Executable XML users challenge

provide any LISP macro with clear explanation of its structure and function
that is :
1.concise (max 10 lines)
2.does not have a C equivalent(at least not anything above 100 lines)
3.does not use any libraries or imported complex functions which are not in C
If you provide an exact explanation/commentary on what it does i'll try to make a C solution which
is equivalent to LISP one. If i fail to do so, LISP wins, if i provide a solution you can make another macro.
If all examples in the thread are provide with C equivalents, LISP loses.

>>156
how you need a whole lexer/parser to do them properly in C
First of all, you'll have to get PhD in compiler theory, becase parsing C/C++ is a hell - even seasoned pros spend years to force something done. Ask Stroustrup, how easy it's to come with new C++0x standard.