Re: structured programming of automata with behavior trees

I have this app:

https://github.com/yoshikiohshima/renkon-pad

Where you can make a collaborative Croquet app collaboratively.

Its documentation is not quite there yet but I think we'll have something
readable soon.

On Fri, Jul 17, 2026 at 5:34 PM gettimothy via Squeak-dev <
[email protected]> wrote:

>  You typed "Croquet" and that caught my eye. I will have to research this.
>
> At first glance "Behavior Tree" sounds like a "State" design pattern.
>
>
> all the best.
>
>
> t
>
>
>
> From: Yoshiki Ohshima via Squeak-dev <
> [email protected]>
> To: "The general-purpose Squeak developers list"<
> [email protected]>
> Cc: "Yoshiki Ohshima"<[email protected]>
> Date: Mon, 13 Jul 2026 12:37:26 -0400
> Subject: [squeak-dev] 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:
>
>
>
> --
> -- Yoshiki
>
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>
> 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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