Inform 7 Home Page / Documentation
§12.18. Changing reachability
The question of what the player can, and cannot, reach to touch is important in interactive fiction. It contains some of the subtlest ideas in the model world, though they often go unnoticed. For instance, if a key is on a shelf which is part of a closed box, can we reach for the key? This comes down to whether the shelf, described only as "part of" the box, is on the inside or the outside: and in fact, because it cannot know which is the case, Inform allows either. So in general it is best to regard "parts" as being exterior parts, but to avoid having parts on containers that might in the course of play be closed up with the player inside.
We can, if we wish, change the principles of what can be touched by writing new reaching inside or reaching outside rules. Returning to the example of the conical flask:
A rule for reaching inside the flask: say "Your hand passes through the glass as if it were not there, chilling you to the bone."; allow access.
(Or this could equally be called "a reaching inside rule for the flask".) More generally, we could give the usual flexible description of what the rule applies to:
A rule for reaching inside open containers: say "Your hands seem enigmatically too large for [the container in question]."; deny access.
The "container in question" is the one to which the rule is being applied. Note that a reaching inside rule can "deny access" (stopping with failure), or "allow access" (stopping with success), or neither, in which case the decision is left up to any subsequent rules in the rulebook to make. If none of them decide, access is allowed.
If it seems possible that these rules will be employed by people other than the player, then we need to write them a little more carefully, and in particular we need to ensure that they print nothing for other people. In the first case below, anybody can reach through the glass; in the second case, only the player cannot reach into open containers.
A rule for reaching inside the flask:
if the person reaching is the player, say "Your hand passes through the glass as if it were not there, chilling you to the bone.";
A rule for reaching inside open containers:
if the person reaching is the player:
say "Your hands seem enigmatically too large for [the container in question].";
The "person reaching" is, as its name suggests, the person trying to reach through the barrier in question.
|Start of Chapter 12: Advanced Actions|
|Back to §12.17. Visible vs touchable vs carried|
|Onward to §12.19. Changing visibility|
The School for Gifted Youngsters is a room. Kitty Pryde is a woman in the School for Gifted Youngsters. "Kitty Pryde waits for you to say why you summoned her out of class." The description is "You see nothing special about Kitty Pryde. But that is only because she has learned to conceal her mutant powers: in fact she has the alternative name Shadowcat, and the ability to phase through solid objects."
The glass box is a container in the School for Gifted Youngsters. It is closed, openable, and transparent. In the box is a quantity of poisonous gas. In the box is a thing called the message from Magneto.
Now the player can get Kitty to take the message without releasing the poisonous gas:
It's tempting to handle the player's inability to interact with something with a simple instead rule:
Unfortunately, the rule does not address the case where the object in question is the second noun; so for instance the following example reveals the difficulty:
...where the response here behaves as though the sun is in reach. If we had a fully implemented tying action, the player would (even more disastrously) be allowed to lasso celestial objects.
We could add a second instead rule as well:
Instead of doing something other than examining when the noun is a view:
say "You are too far from [the noun] to do anything but look."
Instead of doing something other than examining when the second noun is a view:
say "You are too far from [the second noun] to do anything but look."
This produces acceptable output again, but there is a more elegant way, one that works better with Inform's existing world model. Currently the default model assumes that accessibility -- whether the player can reach something or not -- is checked between the Before... rules and the Instead... rules. We can add our own accessibility rules, including this one to govern whether views are accessible. So for instance:
Accessibility rule (this is the can't touch views rule):
if the action requires a touchable noun and the noun is a view:
say "You are too far from [the noun] to do anything but look." instead;
if the action requires a touchable second noun and the second noun is a view:
say "You are too far from [the second noun] to do anything but look." instead;
Now our new accessibility rule fits into its proper stage.
Dinner is Served
The Street contains a round table. The table is scenery. On the round table is a plate. On the plate are a gyro and a mound of fresh potates. The plate is portable. The potates and the gyro are edible. The description of potates is "They'd be called french fries, at home, but these are steak-cut and fried in olive oil." The description of the gyro is "Dripping garlic-yogurt sauce."
Olive Tree Gyro Shop is inside from Street in Kolonaki. Kostis is a man in the Gyro Shop. In the Shop is a stand. On the stand is a rotating column of cooking lamb flesh. In the shop is a closed, openable container called a drinks refrigerator. The refrigerator contains a can of Mythos beer and a can of Coke Light.
Here's the part that allows reaching through the window.
We replace the usual rule that says the player can never reach into a room with one that more specifically checks whether we are trying to reach through the window. If we aren't, we return the usual refusal. If we are, we return a custom refusal if the window is closed ("You can't reach through the closed window"), but allow access if the window is open.
This is the can't reach through closed window rule:
let reaching through the window be false;
if the container in question is a room and the container in question is not the location:
if the container in question is the Street and the location is the Olive Tree Gyro Shop:
now reaching through the window is true;
if the container in question is the Gyro Shop and the location is the Street:
now reaching through the window is true;
if reaching through the window is true:
if the window is closed:
say "You can't reach through the closed window.";
say "You can't reach into [the container in question] from here.";
And the rest is window-dressing.
The window is a backdrop. It is in the Street and the Shop. The window can be openable. The window can be open. The window is openable and closed. Instead of searching the window in the Street: try examining the shop. Instead of searching the window in the Shop: try examining the street.