FFI: optional argument in foreign calls

Hi,

How do we handle access to variadic foreign (C) functions?

E.g., in PARI/GP:

--8<---------------cut here---------------start------------->8---
factor(x,{lim}): factorization of x. lim is optional and can be set
whenever x is of (possibly recursive) rational type. If lim is set
return partial factorization, using primes < lim.
--8<---------------cut here---------------end--------------->8---

Is there a better way than

--8<---------------cut here---------------start------------->8---
(pari-call-out factor1 "factor" (x))
(pari-call-out factor2 "factor" (x (lim long)))
(defun factor (x &optional (lim nil limp))
  (if limp
      (factor2 x lim)
      (factor1 x)))
--8<---------------cut here---------------end--------------->8---

(I can probably wrap this into the pari-call-out macro, but the point is
-- do we really need *two* def-call-out forms?)

Thanks!

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
http://steingoldpsychology.com http://www.childpsy.net http://iris.org.il
http://jij.org http://mideasttruth.com https://ffii.org http://think-israel.org
"A pint of sweat will save a gallon of blood."          --George S. Patton

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