unexpected T_FUNCTION

Hi,

I haved this custom function for order my category pages by Name:

//-------Ordenar Categorías
function cat_sort_alpha( $query ) {
    if ( is_admin() || ! $query->is_main_query() )
        return; 

    if ( is_category() ) {
        $query->query_vars['showposts'] = 300;

        remove_action( 'pre_get_posts', __FUNCTION__ );
// error on this line*****
add_filter( 'posts_orderby', function() { return ' post_title ASC'; } ); 

    }
} 

add_action( 'pre_get_posts', 'cat_sort_alpha' );

After today i have this error:

PHP Parse error: syntax error, unexpected T_FUNCTION in …

The line indicated is:

add_filter( 'posts_orderby', function() { return ' post_title ASC'; } );

My site works if i comment (//) this line, but if i uncomment, the site shows a blank page.

I need this function for order my category pages.

It’s a bug? Why this worked and now is not working?

Thanks.

https://www.cruzgloriosa.org