Interesting, thanks for the info. So as it seems the fact that no type checking/conversion is necessary as in dynamic languages has a positive influence on performance; but I would expect significantly less than factor two. The special AST therefore means that the interpreter is closer to a bytecode than an AST interpreter and doesn't suffer from the drawbacks of an AST interpreter, but then assumingly is not repsonsible for the measured speed-up (but instead avoiding a speed-down). The mentioned optimizations must then be responsible for the speedup, but actually also LuaJIT has many optimizations.