Function if

extlibs/lua/src/ltm.c:205–213

    return !l_isfalse(s2v(L->top));
#if defined(LUA_COMPAT_LT_LE)
  else if (event == TM_LE) {
      /* try '!(p2 < p1)' for '(p1 <= p2)' */
      L->ci->callstatus |= CIST_LEQ;  /* mark it is doing 'lt' for 'le' */
      if (callbinTM(L, p2, p1, L->top, TM_LT)) {
        L->ci->callstatus ^= CIST_LEQ;  /* clear mark */
        return l_isfalse(s2v(L->top));
      }
      /* else error will remove this 'ci'; no need to clear mark */
  }
#endif
  luaG_ordererror(L, p1, p2);  /* no metamethod found */
  return 0;  /* to avoid warnings */