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.

>>204
I wasn't talking about anything specific to Lisp code in >>200 or in >>203. I was talking about how you can make up any language on the fly for describing whatever you want and write a mini-compiler that generates the code for that language (this comes with all the optimization your native Lisp compiler provides). In >>200, I showed you an example of DSL and the cost that was paid by 1)google's coders' time in implementing it (DSL compiler is 10MB of code) and 2) you who are using it (custom makefile, separate compiler, specialized API and funtionality which isn't trivial to extend and so on). The cost in Lisp for making DSLs is very low (like trivial general purpose code).

So you can see that this is easy in Lisp, but not easy in C. Sure, you can just include CL in your C code if you wanted to, but if you're using CL, why not just use CL? I find it a lot less work to write CL than it is to write C, and I wrote more C code than Lisp in the past few months.