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.

>>203
Well if you're dead-set on replicating some braindead LISP byte by byte, you would have to write shim layers to interpret it, and obviously
not writing your own compiler/interpreter:this will too much hassle and you would need to write tons of LISP(...)
freely available compiler/intepreter : http://ecls.sourceforge.net/
You could just use ECL and the rest of the code would use C. It would not be as fast as C, and even maybe slower than some real form of Lisp, but it serves the purpose of exact processing.