Lua has a register-based VM. You're probably thinking of Lua's C API, which is stack-based. EDIT: Also, I just remembered that Lua started as a stack-based VM

Lua has a register-based VM. You're probably thinking of Lua's C API, which is stack-based. EDIT: Also, I just remembered that Lua started as a stack-based VM, but moved to register-based at around version 5. So you could be thinking of the old Lua, too.