static void mainfunc (LexState *ls, FuncState *fs) {
  BlockCnt bl;
  Upvaldesc *env;
  open_func(ls, fs, &bl);
  setvararg(fs, 0);  /* main function is always declared vararg */
  env = allocupvalue(fs);  /* ...set environment upvalue */
  env->instack = 1;
  env->idx = 0;
  env->kind = VDKREG;
  env->name = ls->envn;
  luaC_objbarrier(ls->L, fs->f, env->name);
  luaX_next(ls);  /* read first token */
  statlist(ls);  /* parse main body */
  check(ls, TK_EOS);
  close_func(ls);
}