| 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.

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