[Ecls-list] Trigger action when data structure is updated?

[Rui Maciel]

Juan Jose Garcia-Ripoll wrote:
> Just to give you an idea, when you define a structure or a class, the
> Common Lisp environment creates a number of functions or methods to
> access the individual slots. In the case of structures this is rather
> strict in the way it is done.
> 
> For CLOS objects one can change the class of the class that you are
> defining and thus customize the methods that are generated to access
> the class methods.
> 
> I am doing some emphasis on this because CELLS may or may not be
> ported to ECL, but what you want to do can be implemented very easily,
> if not in a very efficient way -- to change the slot accessors while
> preserving some of the optimizations you may then need to do some more
> work.

Sounds good. I believe that, in my case, efficiency wouldn't be extremely 
important as long as it would be possible to re-render the model without any 
relevant latency. So that may not be a problem at all.


> #+ecl
> (setf clos:*optimize-slot-access* nil)
> 
> (defclass my-metaclass (standard-class)
>   ())
> 
> (defmethod (setf clos:slot-value-using-class)
>   (value (class my-metaclass) object slot)
>   (format t "~&;;; Changing object ~A" object)
>   (force-output)
>   (call-next-method))
> 
> (defclass foo ()
>   ((a :initarg :a :accessor foo-a)
>    b)
>   (:metaclass my-metaclass))
> 
> (defparameter a (make-instance 'foo :a 4))
> 
> (print (foo-a *a*))
> 
> (setf (foo-a *a*) 3)
> 
> (print (foo-a *a*))

I tried to run your example on ecl and it appears it choked. The output is as 
follows:

<ecl-output>
<snip/>

> (defparameter a (make-instance 'foo :a 4))

;;; Changing object #<a FOO>
A
> (print (foo-a *a*))

The variable *A* is unbound.

Available restarts:

1. (RESTART-TOPLEVEL) Go back to Top-Level REPL.

Broken at SI:BYTECODES. [Evaluation of: (PRINT (FOO-A *A*))]

</ecl-output>


One other thing, when I try to run (RESTART-TOPLEVEL) this problem pops up:

<ecl-output>
>>  (RESTART-TOPLEVEL)

Debugger received error: The function RESTART-TOPLEVEL is undefined.
Error flushed.

</ecl-output>


I've installed ecl from source, as the version available through the Ubuntu 
repositories appeared to be a bit outdated (Version: 0.9j-20080306-5ubuntu1). 
Could this set of problems be caused by a botched installation?


Rui Maciel