I've implemented a handful of simple dynamic languages years ago, and something I was interested in trying, but never did, was taking advantage of the MMU to replace guard clauses.

For example, mapping a few pages for vtables/method dictionaries read only. When something like `def` or `define_method` comes along, catch the segfault (which in this case would actually mean "segmentation fault" instead of "I fucked up") and rewrite all JIT blocks or method caches that depend on that method table. Once everything has settled, generally after startup and the vtables tend to stay more stable, the overhead seems like it'd be negligible.