Parse error php/MySql

Bonjour,

voici mon code qui me met parse error !
bool class_exists (string $Form_Input);
if (class_exists('MyClass')) {
$myclass = new MyClass();
}
abstract class Form_Input extends Form_Field {

public function __construct($name, $form) {

parent::__construct($name, $form);
$this->attrs['type'] = 'text';
}

public function get_cleaned_value($value) {

$value = trim($value);
return parent::get_cleaned_value($value);
}

// abstract public function __toString($tab = '');
public function __toString()
{
$tab = '';
$o = $tab.'<form'.$this->attrs.'>'."\n";

if (empty($this->fieldsets)) {

$o .= $this->_html_fields($tab."\t", array_diff_key($this->fields, $this->hidden_fields, $this->submit_fields));
if (!empty($this->hidden_fields)) { $o .= $this->_html_hidden_fields($tab."\t", $this->hidden_fields); }
$o .= $this->_html_fields($tab."\t", $this->submit_fields);

} else {

$hidden_fields = $this->hidden_fields;
$submit_fields = $this->submit_fields;

foreach ($this->fieldsets as $legend => $fields) {

$o .= $this->_html_fieldset($tab, $legend, $fields);

foreach($fields as $f) {

unset($hidden_fields[$f], $submit_fields[$f]);
}
}
if (!empty($hidden_fields)) { $o .= $this->_html_hidden_fields($tab."\t", $hidden_fields); }
if (!empty($submit_fields)) { $o .= $this->_html_fields($tab."\t", $submit_fields); }
}
$o .= $tab.'</form>';
return $o;
}
}

en fait je veux vérifier si ma classe existe !

Merci de votre aide