After looking at the source, this appears to be a great beginners resource of how to build on top of C. The source is very concise and straightforward. I'm curious to see what will come from this.
Libcello has its share of latent macro bugs, but it doesn't seem particularly bad. However, I can hardly think of anything worse than debugging piles of half-broken higher-order C macros written by beginners.
Gonna read some more when I have time, I could learn something from this.