Rulebooks contents
Latest Rule Result.
This used to be a large data structure which kept track of the effect of procedural rules, but in January 2011 procedurals were abolished. It retains only one purpose: as a place to record the result of the most recently completed rule. This used to sit on the top of the stack, and is now the only thing which ever sits on it. So the "stack" has just one 3-word record now. The meanings of these are as follows. The first word is one of the following:
(1) RS_SUCCEEDS indicates that the most recent rule or rulebook processed ended in success. Word 2 is false if there's no value, or the kind if there is, in which case word 3 contains the value itself. (2) RS_FAILS is similar, but for a failure. Note that failures can also return values. (3) RS_NEITHER is similar except that it cannot return any value, so that words 2 and 3 are meaningless.
25Constant RS_NEITHER = 0;
26Constant RS_SUCCEEDS = 1;
27Constant RS_FAILS = 2;
28
29Array latest_rule_result --> 3;
30
31[ RecordRuleOutcome usage rule1 rule2;
32 if ((latest_rule_result-->0 == RS_SUCCEEDS or RS_FAILS) &&
33 (KOVIsBlockValue(latest_rule_result-->1)))
34 BlkValueFree(latest_rule_result-->2);
35 if ((usage == RS_SUCCEEDS or RS_FAILS) && (KOVIsBlockValue(rule1)))
36 rule2 = BlkValueCopy(BlkValueCreate(rule1), rule2);
37 latest_rule_result-->0 = usage;
38 latest_rule_result-->1 = rule1;
39 latest_rule_result-->2 = rule2;
40];
Following.
Until January 2011, there were two ways to invoke a rulebook: to "follow" it or simply "process" it. With the demise of procedural rules, these became equivalent.
In the early days of Inform 7, stack usage became a serious issue since some forms of the Frotz Z-machine interpreter provided only 4K of stack by default. ("Only" 4K. In the mid-1980s, one of the obstacles facing IF authors at Infocom was the need to get the stack usage down to fewer than 600 bytes in order that the story file could be run on the smaller home computers of the day.) FollowRulebook was the major consumer of stack space, on average, because of its frequent recursion. Now that the process is simpler, this has become less problematic, since the routine now has fewer local variables.
FollowRulebook takes three arguments, of which only the first is compulsory:
(a) The rulebook is an I7 value of kind "rule", which means it can be either the ID number of a rulebook – from 0 up to N-1, where N is the number of rulebooks compiled by Inform, typically about 600 – or else the address of a routine representing an individual rule. (b) The parameter supplied to the rulebook. Much as arguments can be supplied to a function in a conventional language's function call, so a parameter can be supplied whenever a rulebook is invoked. (c) no_paragraph_skips is a flag: if explicitly set true, then the rulebook is run with paragraph breaking suppressed. This is the process by which paragraph division points are placed between rules, so that if two rules both print text then a paragraph break appears between. While that is appropriate for rulebooks attached to actions or for "every turn" rules, it is disastrous for rulebooks attached to activities such as "printing the name of something".
FollowRulebook returns R if rule R in the rulebook (or rule) chose to "succeed" or "fail", and false if it made no choice. (To repeat: if the rule explicitly fails, then FollowRulebook returns true. It's easy to write plausible-looking code which goes wrong because it assumes that the return value is success vs. failure.) The outcome of FollowRulebook is stored as described above: thus the most recent rule or rulebook succeeded or failed if –
(latest_rule_result-->0 == RS_SUCCEEDS)
(latest_rule_result-->0 == RS_FAILS)
and otherwise there was no decision.
89Global process_rulebook_count;
90Global debugging_rules = false;
91
92[ FollowRulebook rulebook parameter no_paragraph_skips
93 rv ss spv;
94 ss = self;
95 if ((Protect_I7_Arrays-->0 ~= 16339) || (Protect_I7_Arrays-->1 ~= 12345)) {
96 print "^^*** Fatal programming error: I7 arrays corrupted ***^^";
97 @quit;
98 }
99 if (parameter) { self = parameter; parameter_object = parameter; }
100 spv = parameter_value; parameter_value = parameter;
101
102 parameter = debugging_rules;
103 #ifndef MEMORY_ECONOMY;
104 if (debugging_rules) {
105 DebugRulebooks(rulebook, parameter);
106 process_rulebook_count = process_rulebook_count + debugging_rules;
107 }
108 #endif;
109 if ((rulebook >= 0) && (rulebook < NUMBER_RULEBOOKS_CREATED)) {
110 rv = rulebooks_array-->rulebook;
111 if (rv ~= EMPTY_RULEBOOK) {
112 if (rulebook ~= ACTION_PROCESSING_RB) MStack_CreateRBVars(rulebook);
113 if (say__p) RulebookParBreak(no_paragraph_skips);
114 rv = rv(no_paragraph_skips);
115 if (rulebook ~= ACTION_PROCESSING_RB) MStack_DestroyRBVars(rulebook);
116 } else {
117 rv = 0;
118 }
119 } else {
120 if (say__p) RulebookParBreak(no_paragraph_skips);
121 rv = indirect(rulebook);
122 if (rv == 2) rv = reason_the_action_failed;
123 else if (rv) rv = rulebook;
124 }
125 if (rv) {
126 #ifndef MEMORY_ECONOMY;
127 if (debugging_rules) {
128 process_rulebook_count = process_rulebook_count - debugging_rules;
129 if (process_rulebook_count < 0) process_rulebook_count = 0;
130 spaces(2*process_rulebook_count);
131 if (latest_rule_result-->0 == RS_SUCCEEDS) print "[stopped: success]^";
132 if (latest_rule_result-->0 == RS_FAILS) print "[stopped: fail]^";
133 }
134 #endif;
135 } else {
136 if (debugging_rules)
137 process_rulebook_count = process_rulebook_count - debugging_rules;
138 latest_rule_result-->0 = RS_NEITHER;
139 }
140 debugging_rules = parameter;
141 self = ss; parameter_value = spv;
142 return rv;
143];
144
145[ RulebookParBreak no_paragraph_skips;
146 if ((no_paragraph_skips == false) && (say__pc & PARA_NORULEBOOKBREAKS == 0))
147 DivideParagraphPoint();
148];
Specifying Outcomes.
The following provide ways for rules to succeed, fail or decline to do either.
SetRulebookOutcome is a little different: it changes the outcome state of the most recent rule completed, not the current one. (It's used only when saving and restoring this in the actions machinery: rules should not call it.)
160[ ActRulebookSucceeds rule_id;
161 if (rule_id) reason_the_action_failed = rule_id;
162 RulebookSucceeds();
163];
164
165[ ActRulebookFails rule_id;
166 if (rule_id) reason_the_action_failed = rule_id;
167 RulebookFails();
168];
169
170[ RulebookSucceeds weak_kind value;
171 RecordRuleOutcome(RS_SUCCEEDS, weak_kind, value);
172];
173
174[ RulebookFails weak_kind value;
175 RecordRuleOutcome(RS_FAILS, weak_kind, value);
176];
177
178[ RuleHasNoOutcome;
179 RecordRuleOutcome(RS_NEITHER, 0, 0);
180];
181
182[ SetRulebookOutcome a;
183 latest_rule_result-->0 = a;
184];
Discovering Outcomes.
And here is how to tell what the results were.
190[ RulebookOutcome a;
191 a = latest_rule_result-->0;
192 if ((a == RS_FAILS) || (a == RS_SUCCEEDS)) return a;
193 return RS_NEITHER;
194];
195
196[ RulebookFailed;
197 if (latest_rule_result-->0 == RS_FAILS) rtrue; rfalse;
198];
199
200[ RulebookSucceeded;
201 if (latest_rule_result-->0 == RS_SUCCEEDS) rtrue; rfalse;
202];
203
204[ ResultOfRule RB V F K a;
205 if (RB) FollowRulebook(RB, V, F);
206 a = latest_rule_result-->0;
207 if ((a == RS_FAILS) || (a == RS_SUCCEEDS)) {
208 a = latest_rule_result-->1;
209 if (a) return latest_rule_result-->2;
210 }
211 if (K) return DefaultValueOfKOV(K);
212 return 0;
213];
Printing Rule Names.
This is the I6 printing rule used for a value of kind "rule", which as noted above can either be rulebook ID numbers in the range 0 to N-1 or are addresses of individual rules.
Names of rules and rulebooks take up a fair amount of space, and one of the main memory economies enforced by the "Use memory economy" option is to omit the necessary arrays. (It's not the text which is the problem so much as the table of addresses pointing to that text, which has to live in precious readable memory on the Z-machine.)
227#IFNDEF MEMORY_ECONOMY;
228{-array:Phrases::Manager::RulebookNames}
229#ENDIF;
230
231[ RulePrintingRule R p1;
232#ifndef MEMORY_ECONOMY;
233 if ((R>=0) && (R<NUMBER_RULEBOOKS_CREATED)) {
234 print (string) (RulebookNames-->R);
235 } else {
236{-call:Phrases::Manager::compile_rule_printing_switch}
237 print "(nameless rule at address ", R, ")";
238 }
239#ifnot;
240 if ((R>=0) && (R<NUMBER_RULEBOOKS_CREATED)) {
241 print "(rulebook ", R, ")";
242 } else {
243 print "(rule at address ", R, ")";
244 }
245#endif;
246];
Casting.
Nothing needs to be done to a rulebook value to make it a rule value.
252[ RULEBOOK_TY_to_RULE_TY r;
253 return r;
254];
Debugging.
Two modest routines to print out the names of rules and rulebooks when they occur, in so far as memory economy allows this.
261[ DebugRulebooks subs parameter i;
262 spaces(2*process_rulebook_count);
263 print "[", (RulePrintingRule) subs;
264 if (parameter) print " / on O", parameter;
265 print "]^";
266];
267
268[ DB_Rule R N blocked;
269 if (R==0) return;
270 print "[Rule ~", (RulePrintingRule) R, "~ ";
271 #ifdef NUMBERED_RULES; print "(", N, ") "; #endif;
272 if (blocked == false) "applies.]";
273 print "does not apply (wrong ", (address) blocked, ").]^";
274];