🚀 go-pugleaf

In article <1992Nov23.192133.10895@jpl-devvax.jpl.nasa.gov>, charest@Aig.Jpl.Nasa.Gov (Len Charest) writes:
|> Generic classes would go a long way towards extending the expressiveness of
|> DEFMETHOD. However, they would not cover all of the discrimination strategies
|> I mentioned in my original post--especially the one I find most attractive: 
|> method selection based on the *value* of a variable. To wit:
|> 
|> (defun interesting-value-p (x)
|>   (eq x *interesting-value*))
|> 
|> (defmethod observe ((thing (satisfies interesting-value-p)))
|>   ...)

Am I missing something here, or is this exactly what "eql" method specializers
are for?  Namely:

	(defmethod observer ((thing (eql *interesting-value*)))
          ...)

In fact, these can be combined nicely with macros for slot-value methods:

	(defmacro observer (object)
          `(real-observer (a-slot object) object))

        (defmethod real-observer ((sval (eql *interesting*)) (object itsclass))
         ...)

Now, I can see that extending this to an arbitrary predicate would be useful
(as has already been suggested), but I also see how easily this would
explode into a performance nightmare.  

Joe Konstan
konstan@cs.umn.edu

[for examples of using slot-value methods, and related constructs, see
 "Developing a GUIDE using object-oriented programming" in OOPSLA '91]