1 ============================
2 William Tell: in his prime
3 ============================
9 | |CENTER| *O was an oyster girl, and went about town;*
10 | |CENTER| *P was a parson, and wore a black gown.*
14 .. image:: /images/picO.png
17 |O|\ur game's action nears its climax in the town's central square. In
18 this chapter we define the square's constituent rooms and deal with
19 Wilhelm's approach to the hat on the pole -- does he salute it, or does he
20 remain proudly defiant?
24 The south side of the square
25 ============================
27 The town square, notionally one enormous open space, is represented by
28 three rooms. Here's the south side::
30 Room south_square "South side of the square"
32 "The narrow street to the south has opened onto the town square,
33 and resumes at the far side of this cobbled meeting place.
34 To continue along the street towards your destination --
35 Johansson's tannery -- you must walk north across the square,
36 in the middle of which you see Gessler's hat set on that
37 loathsome pole. If you go on, there's no way you can avoid
38 passing it. Imperial soldiers jostle rudely through the throng,
39 pushing, kicking and swearing loudly.",
44 with name 'hat' 'pole',
47 print_ret "You're too far away at the moment.";
49 found_in south_square north_square;
51 Prop "Gessler's soldiers"
52 with name 'soldier' 'soldiers' 'guard' 'guards',
53 description "They're uncouth, violent men, not from around here.",
56 print_ret "You're outnumbered many times.";
58 print_ret "Such scum are beneath your contempt.";
60 found_in south_square mid_square north_square marketplace,
61 has animate pluralname proper;
63 It's all pretty standard stuff: just a ``Room`` and two ``Prop``\s. The
64 "real" pole object is located in the ``mid_square`` room, which means that
65 players can't EXAMINE it from this room (technically, it's "not in scope").
66 However, since we're pretending that Wilhelm can see the whole of the
67 square from where he's standing, we need to provide a dummy hat on a pole,
68 ``found_in`` both this room and the north side of the square, even if it's
69 "too far away" for a detailed description.
71 In fact, it's "too far away" for anything. We've replaced the standard
72 ``before`` action for the ``Prop`` class (which permits ``Examine``, but
73 rejects other actions with "You don't need to worry about...") with one
74 rejecting *all* actions. Since Wilhelm's hatred of the vogt's activities
75 is central to our plot, a message saying "You don't need to worry about the
76 hat" would be unacceptably misleading.
78 The obnoxious soldiers are also implemented very sketchily; they need to be
79 there, but they don't do much. Their most interesting characteristic is
80 probably that they trap two actions -- ``FireAt`` and ``Talk`` -- which are
81 *not* part of the library, but instead new actions that we've defined
82 specially for this game. We'll talk about those actions in :ref:`verbs`,
83 at which time the role of this ``before`` property will make more sense.
85 The middle of the square
86 ========================
88 The activities here are pivotal to the game's plot. Wilhelm has arrived
89 from the south side of the square, and now encounters the pole with the hat
90 on top. He can do three things:
92 #. Return south. That's allowed, but all it does is waste a little time --
93 there's nothing else to usefully do south of here.
95 #. Salute the pole, and then proceed to the north. That's allowed, though
96 it rather subverts the folk story.
98 #. Attempt to proceed northwards without saluting the pole. Twice, a
99 soldier will prevent this, and issue a verbal warning. On the third
100 attempt, patience runs out, and Wilhelm is hauled off to perform his
103 So, there are two actions that we need to look out for: ``Salute`` (trapped
104 by the pole), and ``Go`` (which can be trapped by the room itself). ``Go``
105 is a standard library action. ``Salute`` is one that we've devised; let's
106 deal with it first. Here's a first cut of the room::
108 Room mid_square "Middle of the square"
110 "There is less of a crush in the middle of the square; most
111 people prefer to keep as far away as possible from the pole
112 which towers here, topped with that absurd ceremonial hat. A
113 group of soldiers stands nearby, watching everyone who passes.",
119 Furniture pole "hat on a pole" mid_square
120 with name 'wooden' 'pole' 'pine' 'hat' 'black' 'red' 'brim' 'feathers',
122 "The pole, the trunk of a small pine some few inches in diameter,
123 stands about nine or ten feet high. Set carefully on top is
124 Gessler's ludicrous black and red leather hat, with a widely
125 curving brim and a cluster of dyed goose feathers.",
126 has_been_saluted false,
129 print_ret "Tempting, but you're not looking for trouble.";
131 self.has_been_saluted = true;
132 print_ret "You salute the hat on the pole. ^^
133 ~Why, thank you, sir,~ sneers the soldier.";
137 The room will need some more work in a minute, but the pole object is
138 complete (note that we've simplified matters slightly by making one object
139 represent both the pole and the hat which it supports). It mentions a
140 property which we've not met before: ``has_been_saluted``. What a
141 remarkable coincidence: the library provides a property with a name that's
142 exactly right for our game; surely not?
144 No, of course not. ``has_been_saluted`` isn't a standard library property;
145 it's one that we've just invented. Notice how easily we did it -- we
146 simply included the line::
148 has_been_saluted false,
150 in the object definition and voilĂ , we've added our own home-made property,
151 and initialised it to ``false``. To switch the state of the property, we
154 pole.has_been_saluted = true;
155 pole.has_been_saluted = false;
157 or just (within the pole object)::
159 self.has_been_saluted = true;
160 self.has_been_saluted = false;
162 We could also test, if necessary, how the property currently fares::
164 if (pole.has_been_saluted == true) ...
166 and that is exactly what we'll be doing in a minute to check whether
167 Wilhelm has saluted the pole, and choose between different outcomes.
169 Notice that we use ``==`` (that's two equals signs) to test for "is equal
170 to"; don't confuse this usage with ``=`` (a single equals sign) which
171 assigns a value to a variable. Compare these examples:
183 * - assigns the value 10 to ``score``
184 - does nothing; ``score`` is unchanged
186 * - ``if (score == 10) ...``
187 - ``if (score = 10) ...``
189 * - executes the next statement only if the value of ``score`` is 10
190 - assigns 10 to ``score``, then always executes the next statement --
191 because ``score = 10`` evaluates to 10, which is treated as
192 ``true``, so the test is always ``true``
194 Defining a new property variable which, instead of applying to every object
195 in the game (as do the standard library properties), is specific only to a
196 class of objects or even -- as here -- to a single object, is a common and
197 powerful technique. In this game, we need a ``true/false`` variable to
198 show whether Wilhelm has saluted the pole or not: the clearest way is to
199 create one as part of the pole. So, when the pole object traps the Salute
200 action, we do two things: use a ``self.has_been_saluted = true`` statement
201 to record the fact, and then use a ``print_ret`` statement to tell players
202 that the salute was "gratefully" received.
206 Creating new property variables like this -- at the drop of a hat, as it
207 were -- is the recommended approach, but it isn't the only possibility.
208 We briefly mention some alternative approaches in
209 :ref:`reading-other-code`.
211 Back to the ``mid_square`` room. We've said that we need to detect Wilhelm
212 trying to leave this room, which we can do by trapping the ``Go`` action in
213 a ``before`` property. Let's sketch the coding we'll need::
217 if (noun == s_obj) { Wilhelm is trying to move south }
218 if (noun == n_obj) { Wilhelm is trying to move north }
221 We can easily trap the ``Go`` action, but which direction is he moving?
222 Well, it turns out that the interpreter turns a command of GO SOUTH (or
223 just SOUTH) into an action of ``Go`` applied to an object ``s_obj``. This
224 object is defined by the library; so why isn't it called just "``south``"?
225 Well, because we already have another kind of south, the property ``s_to``
226 used to say what lies in a southerly direction when defining a room. To
227 avoid confusing them, ``s_to`` means "south to" and ``s_obj`` means "south
228 when the player types it as the object of a verb".
230 The identity of the object which is the target of the current action is
231 stored in the ``noun`` variable, so we can write the statement ``if (noun
232 == s_obj)`` to test whether the contents of the ``noun`` variable are equal
233 to the ID of the ``s_obj`` object -- and, if so, Wilhelm is trying to move
234 south. Another similar statement tests whether he's trying to move north,
235 and that's all that we're interested in; we can let other movements take
238 The words :samp:`{Wilhelm is trying to move south}` aren't part of our
239 game; they're just a temporary reminder that, if we need to execute any
240 statements in this situation, here's the place to put them. Actually,
241 that's the simpler case; it's when :samp:`{Wilhelm is trying to move
242 north}` that the fun starts. We need to behave in one of two ways,
243 depending on whether or not he's saluted the pole. But we *know* when he's
244 done that; the pole's ``has_been_saluted`` property tells us. So we can
245 expand our sketch like this::
249 if (noun == s_obj) { Wilhelm is trying to move south [1] }
250 if (noun == n_obj) { Wilhelm is trying to move north...
251 if (pole.has_been_saluted == true)
252 { ...and he's saluted the pole [2] }
253 else { ...but he hasn't saluted the pole [3] }
257 Here we have one ``if`` statement nested inside another. And there's more:
258 the inner ``if`` has an ``else`` clause, meaning that we can execute one
259 statement block when the test ``if (pole.has_been_saluted == true)`` is
260 true, and an alternative block when the test isn't true. Read that again
261 carefully, checking how the braces ``{...}`` pair up; it's quite complex,
262 and you need to understand what's going on. One important point to
263 remember is that, unless you insert braces to change this, an ``else``
264 clause always pairs with the most recent ``if``. Compare these two
268 if (condition2) { here when condition1 is true and condition2 is true }
269 else { here when condition1 is true and condition2 is false }
273 if (condition2) { here when condition1 is true and condition2 is true }
275 else { here when condition1 is false }
277 In the first example, the ``else`` pairs with the most recent :samp:`if
278 ({condition2})`, whereas in the second example the revised positioning of
279 the braces causes the ``else`` to pair with the earlier :samp:`if
284 We've used indentation as a visual guide to how the ``if`` and ``else``
285 are related. Be careful, though; the compiler matches an ``else`` to
286 its ``if`` purely on the basis of logical grouping, regardless of how
287 you've laid out the code.
289 Back to the before property. You should be able to see that the cases
290 marked ``[1]``, ``[2]`` and ``[3]`` correspond to the three possible
291 courses of action we listed at the start of this section. Let's write the
292 code for those, one at a time.
294 .. rubric:: Case 1: Returning south
296 First, :samp:`{Wilhelm is trying to move south}`; not very much to this::
298 warnings_count 0, ! for counting the soldier's warnings
302 self.warnings_count = 0;
303 pole.has_been_saluted = false;
306 if (pole.has_been_saluted == true)
307 { moving north...and he's saluted the pole }
308 else { moving north...but he hasn't saluted the pole }
312 Wilhelm might wander into the middle of the square, take one look at the
313 pole and promptly return south. Or, he might make one or two (but not
314 three) attempts to move north first, and then head south. *Or*, he might
315 be really perverse, salute the pole and only then head south. In all of
316 these cases, we take him back to square one, as though he'd received no
317 soldier's warnings (irrespective of how many he'd actually had) and as
318 though the pole had not been saluted (irrespective of whether it was or
319 not). In effect, we're pretending that the soldier has such a short
320 memory, he'll completely forget Wilhelm if our hero should move away from
323 To do all this, we've added a new property and two statements. The
324 property is ``warnings_count``, and its value will count how many times
325 Wilhelm has tried to go north without saluting the pole: 0 initially, 1
326 after his first warning, 2 after his second warning, 3 when the soldier's
327 patience finally runs out. The property ``warnings_count`` isn't a
328 standard library property; like the pole's ``has_been_saluted`` property,
329 it's one that we've created to meet a specific need.
331 Our first statement is ``self.warnings_count = 0``, which resets the value
332 of the ``warnings_count`` property of the current object -- the
333 ``mid_square`` room -- to 0. The second statement is
334 ``pole.has_been_saluted = false``, which signifies that the pole has not be
335 saluted. That's it: the soldier's memory is erased, and Wilhelm's actions
338 .. rubric:: Case 2: Moving north after saluting
340 :samp:`{Wilhelm is moving north...and he's saluted the pole}`; another easy
343 warnings_count 0, ! for counting the soldier's warnings
347 self.warnings_count = 0;
348 pole.has_been_saluted = false;
351 if (pole.has_been_saluted == true) {
352 print "^~Be sure to have a nice day.~^";
355 else { moving north...but he hasn't saluted the pole }
359 All that we need do is print a sarcastic goodbye from the soldier, and then
360 ``return false``. You'll remember that doing so tells the interpreter to
361 continue handling the action, which in this case is an attempt to move
362 north. Since this is a permitted connection, Wilhelm thus ends up in the
363 ``north_square`` room, defined shortly.
365 .. rubric:: Case 3: Moving north before saluting
367 So that just leaves the final case: :samp:`{moving north...but he hasn't
368 saluted the pole}`. This one has more to it than the others, because we
369 need the "three strikes and you're out" coding. Let's sketch a little
372 warnings_count 0, ! for counting the soldier's warnings
376 self.warnings_count = 0;
377 pole.has_been_saluted = false;
380 if (pole.has_been_saluted == true) {
381 print "^~Be sure to have a nice day.~^";
385 self.warnings_count = self.warnings_count + 1;
386 switch (self.warnings_count) {
387 1: First attempt at moving north
388 2: Second attempt at moving north
389 default: Final attempt at moving north
395 First of all, we need to count how many times he's tried to move north.
396 ``self.warnings_count`` is the variable containing his current tally, so we
397 add 1 to whatever value it contains: ``self.warnings_count =
398 self.warnings_count + 1``. Then, determined by the value of the variable,
399 we must decide what action to take: first attempt, second attempt, or final
400 confrontation. We could have used three separate ``if`` statements::
402 if (self.warnings_count == 1) { First attempt at moving north }
403 if (self.warnings_count == 2) { Second attempt at moving north }
404 if (self.warnings_count == 3) { Final attempt at moving north }
406 or a couple of nested ``if`` statements::
408 if (self.warnings_count == 1) { First attempt at moving north }
410 if (self.warnings_count == 2) { Second attempt at moving north }
411 else { Final attempt at moving north }
414 but for a series of tests all involving the same variable, a ``switch``
415 statement is usually a clearer way of achieving the same effect. The
416 generic syntax for a ``switch`` statement is::
418 switch (expression) {
419 value1: whatever happens when the expression evaluates to value1
420 value2: whatever happens when the expression evaluates to value2
422 valueN: whatever happens when the expression evaluates to valueN
423 default: whatever happens when the expression evaluates to something else
426 This means that, according to the current value of an expression, we can
427 get different outcomes. Remember that the :samp:`{expression}` may be a
428 ``Global`` or local variable, an object's property, one of the variables
429 defined in the library, or any other expression capable of having more than
430 one value. You could write ``switch (x)`` if ``x`` is a defined variable,
431 or even, for instance, ``switch (x+y)`` if both ``x`` and ``y`` are defined
432 variables. Those :samp:`{whatever happens when...}` are collections of
433 statements which implement the desired effect for a particular value of the
436 Although a switch statement :samp:`switch ({expression}) { ... }` needs
437 that one pair of braces, it doesn't need braces around each of the
438 individual "cases", no matter how many statements each of them includes.
439 As it happens, case 1 and case 2 contain only a single ``print_ret``
440 statement each, so we'll move swiftly past them to the third, more
441 interesting, case -- when ``self.warnings_count`` is 3. Again, we could
444 switch (self.warnings_count) {
445 1: First attempt at moving north
446 2: Second attempt at moving north
447 3: Final attempt at moving north
450 but using the word ``default`` -- meaning "any value not already catered
451 for" -- is better design practice; it's less likely to produce misleading
452 results if for some unforeseen reason the value of ``self.warnings_count``
453 isn't the 1, 2 or 3 you'd anticipated. Here's the remainder of the code
454 (with some of the printed text omitted)::
456 self.warnings_count = self.warnings_count + 1;
457 switch (self.warnings_count) {
462 style underline; print "Herr"; style roman;
463 print " Tell, now you're in real trouble. I asked you
465 old lime tree growing in the marketplace.^";
467 PlayerTo(marketplace);
471 The first part is really just displaying a lot of text, made slightly
472 messier because we're adding emphasis to the word "Herr" by using
473 underlining (which actually comes out as *italic type* on most
474 interpreters). Then, we make sure that Walter has the apple (just in case
475 we didn't give it to him earlier in the game), relocate to the final room
476 using ``PlayerTo(marketplace)``, and finally ``return true`` to tell the
477 interpreter that we've handled this part of the ``Go`` action ourselves.
478 And so, at long last, here's the complete code for the ``mid_square``, the
479 most complicated object in the whole game::
481 Room mid_square "Middle of the square"
483 "There is less of a crush in the middle of the square; most
484 people prefer to keep as far away as possible from the pole
485 which towers here, topped with that absurd ceremonial hat. A
486 group of soldiers stands nearby, watching everyone who passes.",
489 warnings_count 0, ! for counting the soldier's warnings
493 self.warnings_count = 0;
494 pole.has_been_saluted = false;
497 if (pole.has_been_saluted == true) {
498 print "^~Be sure to have a nice day.~^";
500 } ! end of (pole has_been_saluted)
502 self.warnings_count = self.warnings_count + 1;
503 switch (self.warnings_count) {
504 1: print_ret "A soldier bars your way. ^^
505 ~Oi, you, lofty; forgot yer manners, didn't you?
506 How's about a nice salute for the vogt's hat?~";
507 2: print_ret "^~I know you, Tell, yer a troublemaker,
508 ain't you? Well, we don't want no bovver here,
509 so just be a good boy and salute the friggin'
510 hat. Do it now: I ain't gonna ask you again...~";
513 style underline; print "Herr"; style roman;
514 print " Tell, now you're in real trouble. I asked you
515 nice, but you was too proud and too stupid. I
516 think it's time that the vogt had a little word
519 And with that the soldiers seize you and Walter
520 and, while the sergeant hurries off to fetch
521 Gessler, the rest drag you roughly towards the
522 old lime tree growing in the marketplace.^";
524 PlayerTo(marketplace);
527 } ! end of (pole has_NOT_been_saluted)
528 } ! end of (noun == n_obj)
531 The north side of the square
532 ============================
534 The only way to get here is by saluting the pole and then moving north; not
535 very likely, but good game design is about predicting the unpredictable. ::
537 Room north_square "North side of the square"
539 "A narrow street leads north from the cobbled square. In its
540 centre, a little way south, you catch a last glimpse of the pole
544 print_ret "With Walter at your side, you leave the square by the
545 north street, heading for Johansson's tannery.";
547 s_to "You hardly feel like going through all that again.";
549 There's one new feature in this room: the value of the ``n_to`` property is
550 a routine, which the interpreter runs when Wilhelm tries to exit the square
551 northwards. All that the routine does is set the value of the library
552 variable ``deadflag`` to 3, print a confirmation message, and ``return
553 true``, thus ending the action.
555 At this point, the interpreter notices that ``deadflag`` is no longer zero,
556 and terminates the game. In fact, the interpreter checks ``deadflag`` at
557 the end of every turn; these are the values that it's expecting to find:
559 * 0 -- this is the normal state; the game continues.
560 * 1 -- the game is over. The interpreter displays "You have died".
561 * 2 -- the game is over. The interpreter displays "You have won".
562 * any other value -- the game is over, but there aren't any appropriate
563 messages built into the library. Instead, the interpreter looks for an
564 :term:`entry point` routine called ``DeathMessage`` -- which we must
565 provide -- where we can define our own tailored "end messages".
567 In this game, we never set ``deadflag`` to 1, but we do use values of 2
568 and 3. So we'd better define a ``DeathMessage`` routine to tell players
571 [ DeathMessage; print "You have screwed up a favourite folk story"; ];
573 Our game has only one customised ending, so the simple ``DeathMessage``
574 routine we've written is sufficient for our purposes. Were you to conceive
575 multiple endings for a game, you could specify suitable messages by
576 checking for the current value of the ``deadflag`` variable::
579 if (deadflag == 3) print "You leave Scarlett O'Hara for good";
580 if (deadflag == 4) print "You crush Scarlett with a passionate embrace";
581 if (deadflag == 5) print "You've managed to divorce Scarlett";
585 Of course, you must assign the appropriate value to ``deadflag`` at the
586 point when the game arrives at each of those possible endings.
588 We've nearly finished. In the concluding chapter of this game, we'll talk
589 about the fateful shooting of the arrow.