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.

>>209

Yes, debuggin macros is a pain. When I use macros, I always write them first as a regular function that operates on a list of symbols, and then I test the function on various inputs for syntax, and I make sure that its output is what is intended. Then I have the macro use the function.

One other issue is that introducing new syntax to a language requires adding new compile errors for the user. If the user gets errors for code ey didn't write, it is very confusing for ey and they'll have to examine your macro to deduce what went wrong, which is time consuming and frustrating.