{"ast_node_type":"variable","tokens":[{"end":42,"kind":"keyword","start":0,"text":"let"}]}
        let span = lo.to(self.token.span);
        let ty = if self.eat(exp!(Comma)) { Some(self.parse_ty()?) } else { None };
        Ok(self.mk_expr(span, ExprKind::UnsafeBinderCast(kind, expr, ty)))