Re: [Boost-users] PP: how to use automatic recursion

Subject: Re: [Boost-users] PP: how to use automatic recursion
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-02-01 10:51:24

AMDG

Hicham Mouline wrote:
> I am trying to generate many types from 1 struct (for full background, please see thread "generate structs with all combinations of members from a given struct"), with the help of Boost.PP
>
> #include <boost/preprocessor/control/if.hpp>
> #include <boost/preprocessor/seq/size.hpp>
> #include <boost/preprocessor/seq/seq.hpp>
> #include <boost/preprocessor/seq/elem.hpp>
> #include <boost/preprocessor/arithmetic/sub.hpp>
> #include <boost/preprocessor/seq/pop_front.hpp>
> #include <boost/preprocessor/seq/push_back.hpp>
>
> #define STRUCTMEMBERS ((double,m1))((double,m2))((double,m3))((double,m4))((double,m5))
>
> #define SEQ_LAST_ELEM(seq) \
>   BOOST_PP_SEQ_ELEM( BOOST_PP_SUB(BOOST_PP_SEQ_SIZE(seq), 1), seq)
>
> #define UPDATE_MAIN_SEQ(mainseq, globalseq)\
>   BOOST_PP_IF( BOOST_PP_SEQ_SIZE(mainseq),\
>                BOOST_PP_SEQ_PUSH_BACK(\
>                 mainseq,\
>                 ((SEQ_LAST_ELEM(mainseq))(BOOST_PP_SEQ_HEAD(globalseq)))\
>         ),\
>                ((BOOST_PP_SEQ_HEAD(globalseq)))\
>       )
>
> #define COMBINATIONS(seq, combseq)\
>   BOOST_PP_IF( BOOST_PP_SEQ_SIZE(seq),\
>                COMBINATIONS( UPDATE_MAIN_SEQ(combseq,seq), BOOST_PP_SEQ_POP_FRONT(seq) ), \
>                combseq\
>              )
>
> #define COMBOS COMBINATIONS(STRUCTMEMBERS, BOOST_PP_SEQ_NIL)
>
> COMBOS
>
> Reading PP docs, I just realized that the preprocessor disallows recursion ( the COMBINATIONS macro calls itself in my case), but I didn't understand the reentrancy topic page.
>
> How can I change the above code to make the recursive COMBINATIONS possible?
>   

Look at http://sourceforge.net/projects/chaos-pp/.
I believe that it has a mechanism to support recursion.

In Christ,
Steven Watanabe