I apologize, my original code was using labels but I copied the one using flet for this question. Please assume that I am using labels; the variable binding question still stands. I am asking this on the Pro list because it seems that everyone is on the same lists anyways and I get the best answers from the list. I can send it somewhere else if you have a suggestion where I would get the same quality of answer as here. -- Burton Samograd On Mon, Mar 5, 2012 at 6:23 AM, Stas Boukarev <stassats@gmail.com> wrote:
Burton Samograd <burton.samograd@gmail.com> writes:
Hello,
I am curently translating the logic circuit simulator code from SICP into Common Lisp and have run into a snag that I would like to ask about.
The Scheme code is as follows from section 3.3.4 (page 223 of my hardcover edition):
(define (and-gate a1 a2 output) (define (and-action-procedure) (let ((new-value (locical-and (get-signal a1) (get-signal a2)))) (after-delay and-gat-delay (lambda () (set-signal! output new-value))))) (add-action! a1 and-action-procedure) (add-action! a2 and-action-procedure))
The code basically binds the local function and-action-procedure into a list of functions in a1 and a2 which are then called by another routine later to perform the action when a value is set on the wire.
My translated Common Lisp code is:
(defun make-and-gate (a1 a2 output) (flet ((logical-and (a b) (if (= a 1) b a)) (and-action-proc () (let ((new-value (logical-and (get-signal a1) (get-signal a2)))) (set-signal output new-value)))) (add-action a1 #'and-action-proc) (add-action a2 #'and-action-proc))) You should use LABELS instead of FLET, FLET doesn't make its definitions available inside definitions so the call logical-and in and-action-proc can't find logical-and.
And seriously, writing to the _pro_ mailing list to ask trivial questions?
-- With best regards, Stas.