-callback fold(t(K, V), fun((K, V, Acc) -> Acc), Acc) ->
Acc.
--callback iter(t(K, V), fun((K, V) -> ok)) ->
- ok.
+-callback iter(t(K, V), fun((K, V) -> any())) ->
+ {}.
%% TODO: Decide if validation is to be done. If yes - wrap in hope_result:t/1
-callback of_kv_list([{K, V}]) ->
-callback to_kv_list(t(K, V)) ->
[{K, V}].
+
+-callback has_key(t(K, _), K) ->
+ boolean().