#include <boost/preprocessor/arithmetic/mul.hpp>
#include <boost/preprocessor/arithmetic/dec.hpp>
#include <boost/preprocessor/control/while.hpp>
#include <boost/preprocessor/tuple/elem.hpp>
#define PRED(d, data) BOOST_PP_TUPLE_ELEM(3, 0, data)
#define OP(d, data) /* ............... */ \
( \
BOOST_PP_DEC( \
BOOST_PP_TUPLE_ELEM(3, 0, data) \
), \
BOOST_PP_TUPLE_ELEM(3, 1, data), \
BOOST_PP_MUL_D( \
d, \
BOOST_PP_TUPLE_ELEM(3, 2, data), \
BOOST_PP_TUPLE_ELEM(3, 1, data) \
) \
) \
/**/
// raise 'x' to the 'n'-th power
#define EXP(x, n) BOOST_PP_TUPLE_ELEM(3, 2, BOOST_PP_WHILE(PRED, OP, (n, x, 1)))
EXP(4, 2) // expands to 16
EXP(2, 3) // expands to 8