| 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.

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.

The built-in behavior of Inform is to print a line after a device is examined, saying whether the item is on or off. This is often inappropriate, and we could simply turn off that behavior in general by instructing Inform to ignore the "examine described devices rule" (see the chapter on rulebooks). Perhaps, though, we would like continue to have a short passage about the action of any switched on device; we'd just like a little more control over what it says from time to time. And in that case, we might change the rule to give a new activity control over that portion of the description: "Aftershock" The time of day is 3:47 AM. When play begins, change the right hand status line to "[time of day]" The Downstairs Hallway is a dark room. "The only room in the house with no furniture and almost nothing on the walls. At times like this you always notice the crack in the plaster, originating near the light fixture and running almost all the way to the wall." A plastic jug of filtered water is in the Downstairs Hallway. The description is "Five gallons, not that that will last you very long, hot as it has been lately." The crack is scenery in the Hallway. The description is "No, the ceiling isn't going to fall on you today." An electric lamp is a kind of device. The light fixture is an electric lamp in the Hallway. It is switched on, lit, and scenery. The description is "A plain globe of frosted glass containing the light bulb. Nothing special, and you never think about it except when, as now, you are forced to spend hours in this room." The flashlight is an electric lamp carried by the player. The description is "A shiny red flashlight." The portable radio is a device carried by the player. The description is "A small battery-operated radio which you received for free with your subscription to US News & World Report. It has served you well through many earthquakes past." Now we need our activity: Showing action of something is an activity. Rule for showing action of something (called item): if the item is switched on, say "[The item] is switched on."; otherwise say "[The item] is switched off." Borrowing from the rulebooks chapter, we can replace the standard "examine described devices" rule with something that uses this activity. The new described devices rule is listed instead of the examine described devices rule in the carry out examining rules. This is the new described devices rule: if the noun is a device, carry out the showing action activity with the noun. Thus far we have essentially replicated the original behavior. But now we can write increasingly specialized rules to modify what happens: Rule for showing action of an electric lamp (called item): if the item is switched on, say "[The item] is lit[if the number of visible lit things is greater than 1], competing with [the list of visible lit things which are not the item][end if]."; otherwise say "[The item] is dark." Carry out switching on an electric lamp: now the noun is lit. Carry out switching off an electric lamp: now the noun is unlit. Rule for showing action of the flashlight: if the flashlight is switched on, say "A strong, narrow beam of light shines from the flashlight."; otherwise say "It is currently switched off." Rule for showing action of the radio: if the radio is switched on, say "Through the static, you pick up pieces of discussion: a 6.7 on the Richter scale, epicenter... something about Topanga... but it crackles out again."; otherwise say "The radio is silent. You're saving the batteries." And there might be other places where we also want to show what a device does when turned on: Instead of listening in the presence of the switched on radio: carry out the showing action activity with the radio instead. Report switching on something: say "You flip a switch. "; carry out the showing action activity with the noun instead. Test me with "examine light / switch light off / switch flashlight on / switch radio on / examine radio / examine flashlight".

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

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