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Subject: accessing a cell of neighborhood containing another agent
From: Pierre-Marcel GORAL (corran_pmg@hotmail.com)
Date: Fri Mar 12 2004 - 17:00:20 CET
Hello everybody!
Proceeding with the secund tutorial of the CIRAD site, I've tried to ameliorate the model Forager-Plant by introducing Predators. I'm a very beginner in Cormas, so excuse me if the answer to my problem is trivial ;-) .
The problem is to make a predator go to a cell of its neighbourhood where there is a prey for him. I've tried to use several function, but it seems that ther aren't the good ones: a major bug is often : "smthing must be Boolean", or even "proceed for truth"! It seems, so, that I couldn't use properly "theOccupants at", for example. I tried also to go on with "perceivedEntities", but I got the same kind of error messages.
Here is my last version of the code:
MOVE
| preyNeighbours |
"BUG!!! trouver une fonction identifiant le fait qu'une cellule soit occupée par un agent de classe Forager"
preyNeighbours := self patch neighbourhood select: [:cell | cell theOccupants at: #Forager ].
preyNeighbours isEmpty
ifTrue: [self randomWalk]
ifFalse: [self leave. self moveTo: (Cormas selectRandomlyFrom: preyNeighbours)].
It'll be nice of you if you pay attention to this problem, because it's really annoying not finding solution to such a simple but important function.
Nothing less to the Zero fighter! 
Pierre-Marcel GORAL