Function tryfuncTM

ThirdParty/lua/lua/ldo.c:294–304

** Check whether __call metafield of 'func' is a function. If so, put ** it in stack below original 'func' so that 'luaD_precall' can call ** it. Raise an error if __call metafield is not a function. */

** it. Raise an error if __call metafield is not a function.
*/
static void tryfuncTM (lua_State *L, StkId func) {
  const TValue *tm = luaT_gettmbyobj(L, func, TM_CALL);
  StkId p;
  if (!ttisfunction(tm))
    luaG_typeerror(L, func, "call");
  /* Open a hole inside the stack at 'func' */
  for (p = L->top; p > func; p--)
    setobjs2s(L, p, p-1);
  L->top++;  /* slot ensured by caller */
  setobj2s(L, func, tm);  /* tag method is the new function to be called */
}