Description

The macro checks that the sequence is a Boost PP seq. If it is not a Boost PP seq, it forces a compiler error.

The macro normally checks for a Boost PP seq only in debug mode. However an end-user can force the macro to check or not check by defining the macro BOOST_VMD_ASSERT_DATA to 1 or 0 respectively.

d = The next available BOOST_PP_WHILE iteration.
sequence = a possible Boost PP seq.

returns  = Normally the macro returns nothing. 

           If the sequence is a Boost PP seq, nothing is 
           output.
          
           For VC++, because there is no sure way of forcing  
           a compiler error from within a macro without producing
           output, if the sequence is not a Boost PP seq the 
           macro forces a compiler error by outputting invalid C++.
          
           For all other compilers a compiler error is forced 
           without producing output if the sequence is not a 
           Boost PP seq.