A rather abnormal use of a StopEventList.

Authoring TADS
1

This is a weird one…

I was wondering if it’s possible to make an EventList, a StopEventList specifically, go through certain events if a certain property is set to true, and another event if it’s set to nil. In short, if a == true, show these events and if a == nil, show these others.

To catch the obvious question of why not simply trigger another StopEventList, I’m brutalizing somebody else’s code and finding a way to redirect this to another EventList would be an enormous amount of extra work. That’s why I was wondering if it’s possible to insert the check within the stopEventList itself.

2

Yes, although the implementation depends on how you want to track your position in each list. Here’s one approach that treats the lists as independent - they can have a different number of events and can reach the stopped state at different times.

modify StopEventList
	altList = []

	getAltState() {
		return altScriptState;
	}

	advanceAltState() {
		if (altScriptState < altList.length())
			++altScriptState;
	}

	altScriptState = 1

	altDone() {
		advanceAltState();
	}

	doScript() {
		local idx, lst, done;
		if (check()) {
			idx = getScriptState();
			lst = eventList;
			done = &scriptDone;
		}
		else {
			idx = getAltState();
			lst = altList;
			done = &altDone;
		}

		if (idx >= 1 && idx <= lst.length()) {
			doScriptEvent(lst[idx]);
		}

		done();
	}
	
	check() {
		return true;
	}
;

And here is a simple test case.

testEvents: StopEventList
	eventList = ['Yes', 'Affirmative', 'Understood', 'OK']
	altList = ['No', 'Never', 'Negative', 'Stop']

	check() {
		_value ++;
		return (_value % 2 == 0 ? true : nil);
	}
	
	_value = 1

;

modify WaitAction
	execAction() {
		testEvents.doScript();
	}
;

The modified StopEventList class will work as usual unless you override the check() function. If check() returns nil then it will display an event from altList.

3

That did it. I wanted only a few specific EventLists to have this behaviour, so all I have to do is make check() look for the state of the relevant property and return true or nil depending on its state.

Thank you very much, you saved me a really big load of work.

4

Crap, I’m still not done.

There’s one, and I think final, hitch I need to sort. In the above problem, both the plain EventList and the AltList are StopEventLists. For the behaviour I’m thinking of, it would work better if the altList where a ShuffledEventList instead.

…thinking about it, the best idea I get is to stick an embedded expression in the altList to fire a separate ShuffledEventList which contains the events previously in the altList. So if A == true, the regular StopEventList will fire and if A == nil, the altList will redirect things into the ShuffledEventList.

I know I can stick an embedded expression in an EventList like

EventList [ {: “<<something()>>” } ]
But I don’t know how to trigger an EventList from scratch (I’ve always worked by piggybacking on pre-existing code like atmospereList and the stuff I’m clumsily defacing right now). Can I do that?

5

Yes. You probably also want to redefine advanceAltState() to roll back around, or to do nothing at all.

myCrazyList: StopEventList
   altList = [ {: someShuffledEventList.doScript() } ]

   advanceAltState() {}
;
6

Haha, I deserved the “crazy” thing.

That worked perfectly, thank you.