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<math_number>(s1), as<math_number>(s2) ) ];

  sregex arglist = (s1= identifier) >> *( ',' >> (s2= arglist))

    [ std::vector<math_id> ids( as<math_arglist>(s2).begin(), as<math_arglist>(s2).end() );

       ids.push_back(as<math_id>(s1));

       return ids; ]

  sregex funcdef = ((s1= identifier) >> '(' >> (s2= arglist) >> ")=" >> (s3= addition))

     [ return math_funcdef( as<math_id>(s1), as<math_arglist>(s2), as<math_addition>(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?