{"ast_node_type":"variable","tokens":[{"end":80,"kind":"keyword","start":0,"text":"let"}]}
        let items = self.rows().flat_map(|r| self.iter(r).map(move |c| (r, c)));
        write!(fmt, "BitMatrix({}x{}) ", self.num_rows, self.num_columns)?;
        fmt.debug_set().entries(items.map(OneLinePrinter)).finish()