Re: execute defun on reception of signal

["Pascal J. Bourguignon" <pjb@informatimago.com>]

Emanuel Berg <embe8573@student.uu.se> writes:

> Rusi <rustompmody@gmail.com> writes:
>
>> However on a docs-improving note here's this little
>> titbit: [On other thread] There was this claim
>> "letrec is nice" or some such. Since I know letrec
>> from scheme etc but never seen in elisp I was
>> curious. I find: describe-function tells nothing
>> about the recursion the elisp info pages (index)
>> seems to not have it at all
>
> There is no mention of "letrec" in
>
>     /usr/share/info/emacs-24/elisp.info
>
> I don't know the policy. Are *all* functions, macros,
> etc. supposed to be in the Elisp manual?

letrec is not emacs lisp, it's scheme.

In Common Lisp, one would use labels, so in emacs lisp you can write:

    (require 'cl)
    (defun fact (n)
      (labels ((f (n f)
                 (if (plusp n)
                     (f (- n 1) (* n f))
                     f)))
        (f n 1)))

provides a nice tail-recursive factorial implementation.

    (fact 10) --> 3628800
    (fact 41) --> 1716706262231547904


-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk