Index: Radios and other devices active when switched on
Description: 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 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:
carry out the showing action activity with the noun;
now examine text printed is true.
Thus far we have essentially replicated the original behavior, but we've made it possible to write specialized behavior for devices, and to invoke that behavior in other places:
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].";
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 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."
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."
Instead of listening in the presence of the switched on radio:
carry out the showing action activity with the radio instead.