M>Что-то я не понимаю, как у них система отображения комментов рабоатет. ПРо DSL'и против библиотек не увидел

Yes, you can use macros to enable extremely high level of code reuse, effectively 100% (if theres any kind of pattern in your code, you can write a macro to encapsulate that). But it also means that you're effectively defining your own DSL, and then writing your program in that — and when someone else needs to understand and maintain your code, they'll have to figure out that DSL first.

This isn't really fundamentally different from plain function/class libraries (they are also DSLs), but the expressivity of macros is so much higher than plain function calls (even with Smalltalk/Ruby style blocks and other such facilities) — and, consequently, so is their complexity.