MACRO(R,STATE) and iterates
PRED(R,STATE) is true.
In other words, expands to the sequence:
MACRO(R,STATE) MACRO(R,OP(R,STATE)) MACRO(R,OP(R,OP(R,STATE))) ... MACRO(R,OP(R,OP(...OP(R,STATE)...)))
The length of the sequence is determined by
#define PRED(R,STATE) BOOST_PP_LESS(BOOST_PP_TUPLE_ELEM(2,0,STATE),BOOST_PP_TUPLE_ELEM(2,1,STATE)) #define OP(R,STATE) (BOOST_PP_INC(BOOST_PP_TUPLE_ELEM(2,0,STATE)),BOOST_PP_TUPLE_ELEM(2,1,STATE)) #define MACRO(R,STATE) BOOST_PP_TUPLE_ELEM(2,0,STATE) BOOST_PP_FOR((0,3),PRED,OP,MACRO)
0 1 2
BOOST_PP_FOR() is a generalization of BOOST_PP_REPEAT(). This means that BOOST_PP_REPEAT() can be implemented using BOOST_PP_FOR(). However, BOOST_PP_REPEAT() was introduced earlier, is generally easier to use, and is still quite useful on its own.
BOOST_PP_FOR() can be used for multidimensional repetition simply by invoking BOOST_PP_FOR##R() directly.
BOOST_PP_FOR() currently does not implement automatic recursion. The reason for this is that it would lead to very poor performance. The automatic recursion technique takes O(N) steps just to find out that the Nth recursion should be used. This would dramatically effect the time complexity of macros using automatic recursion.
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