有没有办法在PHP中输出函数的定义？

if (function_exists('function_name')) {
    echo 'Function name: ' . function_get_name('function_name');
} else {
    echo 'Function name not defined';
}

if (function_exists('function_name')) {
    $function_definition = function_get_definition('function_name');
    echo 'Function definition: ' . $function_definition;
} else {
    echo 'Function name not defined';
}