1 ======================================
2 Appendix C -- "William Tell" story
3 ======================================
7 .. image:: /images/picW.png
14 illiam Tell, our second game, is also very straightforward. See "William
15 Tell: a tale is born" on page 69, "William Tell: the early years" on
16 page 79, "William Tell: in his prime" on page 91 and "William Tell: the
17 end is nigh" on page 103.
22 .. literalinclude:: /examples/Tell.txt
28 .. literalinclude:: /examples/Tell.inf
31 .. _compile-as-you-go:
36 Your understanding of how the "William Tell" game works will be
37 considerably enhanced if you type in the code for yourself as you read
38 through the guide. However, it takes us four chapters to describe the
39 game, which isn't complete and playable until the end of Chapter 9. Even
40 if you make no mistakes in your typing, the game won't compile without
41 errors before that point, because of references in earlier chapters to
42 objects which aren't presented until later chapters (for example,
43 Chapter 6 mentions the ``bow`` and ``quiver`` objects, but we don't
44 define them until Chapter 7). This is a bit of a nuisance, because as a
45 general rule we advise you to compile frequently -- more or less after
46 every change you make to a game -- in order to detect syntax and
47 spelling mistakes as soon as possible.
49 Fortunately, there's a fairly easy way round the difficulty, though it
50 involves a little bit of cheating. The trick is temporarily to add
51 minimal definitions -- often called "stubs" -- of the objects whose full
52 definitions have yet to be provided.
54 For example, if you try to compile the game in the state that it's
55 reached by the end of Chapter 6, you’ll get this::
57 Tell.inf(16): Warning: Class "Room" declared but not used
58 Tell.inf(19): Warning: Class "Prop" declared but not used
59 Tell.inf(27): Warning: Class "Furniture" declared but not used
60 Tell.inf(44): Error: No such constant as "street"
61 Tell.inf(46): Error: No such constant as "bow"
62 Tell.inf(47): Error: No such constant as "quiver"
63 Compiled with 3 errors and 3 warnings
65 However, by adding these lines to the end of your game file::
67 ! ===============================================================
68 ! TEMPORARY DEFINITIONS NEEDED TO COMPILE AT THE END OF CHAPTER 6
74 a compilation should now give only this::
76 Tell.inf(19): Warning: Class "Prop" declared but not used
77 Tell.inf(27): Warning: Class "Furniture" declared but not used
78 Compiled with 2 warnings
80 That's a lot better. It's not worth worrying about those warnings, since
81 it's easy to understand where they come from; anyway, they'll go away
82 shortly. More important, there are no errors, which means that you've
83 probably not made any major typing mistakes. It also means that the
84 compiler has created a story file, so you can try "playing" the game. If
85 you do, though, you'll get this::
88 A simple Inform example
89 by Roger Firth and Sonja Kesserich.
90 Release 3 / Serial number 040804 / Inform v6.30 Library 6/11 SD
93 ** Library error 11 (27,0) **
94 ** The room "(street)" has no "description" property **
97 Whoops! We've fallen foul of Inform's rule saying that every room must
98 have a ``description`` property, to be displayed by the interpreter when
99 you enter that room. Our ``street`` stub hasn't got a ``description``,
100 so although the game compiles successfully, it still causes an error to
101 be reported at run-time.
103 The best way round this is to extend the definition of our ``Room``
107 with description "UNDER CONSTRUCTION",
110 By doing this, we ensure that *every* room has a description of some
111 form; normally we'd override this default value with something
112 meaningful -- "The narrow street runs north towards the town square..."
113 and so on -- by including a ``description`` property in the object's
114 definition. However, in a stub object used only for testing, a default
115 description is sufficient (and less trouble)::
118 A simple Inform example
119 by Roger Firth and Sonja Kesserich.
120 Release 3 / Serial number 040804 / Inform v6.30 Library 6/11 SD
127 a (quiver) (being worn)
131 You can't see any such thing.
135 You'll notice a couple of interesting points. Because we didn't supply
136 external names with our ``street`` , ``bow`` and ``quiver`` stubs, the
137 compiler has provided some for us -- ``(street)`` , ``(bow)`` and
138 ``(quiver)`` -- simply by adding parentheses around the internal IDs
139 which we used. And, because our ``bow`` and ``quiver`` stubs have no
140 ``name`` properties, we can't actually refer to those objects when
141 playing the game. Neither of these points would be acceptable in a
142 finished game, but for testing purposes at this early stage -- they'll
145 So far, we've seen how the addition of three temporary object
146 definitions enables us to compile the incomplete game, in its state at
147 the end of Chapter 6. But once we reach the end of Chapter 7, things
148 have moved on, and we now need a different set of stub objects. For a
149 test compilation at this point, remove the previous set of stubs, and
150 instead add these -- ``south_square`` and ``apple`` objects, and a dummy
151 action handler to satisfy the ``Talk`` action in Helga’s life property::
153 ! ===============================================================
154 ! TEMPORARY DEFINITIONS NEEDED TO COMPILE AT THE END OF CHAPTER 7
161 Similarly, at the end of Chapter 8, replace the previous stubs by these
162 if you wish to check that the game compiles::
164 ! ===============================================================
165 ! TEMPORARY DEFINITIONS NEEDED TO COMPILE AT THE END OF CHAPTER 8
174 Finally, by the end of Chapter 9 the game is complete, so you can delete
175 the stubs altogether.
177 Used with care, this technique of creating a few minimal stub objects
178 can be convenient -- it enables you to "sketch" a portion of your game
179 in outline form, and to compile and test the game in that state, without
180 needing to create complete object definitions. However, you've got very
181 little interaction with your stubs, so don't create too many of them.
182 And of course, never forget to flesh out the stubs into full definitions