 'stalls',
115 description "Food, clothing, mountain gear; the usual stuff.";
116 found_in street below_square,
119 Here's a rather misleading message which maybe suggests that things in
120 our source file are in the wrong order, or that some expected
121 punctuation is missing:
123 .. code-block:: transcript
125 Fate.inf(459): Error: Expected name for new object or its textual short name
128 Compiled with 1 error (no output)
130 In fact, there's nothing wrong with the ordering or punctuation. The
131 problem is actually that we've tried to define a new object with an
132 internal ID of ``door`` -- reasonably enough, you might think, since the
133 object *is* a door -- but Inform already knows the word (it's the name
134 of a library attribute). Unfortunately, the error message provides only
135 the vaguest hint that you just need to choose another name: we used
136 ``toilet_door`` instead.
138 Once the compiler is off track and can't find what was expected, it's
139 common for the following lines to be misinterpreted, even if there's
140 nothing wrong with them. Imagine a metronome ticking away in time with a
141 playing record. If the record has a scratch and the stylus jumps, it may
142 seem that the rest of the song is out of sync, when it's merely a bit
143 "displaced" because of that single incident. This also happens with
144 Inform, which at times will give you an enormous list of things Expected
145 but not Found. The rule here is: correct the first mistake on the list
146 and recompile. It may be that the rest of the song was perfect.
148 It would be pointless for us to provide a comprehensive list of errors,
149 because mistakes are numerous and, anyhow, the explanatory text usually
150 indicates what was amiss. You'll get errors if you forget a comma or a
151 semicolon. You'll get errors if your quotes or brackets don't pair up
152 properly. You'll get errors if you use the same name for two things.
153 You'll get errors -- for many reasons. Just read the message, go to the
154 line it mentions (and maybe check those just before and after it as
155 well), and make whatever seems a sensible correction.
159 Warnings are not immediately catastrophic, but you should get rid of
160 them to ensure a good start at finding run-time mistakes (see "Debugging
161 your game" on page 197). You may declare a variable and then not use it;
162 you may mistake assignment and arithmetic operators (``=`` instead of
163 ``==``); you may forget the comma that separates properties, etc. For
164 all these and many other warnings, Inform has found something which is
167 One common incident is to return in the middle of a statement block,
168 before the rest of statements can be reached. This is not always as
169 evident as it looks, for instance in a case like this:
171 .. code-block:: inform
173 if (steel_door has open) {
174 print_ret "The breeze blows out your lit match.";
178 In the above example, the ``print_ret`` statement returns true after the
179 string has been printed, and the ``give match ~light`` line will never
180 happen. Inform detects the fault and warns you. Probably the designer's
184 Compiling *à la carte*
185 ======================
188 One of the advantages of Inform is its portability between different
189 systems and machines. Specific usage of the compiler varies accordingly,
190 but some features should be in all environments. To obtain precise
191 information about any particular version, run the compiler with the
192 ``-h1`` switch -- see "Switches" on page 193.
194 Often the compiler is run with the name of your source file as its only
195 parameter. This tells the compiler to "read this file using Strict mode
196 and from it generate a Version 5 story file of the same name". The
197 source file is mostly full of statements which define how the game is to
198 behave at run-time, but will also include compile-time instructions
199 directed at the compiler itself (although such an instruction looks a
200 lot like a **statement**, it's actually quite different in what it does,
201 and is known as a **directive**). We have already seen the ``Include``
204 :samp:`Include "{filename}";`
206 When the compiler reaches a line like this, it looks for
207 :samp:`{filename}` -- another file also containing Inform code -- and
208 processes it as if the statements and directives included in
209 :samp:`{filename}` were in that precise spot where the ``Include``
212 .. image:: /images/includes.png
215 In every Inform game we Include the library files ``Parser``,
216 ``VerbLib`` and ``Grammar``, but we may Include other files. For
217 example, this is the way to incorporate library extensions contributed
218 by other people, as you saw when we incorporated ``pname.h`` into our
223 on some machines, a library file is actually called -- for example --
224 ``Parser.h``, on others just ``Parser``. The compiler automatically
225 deals with such differences; you can *always* type simply ``Include
226 "Parser";`` in your source file.
228 As you grow experienced in Inform, and your games become more complex,
229 you may find that the source file becomes unmanageably large. One useful
230 technique is then to divide it into a number of sections, each stored in
231 a separate file, which you Include into a short master game file. For
234 .. code-block:: inform
236 !============================================================================
237 Constant Story "War and Peace";
239 "^An extended Inform example
240 ^by me and Leo Tolstoy.^";
255 !============================================================================
261 When you run the compiler you can set some optional controls; these are
262 called *switches* because most of them are either on or off (although a
263 few accept a numeric value 0–9). Switches affect compilation in a
264 variety of ways, often just by changing the information displayed by the
265 compiler when it’s running. A typical command line (although this may
266 vary between machines) would be:
268 :samp:`inform {source_file story_file switches}`
270 where "``inform``" is the name of the compiler, the
271 :samp:`{story_file}` is optional (so that you can specify a different
273 :samp:`{source_file}`) and the switches are also optional. Note that
274 switches must be preceded by a hyphen ``-``; if you want to set, for
275 instance, Strict mode, you'd write ``-S`` , while if you want to
276 deactivate it, you’d write ``-~S``. The tilde sign can, as elsewhere, be
277 understood as "not". If you wish to set many switches, just write them
278 one after another separated by spaces and each with its own hyphen, or
279 merge them with one hyphen and no spaces:
281 :samp:`inform MyGame.inf -S -s -X`
283 :samp:`inform MyGame.inf -Ssx`
285 Although there's nothing wrong with this method, it isn't awfully
286 convenient should you need to change the switch settings. A more
287 flexible method is to define the switches at the very start of your
288 source file, again in either format:
294 Normally, all switches are off by default, except Strict mode (``-S``),
295 which is on and checks the code for additional mistakes. It's well worth
296 adding Debug mode (``-D``), thus making the debugging verbs available at
297 run time. This is the ideal setting while coding, but you should turn
298 Debug mode off (just remove the ``-D``) when you release your game to
299 the public. This is fortunately very easy to check, since the game
300 banner ends with the letter "D" if the game was compiled in Debug mode:
302 .. code-block:: transcript
305 A simple Inform example
306 by Roger Firth and Sonja Kesserich.
307 Release 3 / Serial number 040804 / Inform v6.30 Library 6/11 SD
309 Switches are case sensitive, so you get different effects from ``-x``
310 and ``-X``. Some of the more useful switches are:
313 Set compiler Strict mode off. This deactivates some additional error
314 checking features when it reads your source file. Strict mode is on by
318 Compile to this version of story file. Versions 5 (on by default) and
319 8 are the only ones you should ever care about; they produce,
320 respectively, story files with the extensions .z5 and .z8 . Version 5
321 was the Advanced Infocom design, and is the default produced by
322 Inform. This is the version you'll normally be using, which allows
323 file sizes up to 256 Kbytes. If your game grows beyond that size,
324 you'll need to compile to the Version 8 story file, which is very
325 similar to Version 5 but allows a 512 Kbytes file size.
328 Include respectively the debugging verbs and the Infix debugger in the
329 story file (see "Debugging your game" on page 197).
332 Display help information about the compiler. ``-h1`` produces
333 information about file naming, and ``-h2`` about the available
337 ``-n`` displays the number of declared attributes, properties and
338 actions. ``-j`` lists objects as they are being read and constructed
342 Offer game statistics. This provides a lot of information about your
343 game, including the number of objects, verbs, dictionary entries,
344 memory usage, etc., while at the same time indicating the maximum
345 allowed for each entry. This can be useful to check whether you are
346 nearing the limits of Inform.
349 Record all the text of the game into a temporary file, useful to check
350 all your descriptions and messages by running them through a spelling
353 If you run the compiler with the ``-h2`` switch, you’ll find that there
354 are many more switches than these, offering mostly advanced or obscure
355 features which we consider to be of little interest to beginners.
356 However, feel free to try whatever switches catch your eye; nothing you
357 try here will affect your source file, which is strictly read-only as
358 far as the compiler is concerned.