{Program Samp
  {Function facto VAL
    {if {< VAL 0 }
    then {= retVal -1}
    else {= retVal 1}
      {while {> VAL 0} do
        {= retVal {* retVal VAL}}
        {= VAL {- VAL 1}}
      }
    }
   return retVal
  }

  {print {facto 999}}
}