老师我这样写是对的嘛 运行没有结果

<?php
header('content-type:text/html;charset=utf-8');
$arr=define('Throwable',[
   'Exception'=>['ClassNotFoundException'],
   'Dataformat'=>['DataFormatException'],
   'Runtime'=>['RuntimeException'],
]);
$arr2=define('Throwable',[
     'Error'=>['LinkageError'],
     'Linkage'=>['ThreadDeathError']

]);
print_r($arr);
print_r($arr2);