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.

>>56
I would just use 2 arrays and sort them separetely, with most effective sort speciazlied for the specific type.
using a mixed type array(actually an array of pointers for each element, incredibly bloated compared to int array)
make any comparison
1.first check the type of element
2.convert to common comparator type
3.compare and return result in common type
vs
1.compare two elements