-callback get(t(K, V), K, V) ->
V.
-callback get(t(K, V), K, V) ->
V.
-callback set(t(K, V), K, V) ->
t(K, V).
-callback set(t(K, V), K, V) ->
t(K, V).
-callback fold(t(K, V), fun((K, V, Acc) -> Acc), Acc) ->
Acc.
-callback fold(t(K, V), fun((K, V, Acc) -> Acc), Acc) ->
Acc.
--callback iter(t(K, V), fun((K, V) -> ok)) ->
+-callback iter(t(K, V), fun((K, V) -> any())) ->