Hi Peter,

Sorry for the really long delay, but I am only slowly regaining my normal life... ;-)

On 27 Nov 2004, at 13:52, ml13@onlinehome.de wrote:

Hi,

I am trying to extend the test example to use a special function that is recursive. As an example, I am defining f(x) to compute the sum of the squares

...

from 0 to x.

When I am trying to dynamically redefining the function to simply add 1 to its result, this new definition seems to get called "inside" as well.

Yes, that's right. The methods that you add with dynamic scope are active for the respective generic function no matter when and how you call it. So even in a recursive call they get called as well when they are applicable.

What do I have to do to get the (assert (eql (f 5) 56))) working??

Special functions use the special method combination by default that allows you to :override an existing method. This means that an overriden method is canceled out for the current dynamic scope - i.e., it is never executed in the current dynamic scoped. You can make use of this to do what you want. Here is the code:

(in-package :al-user)

(define-special-function f (x) (:definer f*))

(defmethod f* ((scope t) x) (if (zerop x) 0 (+ (* x x) (f (1- x)))))

(assert (eql (f 5) 55))

(with-special-function-scope (f*) (defmethod* f* :around ((scope dynamic) x) (1+ (with-special-function-scope (f*) (defmethod* f* :override :around ((scope dynamic) x) (call-next-method)) (call-next-method)))) (assert (eql (f 5) 56)))

(assert (eql (f 6) 91))

The trick is a) to use an :around method and b) to :override that :around method with a "skipping" method inside itself. a) is important because if you would otherwise use a primary method there would be no way to override just the newly added one.

(It might be a good idea to draw a diagram for the interaction in order to understand the control flow.)

I hope this helps. Maybe you're right that this should be simpler, so I will keep this in mind for possible future changes or additions.

PS: By the way, is there possibly any example existing of the cached fibonacci function using the current version of aspectL?

I don't have any at hand at the moment, sorry. Should be simple though, right? ;)

Cheers, Pascal

-- Tyler: "How's that working out for you?" Jack: "Great." Tyler: "Keep it up, then."