oops.rs

let mut f = None;
match *e {
    expr_call(f, ref args, _) => match f.node {
        expr_path(path) => match dm.find(&f.id) {
            Some(&v) => match v {
                ast::def_variant(*) |ast::def_struct(*) => {
                    f = Some(expr_struct(
                        fld.fold_path(&path),
                        args.map(|x| fold_unnamed_field(*x)),
                        None
                    ))
                },
                _ => {}
            },
            _ => {}
        },
        _ => {}
    },
    _ => {}
}

match f {
    None => (fold::noop_fold_expr(e, fld), s),
    Some(f) => (f,s)
}