parsing - php unexpected ')' parse error

$expires = time()+604800

in the function definition.

Default value can't be the result of a function, only a simple value
QUoting from the manual:

The default value must be a constant expression, not (for example) a
variable, a class member or a function call.

Use:

public function set($name,$value,$expires = NULL) { 
    if (is_null($expires))
        $expires = time()+604800;
    echo $expires; 
    return setcookie($name, $value, $expires); 
}