Thematic, change excerpt length on Category/Archive

gistfile1.php

<?php // ignore this, it is just for the pretty code highlighting

// references
// http://codex.wordpress.org/Function_Reference/the_excerpt
// http://codex.wordpress.org/Conditional_Tags
// http://thematictheme.com/forums/topic/number-of-words-on-an-archive-page/


function childtheme_excerpt_length( $length ) {
    if ( is_category() || is_archive() ) {
        return 20;
    }
}
add_filter( 'excerpt_length', 'childtheme_excerpt_length', 999 );