let rec update_offset phi current offs =
match offs with
| [] -> phi current
| off::m ->
let v = Lookup.access_poffset current off in
let r = update_offset phi v m in
begin
match off with
| Lookup.Ofield f ->
F.wrap (F.upd_field (F.unwrap current) f r)
| Lookup.Oindex (i,_obj) ->
F.wrap (F.upd_index (F.unwrap current) i r)
end