How to use Nodes?

Monkey Forums/Monkey Beginners/How to use Nodes?

Midimaster

(Posted 2014) [#1]

I have a list with some objects in it. And I have already picked one element. But now I want to know the element which is the previous in this list. How can I do that?

something like that:

Class Domino
	Global All := New List<Domino>
	
	Field X%,Activ%
	
	Function CheckAll:Void(Pos%)
		For Local loc:Domino=Eachin All
			If Pos=loc.X
				loc.Activ=True
				loc.Previous().Activ=False ' how to do that????
			Endif
		Next
	End
End

It would be very helpful, if the manual has more informations and samples about the LIST class.

At the moment I know only this possibility:

All.Find(loc).PrevNode().Value().Activ=False

...but as I'm already "inside" the list, there must be a more elegant way, or?

Gerry Quinn

(Posted 2014) [#2]

You have to start with nodes in the first place, I think. I would write:

		Local nod:Node< Domino > = All.FirstNode()
		Repeat
			If Pos = nod.Value().x
				nod.Value().Activ = True
				nod.PrevNode().Value().Activ = False
			End
			nod = nod.NextNode()
		Until nod = Null

Note that either version will crash if the condition is met on the first node - you probably need a test there. (Or you could keep track of two nodes always, passing the current node to the previous one before calling NextNode().)

Now I come to think of it, you can indeed do it without nodes and using Eachin, by making a local prevLoc:Domino in which you store loc after each check:

Local prevLoc:Domino
For Local loc:Domino=Eachin All
	If Pos=loc.X
		loc.Activ=True
		prevLoc.Activ=False
	Endif
	prevLoc = loc
Next

Midimaster

(Posted 2014) [#3]

Thank you. Your second example is exactly what I did at least...

It looks like there is no chance to know which node is the "current" during a "For Eachin" loop.

Gerry Quinn

(Posted 2014) [#4]

Yes, I have found that sometimes you just have to accept that 'Eachin' is not enough. It happens with arrays too - you can use Eachin if you don't need to know which is current, but otherwise you must go back to For Local i:Int = 0 Until arr.Length()

computercoder

(Posted 2014) [#5]

Agreed. Something like how LINQ provides a nice way to grab at objects you are looking for without specifically looping through everything would be good. I've always had to search by looping as well in Monkey-X arrays and Lists.