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2 Appendix C -- "William Tell" story
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5 .. highlight:: transcript
9 .. image:: /images/picW.png
12 |W|\illiam Tell, our second game, is also very straightforward. See
13 "William Tell: a tale is born" on page 69, "William Tell: the early years"
14 on page 79, "William Tell: in his prime" on page 91 and "William Tell: the
15 end is nigh" on page 103.
20 .. literalinclude:: /examples/Tell.txt
26 .. literalinclude:: /examples/Tell.inf
29 .. _compile-as-you-go:
34 Your understanding of how the "William Tell" game works will be
35 considerably enhanced if you type in the code for yourself as you read
36 through the guide. However, it takes us four chapters to describe the
37 game, which isn't complete and playable until the end of Chapter 9. Even
38 if you make no mistakes in your typing, the game won't compile without
39 errors before that point, because of references in earlier chapters to
40 objects which aren't presented until later chapters (for example,
41 Chapter 6 mentions the ``bow`` and ``quiver`` objects, but we don't
42 define them until Chapter 7). This is a bit of a nuisance, because as a
43 general rule we advise you to compile frequently -- more or less after
44 every change you make to a game -- in order to detect syntax and
45 spelling mistakes as soon as possible.
47 Fortunately, there's a fairly easy way round the difficulty, though it
48 involves a little bit of cheating. The trick is temporarily to add
49 minimal definitions -- often called "stubs" -- of the objects whose full
50 definitions have yet to be provided.
52 For example, if you try to compile the game in the state that it's
53 reached by the end of Chapter 6, you’ll get this::
55 Tell.inf(16): Warning: Class "Room" declared but not used
56 Tell.inf(19): Warning: Class "Prop" declared but not used
57 Tell.inf(27): Warning: Class "Furniture" declared but not used
58 Tell.inf(44): Error: No such constant as "street"
59 Tell.inf(46): Error: No such constant as "bow"
60 Tell.inf(47): Error: No such constant as "quiver"
61 Compiled with 3 errors and 3 warnings
63 However, by adding these lines to the end of your game file:
65 .. code-block:: inform
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``
106 .. code-block:: inform
109 with description "UNDER CONSTRUCTION",
112 By doing this, we ensure that *every* room has a description of some
113 form; normally we'd override this default value with something
114 meaningful -- "The narrow street runs north towards the town square..."
115 and so on -- by including a ``description`` property in the object's
116 definition. However, in a stub object used only for testing, a default
117 description is sufficient (and less trouble)::
120 A simple Inform example
121 by Roger Firth and Sonja Kesserich.
122 Release 3 / Serial number 040804 / Inform v6.30 Library 6/11 SD
129 a (quiver) (being worn)
133 You can't see any such thing.
137 You'll notice a couple of interesting points. Because we didn't supply
138 external names with our ``street`` , ``bow`` and ``quiver`` stubs, the
139 compiler has provided some for us -- ``(street)`` , ``(bow)`` and
140 ``(quiver)`` -- simply by adding parentheses around the internal IDs
141 which we used. And, because our ``bow`` and ``quiver`` stubs have no
142 ``name`` properties, we can't actually refer to those objects when
143 playing the game. Neither of these points would be acceptable in a
144 finished game, but for testing purposes at this early stage -- they'll
147 So far, we've seen how the addition of three temporary object
148 definitions enables us to compile the incomplete game, in its state at
149 the end of Chapter 6. But once we reach the end of Chapter 7, things
150 have moved on, and we now need a different set of stub objects. For a
151 test compilation at this point, remove the previous set of stubs, and
152 instead add these -- ``south_square`` and ``apple`` objects, and a dummy
153 action handler to satisfy the ``Talk`` action in Helga’s life property:
155 .. code-block:: inform
157 ! ===============================================================
158 ! TEMPORARY DEFINITIONS NEEDED TO COMPILE AT THE END OF CHAPTER 7
165 Similarly, at the end of Chapter 8, replace the previous stubs by these
166 if you wish to check that the game compiles:
168 .. code-block:: inform
170 ! ===============================================================
171 ! TEMPORARY DEFINITIONS NEEDED TO COMPILE AT THE END OF CHAPTER 8
180 Finally, by the end of Chapter 9 the game is complete, so you can delete
181 the stubs altogether.
183 Used with care, this technique of creating a few minimal stub objects
184 can be convenient -- it enables you to "sketch" a portion of your game
185 in outline form, and to compile and test the game in that state, without
186 needing to create complete object definitions. However, you've got very
187 little interaction with your stubs, so don't create too many of them.
188 And of course, never forget to flesh out the stubs into full definitions