recursive_function_pointer_shim.cpp

struct eat_char_fcn
{
	eat_char_fcn( struct eat_char_fcn (*inFun)( char currCh, xml_reader& reader, vector<shared_ptr<node>>& nod, attribute* att ) ) : function(inFun) {}
	
	struct eat_char_fcn operator()( char currCh, xml_reader& reader, vector<shared_ptr<node>>& nod, attribute* att ) { return function(currCh,reader,nod,att); }
	explicit operator bool() { return function != nullptr; }
	
	struct eat_char_fcn (*function)( char currCh, xml_reader& reader, vector<shared_ptr<node>>& nod, attribute* att );
};

Could even make this a macro like:

#define RECURSIVE_FUNC_PTR(name,params) struct name \
{ \
    name( struct name (*inFun)params ) : function(inFun) {} \
     \
    struct name operator()params { return function(currCh,reader,nod,att); } \
    explicit operator bool() { return function != nullptr; } \
     \
    struct name (*function)params; \
}

RECURSIVE_FUNC_PTR(eat_char_fcn,( char currCh, xml_reader& reader, vector<shared_ptr<node>>& nod, attribute* att ));

Note: Got a suggestion to make the operator bool explicit, which should prevent nasty accidental bool conversions.