math.rad (x) Converts the angle x from degrees to radians.

lua_tocfunction[-0, +0, –] lua_CFunction lua_tocfunction (lua_State *L, int index); Converts a value at the given index to a C function. That value must be a C function; otherwise, returns NULL.

luaL_checkstring[-0, +0, v] const char *luaL_checkstring (lua_State *L, int arg); Checks whether the function argument arg is a string and returns this string. This function uses lua_tolstring to get its result, so all conversions and caveats of that function apply here.

coroutine.running () Returns the running coroutine plus a boolean, true when the running coroutine is the main one.

luaL_checktype[-0, +0, v] void luaL_checktype (lua_State *L, int arg, int t); Checks whether the function argument arg has type t. See lua_type for the encoding of types for t.

lua_isyieldable[-0, +0, –] int lua_isyieldable (lua_State *L); Returns 1 if the given coroutine can yield, and 0 otherwise.

luaL_setmetatable[-0, +0, –] void luaL_setmetatable (lua_State *L, const char *tname); Sets the metatable of the object at the top of the stack as the metatable associated with name tname in the registry (see luaL_newmetatable).

lua_pcallk[-(nargs + 1), +(nresults|1), –] int lua_pcallk (lua_State *L, int nargs, int nresults, int msgh, lua_KContext ctx, lua_KFunction k); This function behaves exactly like lua_pcall, but allows the called function to yield (see §4.7).

lua_setupvalue[-(0|1), +0, –] const char *lua_setupvalue (lua_State *L, int funcindex, int n); Sets the value of a closure's upvalue. It assigns the value at the top of the stack to the upvalue and returns its name. It also pops the value from the stack. Returns NULL (and pops nothing) when the index n is greater than the number of upvalues. Parameters funcindex and n are as in function lua_getupvalue.

io.close ([file]) Equivalent to file:close(). Without a file, closes the default output file.