{"ast_node_type":"variable","tokens":[{"end":69,"kind":"keyword","start":0,"text":"let"}]}
            let tokens = TokenStream::new(vec![params, arrow, body]);
            let arrow = TokenTree::token_alone(token::FatArrow, pspan.between(bspan)); // `=>`
            let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());