{"ast_node_type":"function","tokens":[{"end":72,"kind":"keyword","start":0,"text":"fn"}]}
    fn go(diff: &mut TreeDiff, lhs: SyntaxElement, rhs: SyntaxElement) {
    // FIXME: this is horribly inefficient. I bet there's a cool algorithm to diff trees properly.
        let (lhs, rhs) = match lhs.as_node().zip(rhs.as_node()) {