em.html">BOOST_PP_TUPLE_ELEM</a>(3, 1, data) \
      ) \
   ) \
   /**/

// raise 'x' to the 'n'-th power
#define EXP(x, n) <a href="tuple_elem.html">BOOST_PP_TUPLE_ELEM</a>(3, 2, <a href="while.html">BOOST_PP_WHILE</a>(PRED, OP, (n, x, 1)))

EXP(4, 2) // expands to 16
EXP(2, 3) // expands to 8
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