PUC Lua is slow; LuaJIT is fast but stuck at Lua 5.1 (13 years ago). yk meta-traces C interpreters to auto-derive a JIT compiler -- ~400 LoC added to PUC Lua gets ~2x typical speedup, up to ~4x on some benchmarks. yklua tracks modern Lua; LuaJIT can't. MicroPython next.