Someone suggested I look into co-routines and decision trees when I had posted for some feedback on doing AI. The behavioral system is rather simple. New behaviors can be added very easily. It all goes back to TRUE and FALSE.

Using this basic layout, what would be some key features you think to making a behavior system seem almost realistic (using this same format below):

--DECISION TREE EXPLORATION
 
--States
normal = true
happy = false
sad = false
worried = false
afraid = false
 
--Conditions
got_some_money = false
bump_your_head = false
loose_wallet = false
walk_into_dark_room = false
 
--Control
function GetEmotional(emotion)
emotion = true
end
 
 
--What if we want an animation to play if they are happy:
 
--TRIGGERS
if got_some_money then
GetEmotional(happy)
end
 
 
--REACTIONS
function JumpForJoy()
if happy then
playAnimation(object,animationID)
end
end
 
function Frown()
if sad then
playAnimation(object,animationID)
end
end
 
function BeAfraid()
if walk_into_dark_room then
playAnimation(object,animationID)
end
end
 
 
--Multiple conditions?
if bump_your_head and walk_into_dark_room then
GetEmotional(sad)
GetEmotional(afraid)
end

making a behavior system seem almost realistic

I really would like to help, but phrases as the quoted one make it really hard. Almost realistic behavior is really fuzzy. If I would take it literal, I would say, that it is just impossible. Behavior in games is really hard and really far away from being realistic, so my best sugguestion would be to start with behavior trees.

Chris Hecker gives some good insight in behavior trees over here. Start to understand how a behavior tree works (do a simple lua imlpementation) and try to write a simple bot to get the abilities of this approach.

It all goes back to TRUE and FALSE.

Realistic states aren't on or off. They have analogue levels. Perhaps a direction to go would be to make something like happiness a float value between 0 (suicidal) and 1 (deliriously joyful), along with a range of other attributes then have the conditions add or subtract values from these states, the have the behaviours based on whether states are above or below certain values.

Then if your character has_money and bumps_head he'll be feeling on balance that things are about average overall.

Wow. This was really easy to implement quickly into my Senses System.

mood = 5
 
function ChangeEmotion()
 
if mood >=0 and mood < 4 then
sad = true
normal = false
happy = false
setText(txt_readout,"I am sad")
end
 
if mood>=4 and mood <=6 then
sad = false
normal = true
happy = false
setText(txt_readout,"I am normal")
end
 
if mood >6 and mood <=10 then
sad = false
normal = false
happy = true
setText(txt_readout,"I am happy")
end
end

function TriggerEmotionChange()
if isCollisionBetween(eyes,box) then
mood = 10
elseif isCollisionBetween(eyes,monkey) then
mood = 3
elseif isCollisionBetween(eyes,building) then
mood = 5
end
end

-- Scene Update
function onSceneUpdate()
ChangeEmotion()
TriggerEmotionChange()

The mood is initialized at 5 (normal). The ChangeEmotion() function just checks what value the mood is at and does something. Simply by changing the mood value, I can trigger other things. I could even gradually increase or decrease the mood based on a certain environment. Link that to a graphic and you have the base of the Sims AI system almost. haha.

For me, environment change would just be a collision test.

I could associate each mood value with a variable.

for instance:

happy = 6
happier = 8
happiest = 10

Then I could just do:

if mood = happiest then
--Do something
end