Self-modifying code produces the smallest, most powerful programs you can imagine, however it also has the worst scores for MTTR BSOTTA (mean time to repair by someone other than the author). LISP will always be a fascinating language for some, but be an anathema in commercial situations where maintenance dominates. However, if you are smart enough, you can pull it off, as Autocad was written in LISP originally, and that is one of the greatest programs ever written.