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Start of Chapter 7: Basic Actions |
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Back to §7.2. Instead rules |
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Onward to §7.4. Try and try silently |
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§7.3. Before rules
Despite what was said in the previous section, instead rules do not quite bypass all of the usual rules. Inform knows that certain actions require light: for instance,
examining the napkin; looking; looking under the dining table
and if it is dark then none of these actions will be allowed, and any instead rules about them will not even be reached. Similarly, Inform knows that most actions require physical access to their objects: so "taking the napkin" would be blocked if the napkin were, say, inside a closed glass bottle, whereas "examining the napkin" would not. So an instead rule can only take effect if the action has already passed these basic reasonability tests.
"Before" rules genuinely precede checking of any kind. They also differ from instead rules in that they do not automatically stop the action in its tracks. Rather, they are provided as an opportunity to ensure that something else is done first. For example:
Before taking the napkin, say "(first unfolding its delicate origami swan)".
whence
>GET NAPKIN
(first unfolding its delicate origami swan)
Taken.
We have seen that instead rules automatically stop actions, whereas before rules automatically allow them to continue. We sometimes want to change this. The magic word "instead" can therefore be tacked on to any instruction in a before rule, and will have the effect of immediately stopping the action at that instruction. Thus the following two rules are (almost) equivalent:
Before taking the key, instead say "It seems to be soldered to the keyhole."
Instead of taking the key, say "It seems to be soldered to the keyhole."
It is also possible to be explicit about stopping the action:
stop the action
This phrase stops the current rule, stops the rulebook being worked through, and finally stops the action being processed. Example:
Before taking the key:
say "It seems to be soldered to the keyhole.";
stop the action.
Finally, we can prevent Inform from stopping the action when it otherwise might:
continue the action
This phrase ends the current rule, but in a way which keeps its rulebook going, so that the action being processed will carry on rather than being stopped. Example:
Instead of taking the napkin:
say "(first unfolding its delicate origami swan)[command clarification break]";
continue the action.
An "instead" rule ordinarily stops the action when it finishes, so the "continue the action" is needed to make things carry on. (This rule would have been better written as a "before" rule, in fact, but it shows the idea.)
As a general principle, it is good style to use instead rules whenever blocking actions, and before rules only when it is genuinely necessary to do something first but then to continue: in fact, it is good style to use "stop the action" or "continue the action" as little as possible.
