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§12.9. Check, carry out, report
The normal behaviour of an action is specified by its three associated rulebooks - check, carry out and report. In the case of our "photographing" example, these rulebooks will be:
Check photographing. Here, for instance, we need to verify that the player has the camera. If any of our checks fail, we should say why and stop the action. If they succeed, we say nothing.
Carry out photographing. At this stage no further checking is needed (or allowed): the action now definitively takes place. At this point we might, for instance, deduct one from the number of exposures left on the film in the camera, or award the player points for capturing something interesting for posterity. But we should say nothing.
Report photographing. At this stage no further activity is needed (or allowed): whatever effect the action had, it has happened and is now over. All we can do is to say what has taken place.
So far we have not really gone into the business of what rulebooks are, and we don't do so here either - suffice to say that we can now create whatever rules we need:
A check photographing rule:
if the camera is not carried:
say "You can hardly photograph without a camera, now can you?" instead.
In fact, writing "a check photographing rule" is over-formal. We can more simply label our rules like so:
if we have photographed the noun:
say "You've already snapped [the noun]." instead.
Report photographing: say "Click!"
For the sake of brevity, photography has no interesting consequence (no points to be won, no film to use up), so there are no carry out rules here. Note the way we used the word "instead" once again to stop actions in their tracks.
We can continue to add rules at any point, and a classic thing that happens when testing a new work is that the designer realises there is a case which has not been thought of:
if the noun is the camera:
say "That would require some sort of contraption with mirrors." instead.
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The Dark Ages Revisited
This will be explored more in subsequent examples, but one of the things we can do with carry out rules is extend the function of existing commands so that they do more, or have special effects in specific situations. For instance, suppose we want to have a class of electric light:
This will not affect the behavior of any other devices when switched; it will also not change the way in which switching lights on and off is reported. The player will still see "You switch the sodium lamp on." or the like. In this case that is probably what we want. If we wanted a special way of describing turning on electric lights as opposed to all other devices, we could also add an after rule for the electric light class. Adding this rule to the carry out train does guarantee, though, that in no case will we manage to make the lamp lit without actually making it switched on (or vice versa).
The sodium lamp is an electric light in the Stooped Corridor. "[if switched on]The sodium lamp squats on the ground, burning away.[otherwise]The sodium lamp squats heavily on the ground.[end if]". The description is "It is a heavy-duty archaeologist's lamp, [if switched off]currently off.[otherwise]blazing with brilliant yellow light.[end if]"
So far so easy. Since we've built the description of its light or darkness into the lamp's description, though, we may want to get rid of the "...is switched on" line that automatically follows when we look at something. For this we do need to borrow from a later chapter:
Suppose we intend a game in which the player needs to cut things open on a regular basis. We'll want to check whether he has the proper tools handy, and deal graciously with commands such as CUT [something] when no tool is specified. So:
We'll need a way to account for all these cuts and rips.
Definition: a thing is ripped if the count of rips of it > 0. A thing has a number called the count of rips. After examining something ripped, say "You see [the count of rips of the noun in words] rip[s] in [the noun][if something is in the noun], revealing [a list of things in the noun][end if]."
Moreover, because open containers normally list their contents when examined but we'd prefer Paddington's to be mentioned in the ripping paragraph:
So far, so good. But suppose that we'd like cutting also to make containers be permanently open and impossible to close again. We could write an "instead" rule, but that would mean that only our instead instructions would take effect, overriding the normal cutting it with rules entirely. Better would be to add a second carry out rule:
Now our rule will occur whenever a container is cut, but play will still go on to the reporting stage. And indeed we can add more of these, of varying degrees of specificity:
For that matter, we might want to add a report rule as well, to occur after the "You slash..." rule, so that every time the player cuts something open which has contents, the contents will be listed.
This time we do not add the condition to the rule (i.e., Report cutting an open noun...) If we did, this report rule would be more specific than the general report rule, and would occur first.
The teddy bear is a closed thing in the Safehouse. The description is "Fluffy[if the head is part of the bear], with an outsized head[otherwise], but headless[end if]." The head is a closed part of the teddy bear. In the bear is a large wad of stuffing. In the head are a small wad of stuffing and a packet of smuggled diamonds.
Here is a final nicety to get rid of the "which is closed" statement on our closed unopenable teddy bear, using an "activity" rule:
Delicious, Delicious Rocks
In some cases, we may want to add new stages to action processing. One possibility is a stage where we check the sanity of what the player is trying to do before executing any of the other commands; so that we avoid, for instance
Here is how we might insert such a stage in our action processing, using rulebook manipulation.
Notice that now Inform does not try taking the rock before rejecting the player's attempt to eat it.
It is of course possible to get the same effect with
...and in a small game with few rules, there's not much reason to add an extra stage. The ability to modify the stages of action processing becomes useful when we have a fairly large game with sophisticated modeling and want to be sure that some kinds of message (such as the sanity-check) are always handled before other things that we might be doing at the before stage (such as generating implicit actions like opening doors before going through them).
Suppose the current sequence of action handling is not quite enough for us: we'd also like to have a stage after reporting, where other characters can react to the player character's behavior after it has already happened and been reported on screen. Having such a stage is unlike using "after", because after occurs before reports and prevents them from being printed. So, for instance, we could allow the player to do any of a range of different actions that make loud noises, and have a nervous bird that reacts to all of them by flying away afterward.
To do this, we can add a new rule into the specific action-processing rules. (For a list of these, see the Rules index.) Moving rules around and adding new ones requires syntax that we will learn in the chapter on Rulebooks, but the present example is fairly straightforward: