Conditionally display text using ‘php if’

I currently use this piece of code to display the title, excerpt and number of comments from a post:

<?php while ($my_query->have_posts()) : $my_query->the_post(); ?>
<li><a href="<?php the_permalink() ?>"><?php the_title(); ?></a>
<?php
if( $post->post_excerpt ) {
    the_excerpt(); comments_number('(0)', '(1)', '(%)');
} else {
}
?>
</li>
<?php endwhile; ?>

This produces the following for articles that have excerpts:

Article title
Article excerpt (# comments)

And this if they don’t:

Article title

I would like to edit the code so it produces the following for articles that have excerpts:

Article title – Article excerpt (# comments)

And this if they don’t:

Article title

Presumably in order to do this I have to incorporate the text string ” – ” at some point in the if( $post->post_excerpt ) part of the code. But I don’t know how and all my efforts to do it have produced PHP errors.

I’m sure someone with a basic knowledge of PHP could solve this in a second. Any takers?

Thanks in advance…