[Boost-users] [Xpressive] Nested patterns and sub-matches' semantic values

30 May 2013

      Hi,
  For one part of a large project, I need to parse math and turn the
"mathematical objects" into a C++ abstraction of them.  Is it possible that
a nested pattern hold semantic values within itself and can be queried for
that value somehow?  As if a match were a function of its sub-patterns'
matches, if that makes sense...

Code might speak better than my english:

  class math_number {...};
  class math_addition {...};
  class math_arglist {...};
  class math_funcdef {...};

  sregex integer = (s1= +_d)
     [ return math_number( as<int>(s1) ) ];

  sregex addition = (s1= integer) >> '+' >> (s2= integer)
     [ return math_addition( as(s1), as(s2) ) ];

  sregex arglist = (s1= identifier) >> *( ',' >> (s2= arglist))
    [ std::vector ids( as(s2).begin(),
as(s2).end() );
       ids.push_back(as(s1));
       return ids; ]

  sregex funcdef = ((s1= identifier) >> '(' >> (s2= arglist) >> ")=" >>
(s3= addition))
     [ return math_funcdef( as(s1), as(s2),
as(s3) ) ];

  I just want to avoid the funcdef above to be responsible for the
construction of the various math_* objects the funcdef will hold (some of
which will be complex to construct).  And if I really must store the
objects in an external stack, how should the parent-objects find their
child-objects?

Thanks,
  Simon