/**
  * @param  Snapshot $snapshot
  * @return string
  */
 public function constants(Snapshot $snapshot)
 {
     $result = '';
     foreach ($snapshot->constants() as $name => $value) {
         $result .= sprintf('if (!defined(\'%s\')) define(\'%s\', %s);' . "\n", $name, $name, $this->exportVariable($value));
     }
     return $result;
 }