18.10. Success and failure

| Chapter 18: Rulebooks |

| 18.10. Success and failure

Though we have blurred over this point so far, each rule must ordinarily end with one of three outcomes: success, failure and neither ("no outcome").

When a rulebook is followed, what happens is that each of its rules is followed in turn until one of them ends in success or failure - if ever: it is possible that each rule is tried and each ends with no outcome, so that the rulebook simply runs out of rules to try.

For some rulebooks, these are not useful ideas: "every turn" rules, for instance, never produce an outcome, which is why the "every turn" rulebook always runs through all its rules at the end of each turn. But for other rulebooks, such as "check taking", it's important that a rule which fails will stop the whole rulebook. For instance, we might find that the "can't take yourself rule" produces no outcome (because we aren't trying to do that), and then likewise the "can't take other people rule" (ditto) but that the "can't take component parts rule" prints up a complaint, and fails the action: the rulebook stops, and never goes on to (for instance) the "can't take scenery rule". This is good, because an impossible action often fails for several reasons at once, and we only want to print up one objection, not a whole list.

To follow the working of this mechanism, we need to be able to predict the outcome of any given rule. Sometimes this is easy to spot. For instance, in a rule which works on actions:

> continue the action; means "end this rule with no outcome"
> stop the action; means "end this rule in failure"
> ... instead; means "end this rule in failure"

("Success" and "failure" are technical terms here: they do not mean that the player has or hasn't got what he wanted.) This is why the rule:

> Before taking something: say "The sentry won't let you!" instead.

ends in failure, and therefore stops the "before" rulebook. Another easy-to-spot case is when a rule makes use of the explicit phrases:

rule succeeds

This causes the current rule to end immediately, with its outcome considered to be a success. That means the rulebook being worked through will also end, and also be a success.

rule fails

This causes the current rule to end immediately, with its outcome considered to be a failure. That means the rulebook being worked through will also end, and also be a failure.

make no decision

This causes the current rule to end immediately, but with no outcome. That means the rulebook being worked through will continue to run on, beginning with the next rule.

But what happens if a rule simply doesn't say whether it succeeds, fails or has no outcome? In that case it depends on the rulebook. For almost all rulebooks, a rule which doesn't make a choice has no outcome, as in the following example:

> Before taking something: say "The sentry looks at you anxiously!"

This rule, if it takes effect, ends with no outcome - so the action continues. But other rulebooks have a different convention: the most important is "instead", where a rule making no explicit choice is deemed to end in failure. For instance:

> Instead of taking something: say "The sentry prods you with his rifle!"

This rule, if it takes effect, ends in failure and therefore stops the action.

We call this the default outcome of a rulebook. The default outcome of "before" (and of almost all rulebooks, in fact) is no outcome; the default outcome of "instead" is failure; the default outcome of "after" is success. The few exceptional cases with default outcome success or failure are marked as such in the Rules index.

When we create a rulebook, it will default to "no outcome". But we can specify otherwise with sentences like so:

> The cosmic analysis rules are a rulebook. The cosmic analysis rules have default failure.

Finally, note that the default outcome for a rulebook is really the default outcome for any rule in that rulebook: if no rules in the rulebook ever apply, for instance if there aren't any and the rulebook is empty, then the rulebook ends with no outcome at all.

We can test the latest outcome like so:

if rule succeeded:

This condition is true if the most recently followed rule ended in success. Example: follow the hypothetical clever rule; if rule succeeded: ...

if rule failed:

This condition is true if the most recently followed rule ended in failure. Example: follow the hypothetical clever rule; if rule failed: ... Note that this is not the opposite of "rule succeeded", because there's a third possibility: that it ended with no outcome.

386
| Example Feline Behavior A cat which reacts to whatever items it has handy, returning the result of a rulebook for further processing. |
RB

387
| Example Kyoto Expanding the effects of the THROW something AT something command so that objects do make contact with one another. |
RB

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