Re: Advice on ST-Object data-structure setup

[ken.dickey@whidbey.com]

On 2024-04-20 02:49, Mikael Djurfeldt wrote:

> Have you looked at Guile's OOP system GOOPS?

Thanks, Mikael.

I have implemented a number of object systems, including CLOS style 
systems such as GOOPS.

The mismatch here is in the overhead of the multimethod dispatch.

I would like something fairly efficient -- and without using caches if 
possible.

You probably know/have seen this, but back to basics...

If you look at the `behavior` function in 
https://github.com/KenDickey/Crosstalk/blob/master/guile-st-kernel.scm 
you will see that the basic dispatch mechanism is (primLookup: (behavior 
self) selectorSym) where the lookup is just a hash-table lookup with 
suitable failure handling.

(define (primLookup: methodDict symbol)
   (hashtable-ref methodDict
                  symbol
                  (lambda (self . rest-args)
                    (send-failed self symbol rest-args)))
                    ;; (make-messageSend self symbol rest-args)))
)

The natural way to interoperate with Scheme data types is to use type 
tag as an array index into a vector of functions which return a suitable 
behavior/hash-table.

For generic Smalltalk objects, this is just the first slot of a vector 
of value slots.  For typical Scheme objects, this is a method-dictionary 
for that kind of object.  So Scheme vectors, numbers, #true, closures, 
and so forth just work as expected when viewed as Smalltalk Arrays, 
numbers, true, BlockClosures..

So after optimization, dispatch mechanics is just mask the tag, shift, 
index, hash, apply.

The hard parts have to do with thisContext (call/cc interactions) 
keeping a proper debugging context, and Smalltalk`become`.

It appears that Guile has evolved to have suitable low-level mechanisms 
to be able to do this.

I find things out by writing code.  "If it works, it must be possible."

So my investigation is to get a basic Smalltalk working and then get 
into the compilation and runtime mechanics to see if I can make this 
efficient enough.

Starting with a CLOS style dispatch is a bit further from where I want 
to end up.

Thanks again for the thoughtful comments,
-KenD