# Events

The Events module implements Daemons and Fuses. A Fuse is something that causes a piece of code to execute after a set number of turns. A Daemon is something that causes a piece of code to be executed every turn or every so many turns. Daemons and Fuses in adv3Lite are very similar to those in adv3.

To create set up a fuse, just create a new Fuse object thus:

new Fuse(obj, prop, turns)

This defines a Fuse that will call obj.(prop), i.e. the prop method of obj, after turns turns. If turns is 0 then the Fuse will execute on the same turn.

For example, to define an alarm clock that rings in 10 turns' time after you push a button on it, we could define:

    alarmClock: Thing 'alarm clock'
    	"It has a big red button attached. "

    	ring()
    	{
    	   "The alarm clock starts ringing loudly. ";
    	   redButton.isDown = nil;
    	}
    ;

    + redButton: Component 'big red button'
        dobjFor(Push)
        {
            verify()
            {
                if(isDown)
                   illogicalNow('The button is already down. ');
            }

            action()
            {
                isDown = true;
                "You push the red button down. ";
                new Fuse(alarmClock, &ring, 10);
    		}
    	}

       isDown = nil
    ;

Note, by the way, that the property we want to execute has to be listed in the arguments to new Fuse as a property pointer, with an ampersand (&) immediately preceding its name.

A Daemon is defined in exactly the same way, except that instead of only executing once, it will execute every turns turns. If turns is given as zero, then the Daemon will execute on the current turn (i.e. after zero turns) and then every turn thereafter (until it is removed).

It's sometimes useful to store a reference to a Daemon so we can turn it off again:

daemonID = new Daemon(obj, prop, turns)

It may be, though, that the player character won't be around to see (or hear, or smell) the event that the Fuse or Daemon is reporting, in which case we'd ideally like to suppress any text that the Fuse or Daemon would otherwise display. We can do that using a SenseFuse or SenseDaemon. These can be created in exactly the same way as a normal Fuse or Daemon but any text they would otherwise display won't be displayed unless the player character can see the object passed as the obj parameter when the SenseFuse or SenseDaemon is created.

Occasionally this may not be what we want, since we want to test whether the object in question can be smelled or heard rather than seen. Or it may be that we want to test the visibility or audibility of some object other than the one we passed as the obj parameter, other, that is, than the object whose prop method the Fuse or Daemon is executing. In such a case we can define the Fuse or Daemon with one or two additional parameters:

new SenseFuse(obj, prop, turns[, senseProp, senseObj])

new SenseDaemon(obj, prop, turns[, senseProp, senseObj])

Where senseProp must be one of &canSee, &canHear or &canSmell (or conceivably &canReach) and senseObj is the object that must be sensed appropriately. Note that you can just supply the senseProp parameter if you want to test whether obj can be heard or smelled, but that if you supply the senseObj parameter you have to supply the senseProp parameter as well.

Finally, you can define a PromptDaemon which executes just before the command prompt on every turn:

new PromptDaemon(obj, prop)

There is also a OneTimePromptDaemon which, as its name suggests, is a PromptDaemon that executes only once (effectively a PromptFuse, though the adv3Lite library keeps the same name for this class as the adv3 library).

You may wish to stop a Daemon, or prevent a Fuse from executing before its due to fire. If you've stored a reference to the Fuse or Daemon you can disable it by calling its removeEvent() method, e.g.:

      daemonID.removeEvent();

If you haven't stored a reference to the Fuse or Daemon you want to remove, you can remove it by calling:

eventManager.removeMatchingEvents(obj, prop)

Where obj and prop are the object and property for which the Fuse or Daemon was originally created.

Finally, you can control the order in which Fuses and Daemons are processed by overriding their eventOrder property. The higher the eventOrder, the later the event; the default value of eventOrder is 100. This doesn't effect PromptDaemons which are always displayed just before the command prompt. Note that while other Fuses and Daemons may not be executed if the turn cycle is interrupted (by an abort statement, for example), PromptDaemons are always executed.

adv3Lite Library Manual
Table of Contents | Optional Modules > Events
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