Yes, I get that (in general).

But then there are things like hygiene, performance and some tricky edge-cases.

And I couldn't find any standard (and simple) algorithm to implement macros (preferably written in something other than Scheme itself).

Still trying to wrap my head around.

"This paper describes a modified form of Kohlbecker’s algo- rithm for reliably hygienic (capture-free) macro expansion in block-structured languages, where macros are source-to- source transformations specified using a high-level pattern language."

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.464...