Re: structured programming of automata with behavior trees

Sounds cool.

Is there a way to check it out with Squeak JS?

I had a colleague (a long time game developer) who implemented the behavior
tree on top of Croquet JS. It worked well for the purpose. I kind of liked
a more general and meta solution, and later created a Functional Reactive
Programming based system called Renkon. Croquet and Renkon use explicit
logical time. Your Behavior Tree implementation probably shares the
property of "at a logical time t, a node has at most one value", or "a node
is evaluated at most once at an evaluation cycle". I am getting to like
this property more and more nowadays.

On Sun, Jul 12, 2026 at 8:38 AM Lauren Pullen <[email protected]> wrote:

> Greetings List,
>
> I thought I'd follow the spirit of the upcoming Squeak release to work
> on improving some of my programs.  If you had previously looked at
> Cephei-BehaviorKernel and thought it looked like a neat, but
> impractical, toy, and weren't quite sure why, the answer was you
> couldn't create subroutines.
>
> And now, as of lrnp.12, you can!  Wander over to BTSubtree's example1
> for a nostalgic demo.
>
> For those of you just tuning in, a behavior tree uses an execution model
> completely unlike smalltalk's.  Smalltalk uses the normal successor,
> PC=PC+1, while a behavior tree uses a boolean successor, like Prolog.
> Control flow is based on the shape of the tree and whether you used an
> AND, OR, or NOT node to combine nodes.  Unlike smalltalk and prolog,
> behavior trees use 3-valued logic (success, failure, and incomplete).
>
> If you disregard the "incomplete" value, you can represent boolean
> successor in regular smalltalk code.  It looks like this:
>
> ^self m1 and: [self m2 and: [self m3 or: [self m4]]].
>
> Instead of writing statically-compiled methods, Cephei-BehaviorTree
> defines procedures dynamically using 1st-class objects and simulates a
> boolean successor machine.
>
> My behavior tree implementation is designed to augment my dynamic Mealy
> finite-state automata implementation (in StarVariable).  Instead of
> implementing Harel statecharts or relying on backtracking to enforce
> interlocks you use behavior trees to guard against sending improper
> input to the FSM, and more.
>
> This is a pretty low-level tool, but it's object-oriented.  Any instance
> can be a node if you define the methods from BTNode's instance side.
> The bare minimum is #tick:; the dynamic environment (a StarDictionary)
> is passed as the argument, and it must answer one of true, false, or nil.
>
> (A BTShallowBinder only extends the dynamic environment.  It's a
> subnode's responsibility to put something useful in the slot.  Low level
> gives you flexibility.)
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-- 
-- Yoshiki

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