package MyModule;
    use Assertions 'die';

    sub format_cols {
        my ($data, $columns, $width) = @_;
        ASSERT(defined ($columns) && $columns > 0, "columns is positive");
        ASSERT(defined ($width) && $width > 0);
        my $col_width = $width / $columns;

        for (1 .. $columns) {
            # ...
        }
    }