Hello,

I solved this with a backquote (instead of quote), I write this just in
case someone need an example (of what NOT to do :-D ).

Giovanni Biscuolo <giovanni@biscuolo.net> writes:

[...]

> If I use this:
>
> --8<---------------cut here---------------start------------->8---
>
> :html-preamble-format (("en"
> 			(xmlgen
> 			 '(div
> 			   (div
> 			    (a :href "/" "Home")
> 			    (span :class "pre-sep" "|")
> 			    (a :href "/colophon.html" "Colophon")))))
> 		       ("it"
> 			(xmlgen
> 			 '(div
> 			   (div
> 			    (a :href "/" "Home")
> 			    (span :class "pre-sep" "|")
> 			    (a :href "/colophon.html" "Colophon"))))))
>
> --8<---------------cut here---------------end--------------->8---

OK the code above was included as part of <<sites_config>> in a list
like this:

--8<---------------cut here---------------start------------->8---

      (setq org-publish-project-alist
	  '(
	    <<sites_config>>))

--8<---------------cut here---------------end--------------->8---

In this way all the sites_config part is _quoted_ (see the quote ad the
beginning of the org-publish-project-alist).

If I want the xmlgen code above to be evaluated, I have to backquote the
list and use the evaluator symbol (",") for the (xmlgen ...) block; this
way:

--8<---------------cut here---------------start------------->8---

      (setq org-publish-project-alist
	  `(
	    [OMISSIS]
            :html-preamble-format (("en"
            			,(xmlgen
            			 '(div
            			   (div
            			    (a :href "/" "Home")
            			    (span :class "pre-sep" "|")
            			    (a :href "/colophon.html" "Colophon")))))
            		       ("it"
            			,(xmlgen
            			 '(div
            			   (div
            			    (a :href "/" "Home")
            			    (span :class "pre-sep" "|")
            			    (a :href "/colophon.html" "Colophon"))))))))
           
--8<---------------cut here---------------end--------------->8---

...OK, lesson learned! :-D


Happy hacking!
Giovanni.

-- 
Giovanni Biscuolo