Re: New, from-scratch implementation of backquote.

On 11 Apr 2003, Todd Sabin wrote:

> Perhaps it's obvious, but the last message was unfinished; I never
> noticed how close C-c C-c is to C-x C-x before :\
> 
> Anyway, the code I sent doesn't do what I thought it did, so just ignore
> me for now... :)

Yep. It returns the list (defclass ...) which still needs to be EVAL-ed. 

You can't fix this, because you can't get around the fact that defclass
is a compile-time construct.

To define a new class at run-time, you need to construct a new instance
of the defclass syntax, and to activate it, you must either EVAL it,
or put it in a lambda body and COMPILE it, and then funcall the
resulting object.

The other alternative would be to use the underlying ENSURE-CLASS
function, but that is not portable, (except where the MOP is
implemented)?

So we can repair your function by moving the backquote out to the whole
lambda, and then by using the COMPILE function---which is probably kind
of a waste of cycles just to run defclass once. ;)

;; original recipe
(defun defclass* (name supers slots &rest options)
  (funcall (lambda () 
             `(defclass ,name ,supers ,slots ,@options))))

;; extra crispy
(defun defclass* (name supers slots &rest options)
  (funcall (compile nil 
                    `(lambda () 
                       (defclass ,name ,supers ,slots ,@options)))))

;; calorie reduced
(defun defclass* (name supers slots &rest options)
  (eval `(defclass ,name ,supers ,slots ,@options)))



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