This kind of sounds similar to what a JIT compiler does, except that a JIT will silently fall back to slower code if you do those forbidden dynamic things. I th

This kind of sounds similar to what a JIT compiler does, except that a JIT will silently fall back to slower code if you do those forbidden dynamic things. I think the most appealing thing about what you're suggesting here is less about the peak performance and more about having better guarantees about startup cost and that performance won't be degraded (prefer failing loudly to chugging along unoptimized). These two areas often aren't the strongest point in JIT-ed systems...