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.

>>136
sort(function(a,b)a-b) is not particularly enlightening. Also, i find it insulting to buddhism to assume some lisp programmer can figure our the nature of reality with eval and apply, which are merely empty forms hiding the underlying computational process to which LISPers are blind as before.