well-known register-based VMs. PCScheme's VM was also register-based. This example is the bytecode listing of the factorial function defined above (as shown by the luac 5.1 compiler): function <factorial.lua:1,7> (9 instructions, 36 bytes at 0x8063c60) 1 param, 6 slots, 0 upvalues, 6 locals, 2 constants, 0 functions 1 [2] LOADK 1 -1 ; 1 2 [3] LOADK 2 -2 ; 2 3 [3] MOVE 3 0 4 [3] LOADK 4 -1 ; 1 5 [3] FORPREP 2 1 ; to 7 6 [4] MUL 1 1 5 7 [3] FORLOOP 2 -2 ; to 6 8 [6] RETURN 1 2 9 [7] RETURN 0 1 C API Lua is intended to be embedded into other applications, and provides a C API for this purpose. The API is divided into two parts: the Lua core and the Lua auxiliary library. The Lua API's design eliminates the need for manual reference management in C code, unlike Python's API. The API, like the language, is minimalistic. Advanced functionality is provided by the auxiliary library, which consists largely of preprocessor macros which assist with complex table operations. The Lua C API is stack based. Lua provides functions to push and pop most simple C data types (integers, floats, etc.) to and from the stack, as well as functions for manipulating tables through the stack. The Lua stack is somewhat different from a traditional stack; the stack can be indexed directly, for example. Negative indices indicate offsets from the top of the stack. For example, −1 is the top (most recently pushed value), while positive indices indicate offsets from the bottom (oldest value). Marshalling data between C and Lua functions is also done using the stack. To call a Lua function, arguments are pushed onto the stack, and then the lua_call is used to call the actual function. When writing a C function to be directly called from Lua, the arguments are read from the stack. Here is an example of calling a Lua function from C: #include <stdio.h> #include <lua.h> // Lua main library (lua_*) #include <lauxlib.h> // Lua auxiliary library (luaL_*) int main(void) { // create a Lua state lua_State *L = luaL_newstate(); // load and execute a string if (luaL_dostring(L, "function foo (x,y) return x+y end")) { lua_close(L); return -1; } // push value of global "foo" (the function defined above) // to the stack, followed by integers 5 and 3 lua_getglobal(L,