| Chapter 12: Advanced Actions |

| 12.16. 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 fail), 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.";
> allow access.

> A rule for reaching inside open containers:
> if the person reaching is the player begin;
> say "Your hands seem enigmatically too large for [the container in question].";
> deny access.
> end if.

The "person reaching" is, as its name suggests, the person trying to reach through the barrier in question.

176
| Example Magneto's Revenge Kitty Pryde of the X-Men is able to reach through solid objects, so we might implement her with special powers that the player does not have...

177
| Example Dinner is Served A window between two locations. When the window is open, the player can reach through into the other location; when it isn't, access is barred.

"Dinner is Served" Street in Kolonaki is a room. "There is a single round table out on the street here, and a window more or less at knee level looks down into the Olive Tree Gyro Shop, which is partly basement." 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: A procedural rule: if the window is open, ignore the can't reach inside rooms rule; otherwise substitute the can't reach through closed window rule for the can't reach inside rooms rule. This is the can't reach through closed window rule: if the home of the item described is not the location begin; say "You can't reach through the closed window."; rule fails; end if. To decide what room is the home of (item - a thing): let uppermost be the holder of the item; while uppermost is not a room, let uppermost be the holder of uppermost; decide on uppermost. And the rest is window-dressing. After looking when a room (called the next room) is adjacent: try examining the next room. Instead of examining a supporter, say "On [the noun] [is-are a list of things on the noun]." Instead of examining a container, say "In [the noun] [is-are a list of things in the noun]." 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, transparent, 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. Understand "examine [any adjacent room]" as examining. Instead of examining a room: say "Over in [the noun], you can see [a list of visible things in the noun]." After deciding the scope of the player: if the player is in the Street, place the Shop in scope; if the player is in the Shop, place the Street in scope. Test me with "examine shop / open refrigerator / open window / examine shop / open refrigerator / get beer / in / examine street".

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