Wrodpress function

How do i convert this code into wordpress function.

<?php
add_filter('wp_get_attachment_link', 'add_gallery_id_rel');
function add_gallery_id_rel($link) {
	global $post;
	return str_replace('<a href', '<a rel="prettyPhoto'.'" href', $link);
}
if ( $post->post_type == 'game' && $post->post_status == 'publish' ) {
		$attachments = get_posts( array(
			'post_type' => 'attachment',
			'posts_per_page' => -1,
			'post_parent' => $post->ID,
			'exclude'     => get_post_thumbnail_id()
		) );

		if ( $attachments ) {
			foreach ( $attachments as $attachment ) {
				$class = "post-attachment mime-" . sanitize_title( $attachment->post_mime_type );
				$thumbimg = wp_get_attachment_link( $attachment->ID, 'thumb', false);
				echo '<li class="' . $class . ' game-thumbnail">' . $thumbimg . '</li>';
			}

		}
	}
?>