18.4. Listing rules explicitly

| Chapter 18: Rulebooks |

| 18.4. Listing rules explicitly

If rules can manage perfectly well without, why bother to have names for rules?

The answer is that although Inform contains an elaborate mechanism for placing rules into the correct rulebook at the correct position, and this happens automatically, Inform will sometimes get it wrong. It will use a rule we do not want, or place them in an order which does not suit us. To put this right, we can give explicit instructions which take precedence over Inform's normal practice. This is done with the "to list" verb, as in the following examples.

1. The simplest usage is to place a named rule, which currently has no home, in any rulebook of our choice. (This looks redundant, but just occasionally we want the same rule to appear in two different rulebooks.)

> The blossom rule is listed in the every turn rules.

A rule can appear in more than one rulebook, but within any single rulebook it can only appear once.

2. We can also specify that the rule needs to appear before, or after, some other named rule in the same rulebook:

> The collapsing bridge rule is listed before the moving doorways rule in the instead rules.

Instead of being placed in specificity order in the whole "instead" rulebook, the "collapsing bridge" rule would now be placed in specificity order only in the first half of the "instead" rulebook - the rules from the start up to (but not including) the "moving doorways" rule.

"Listed" sentences are obeyed by Inform in sequence, so if later ones issue instructions contradicting earlier ones, it's the later ones which win out. Thus if we say "A is listed before B in X" and then "B is listed before A in X", the result is that B comes before A.

3. We can specify that a rule needs to appear first or last in a given rulebook:

> The collapsing bridge rule is listed first in the instead rules.

Again, if we make several such instructions about the same rulebook then the most recent one wins: "A is listed first in X. B is listed first in X. C is listed first in X." causes rulebook X to begin C, B, A.

4. We can also substitute one rule for another:

> My darkness rule is listed instead of the can't act in the dark rule in the visibility rules.

If rule A is listed instead of rule B in rulebook X, and A was already a rule in rulebook X, then A will move from its previous position to occupy the place where B was, and B will disappear. (In particular rule A will not be duplicated, which would break the principle that no rule occurs twice in the same rulebook.)

5. And we can strike down existing rules, either specifically or in all their applications:

> The can't act in the dark rule is not listed in the visibility rules.
> The can't remove from people rule is not listed in any rulebook.

This does not actually destroy the rules in question: they could still, for instance, be put into another rulebook, or even be applied explicitly, as we shall see. But unless we take deliberate action to the contrary, un-listing a rule amounts to abolishing it forever. This is a little drastic, and we will see subtler ways to change the standard behaviour later in the chapter.

379
| Example Saint Eligius Adding a first look rule that comments on locations when we visit them for the first time, inserting text after objects are listed but before any "every turn" rules might occur. |
RB

A not-infrequent desire in IF is to provide a few lines of comment when the player first enters a new room, after the objects are described but before anything else (such as an every turn rule) can fire. The cleanest, most systematic solution is to add a rule to the carry out looking rulebook, so: "Saint Eligius" The first look rule is listed after the room description paragraphs about objects rule in the carry out looking rules. A room can be commented or uncommented. A room is usually uncommented. This is the first look rule: if the location is uncommented, carry out the gawking at activity with the location. Gawking at something is an activity. Rule for gawking at the Diamond Market: say "Your throat closes and your eyes begin to sting. You have long disdained pomp and luxury, and railed against the oppression that brings such wealth to some men at the cost of the lives of others; you were not prepared for the magnificence." After gawking at a room (called the target): now the target is commented. And now the scene itself: The Cobbled Alley is a room. "The Alley has never been made into a proper street: the buildings on either side are simply too important to tear down. For all that, there isn't much sign of the magnificence nearby. The entrance you seek is set below street level, four grimy steps down to a half-basement." After going to Diamond Market: say "You descend the steps quickly and step into the small foyer, allowing yourself to be searched for weapons, before going on to..."; continue the action. Diamond Market is down from Cobbled Alley. "The roof is vaulted and painted in allegorical images representing Plenty, the Riches of the Earth, and Saint Eligius, patron of goldsmiths and jewelers. Under their watchful eye, dozens of men in sober black robes sit; and on the tables before them are rubies, emeralds, sapphires from oversea, but most of all diamonds, both raw and cut." The burly guard is a man in Diamond Market. "A burly guard patrols quite close to you, but even he is more sumptuously dressed than the average burly guard, and his buttons shine." Test me with "d / look".

380
| Example Verbosity 2 Making rooms give full descriptions each time we enter, even if we have visited before, and disallowing player use of BRIEF and SUPERBRIEF. |
RB

381
| Example Slouching A system of postures allowing the player and other characters to sit, stand, or lie down explicitly or implicitly on a variety of enterable supporters or containers, or in location. |
RB

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