| Chapter 17: Activities |

| 17.5. New activities

Activities are all about influencing the standard mechanisms which Inform uses, so it might at first seem that there is no need to create new activities: but on further reflection, quite a lot of the writing of interactive fiction involves creating new and systematic ways to do things, and as soon as we have a general rule, we will want to have exceptions. Inform therefore allows us to create our own activities, giving us ways to influence the operation of our own mechanisms.

There are two kinds of activity: those which relate to a specific thing or room, and those which do not. The following creates one of each kind:

> Analysing something is an activity.
> Assaying is an activity.

Here "analysing something" relates to a specific item: Inform knows this because it looks for the clue "something" (or "of something") after the activity's name, which in the first case above is simply "analysing".

Creating an activity is like creating an action: it automatically makes new rulebooks - "before analysing", "for analysing" and "after analysing" - but they start out empty, so the activity does nothing yet. Moreover, it never happens. We can make an activity happen at any time by writing phrases like so:

> carry out the analysing activity with the pitchblende;
> carry out the assaying activity;

To make the activity do something useful, we need to put a rule into its "for" rulebook:

> The last for assaying rule:
> say "Professionally, you cast an eye around mineral deposits nearby, noticing [list of rocks in the location]."

"The last" is a technicality about rulebooks (see the next chapter) which, put briefly, guarantees that this rule comes last among all possible "for assaying" rules. This is good form because the whole point of an activity is to make it easy for further rules to interfere - so we deliberately hang back to last place, giving precedence to anybody else who wants it.

It may look rather pretentious to dress up the footling little "assaying" example as an activity, but it gains us more than might first appear. Every new activity created provides a context which other activities can observe. We could, for instance, define

> Rule for printing the name of a rock while assaying: ...

so that during assays more technical names are used.

249
| Example AARP-Gnosis An Encyclopedia set which treats volumes in the same place as a single object, but can also be split up.

Suppose we have a complete Encyclopedia in our game. The player is allowed to pick up the whole set (there must not be too many volumes), but also to do things with individual volumes, and indeed to scatter these volumes all over the place. Putting a volume back in the same place as the rest of the Encyclopedia should, however, restore it to the collective. We will start out by defining general rules for collectives like this: "AARP-Gnosis" Fitting relates various things to one thing (called the home). The verb to fit (it fits, they fit, it is fitted) implies the fitting relation. Definition: a thing is missing if it is not part of the home of it. A collective is a kind of thing. Before doing something to something which is part of a collective: let space be the holder of the home of the noun; move the noun to the space. Instead of examining a collective: say "[The noun] consists of [the list of things which are part of the noun]." Now the real work begins. One reason to make this an activity is that we might easily want to override it for specific objects; for instance, the generic collecting activity here would not deal properly with collectives of clothing where some items might be worn and others not. In that case, we would want to write another, more specific "collecting" activity to handle the complexities of fashion. Collecting something is an activity. Every turn: repeat with item running through collectives begin; carry out the collecting activity with the item; end repeat. Before collecting a thing (called the item): let space be the holder of the item; if space is not a thing and space is not a room begin; if something (called the other space) contains at least two things which fit the item, move item to the other space; if a room (called the other space) contains at least two things which fit the item, move item to the other space; if someone (called the owner) carries at least two things which fit the item, move item to the owner; end if. Rule for collecting a thing (called the item): let space be the holder of the item; if space is a thing or space is a room begin; repeat with component running through things held by the space begin; if the component fits the item, now the component is part of the item; end repeat; if the number of things which are part of the item is 0, remove the item from play; if the number of things which are part of the item is 1 begin; let the last thing be a random thing which is part of the item; move the last thing to the space; remove the item from play; end if; end if. And now for a cheerful scenario: The Boise Memorial Library is a room. "A concrete box of a room, roughly eight feet by fourteen, which contains all the fallout shelter has to offer by way of entertainment. Someone with a grim sense of humor has tacked a READ! literacy poster to the door, as though there were anything else to do while you await the calming of the Geiger counters." The shelf is a supporter in the Library. "A battered utility shelf stands against the south wall." The New Idahoan Encyclopedia Set is a collective. Volume A-Aalto fits the Encyclopedia. It is part of the Set. Volume AAM-Aardvark fits the Encyclopedia. It is part of the Set. Volume Aarhus-Aaron fits the Encyclopedia. It is part of the Set. Volume AARP-Gnosis fits the Encyclopedia. It is part of the Set. Volume Gnu-Zygote fits the Encyclopedia. It is part of the Set. The Set is on the shelf. Let's have the Encyclopedia describe itself differently depending on whether it's all in one place: After printing the name of the Set when something missing fits the Set: say " (missing [a list of missing things which fit the Set])" Before printing the name of the Set when the number of missing things which fit the set is 0: say "complete "; Test me with "get aarhus-aaron / look / inventory / get aam-aardvark / look / get gnu-zygote / look / get aarp-gnosis / look / inventory / drop set / look / get set / get a-aalto / inventory".

250
| Example Aftershock Modifying the rules for examining a device so that all devices have some specific behavior when switched on, which is described at various times.

251
| Example Crusoe Adding a "printing the description of something" activity.

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