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.

Your macros expands wrong half the time you know it right? for example

if(test)printints(array);
will expand like
if(test);for(i=0;i<(sizeof(array)/sizeof(array[0]));i++){printf("%d ",array[i]);};puts("");

do you really know C?