{"ast_node_type":"variable","tokens":[{"end":61,"kind":"keyword","start":0,"text":"let"}]}
                    let rhs = self.collect_expr_opt(e.rhs());
                    let lhs = self.collect_expr_opt(e.lhs());
                    self.alloc_expr(Expr::BinaryOp { lhs, rhs, op }, syntax_ptr)