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.

>>207
The point is I don't see C programmers suddenly stopping, and writing LISP interpreters to maximize their productivity.
I could theoretically add a LISP-macro preprocessor which would transform my C code, but i would not be able to debug such macros
they would be like C code packed into lovecraftian structures you would need to mentally compile to understand their function.
It it a additional work which i'm not going to subject myself to, and i'll just simply write unmacroed, simple code and reusable functions.
it would be somewhat longer than Lisp, but i could understand it easily and it could be fixed, optimized and debugging without
any problem: its instantly self-evident, maximum i would lookup a macro from void.h(an C preprocessor can be much easier to understand instantly, since it just replaces text with text)