The BOOST_PP_LIST_FILTER macro filters a list according to a supplied criterion.
	
	Usage
		
			BOOST_PP_LIST_FILTER(pred, data, list)
		
	Arguments
		
			- 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.
		
		
			Previously, this macro could not be used inside BOOST_PP_WHILE. 
			There is no longer any such restriction. 
			It is more efficient, however, to use BOOST_PP_LIST_FILTER_D in such a situation.
		
	See Also
		
	Requirements
		
	Sample Code
#include <boost/preprocessor/comparison/less_equal.hpp>
#include <boost/preprocessor/list/filter.hpp>
#define LIST (1, (3, (2, (5, BOOST_PP_NIL))))
#define PRED(d, data, elem) BOOST_PP_LESS_EQUAL(elem, data)
BOOST_PP_LIST_FILTER(PRED, 3, LIST)
   // expands to (1, (3, (2, BOOST_PP_NIL)))