[pro] Sub-function free variable binding differences between Scheme and CL

[Burton Samograd]

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 at gmail.com> wrote:
> Burton Samograd <burton.samograd at 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.