The BOOST_PP_LIST_FILTER_D macro filters a list according to a supplied criterion. 
		It reenters BOOST_PP_WHILE with maximum efficiency.
	
	Usage
		
			BOOST_PP_LIST_FILTER_D(d, pred, data, list)
		
	Arguments
		
			- d
- 
				The next available BOOST_PP_WHILE iteration.
			
- pred
- 
				A ternary predicate of the form pred(d, data, elem). 
				This predicate is expanded by BOOST_PP_LIST_FILTER for each element in list with the next available BOOST_PP_WHILE iteration,
				the auxiliary data, and the current element in list. 
				This macro must return a integral value in the range of 0 to BOOST_PP_LIMIT_MAG. 
				If this predicate expands to non-zero for a certain element, that element is included in the resulting list.
			
- data
- 
				Auxiliary data passed to pred.
			
- list
- 
				The list to be filtered.
			
Remarks
		
			This macro expands pred for each element in list. 
			It builds a new list out of each element for which pred returns non-zero.
		
	See Also
		
	Requirements
		
	Sample Code
#include <boost/preprocessor/comparison/less_equal.hpp>
#include <boost/preprocessor/list/filter.hpp>
#include <boost/preprocessor/list/fold_right.hpp>
#define A (1, (2, (3, (4, BOOST_PP_NIL))))
#define B (A, (A, (A, (A, BOOST_PP_NIL))))
#define PRED(d, data, x) BOOST_PP_LESS_EQUAL(x, data)
#define OP(d, state, x) (BOOST_PP_LIST_FILTER_D(d, PRED, 2, x), state)
BOOST_PP_LIST_FOLD_RIGHT(OP, BOOST_PP_NIL, B)
/*
   expands to:
   ((1, (2, BOOST_PP_NIL)), 
   ((1, (2, BOOST_PP_NIL)), 
   ((1, (2, BOOST_PP_NIL)), 
   ((1, (2, BOOST_PP_NIL)), 
      BOOST_PP_NIL))))
*/