# Create a list of files/documents that haven't been
# compared to the rest of the documents
my @new_docs = $foo->get_new_documents();
my @old_docs = $foo->get_old_documents();

# Process
my $Compare = Text::Compare->new( memoize => 1 );
foreach my $new_doc ( @new_docs ) {
    $Compare->first( $new_docs );
    foreach my $old_doc ( @old_docs ) {
        $Compare->second( $old_doc );
        $foo->save_similarity( $new_doc, $old_doc, $Compare->similarity() );
    }
}