How to define callback functions

Hi all,
(i'm new to UFFI so if this is a FAQ please apologize- I didn't find
this information in the list archive or in the documentation)

I want to make an interface to a library (expat) that wants function
pointers as parameter (that are later called on specific events by the library), i.e.:

typedef void (XMLCALL *XML_EndElementHandler)(void *userData, const XML_Char *name);

void XMLCALL XML_SetEndElementHandler(XML_Parser p, XML_EndElementHandler);

Obviously i want the XML_EndElementHandler() to be a LISP function.

How can i do this ?

Thanks in advance

Regards
AHz